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java android crash setOnClickListener

i am new in android and i was trying to make my app works in all phones
it works in 23 API and don't work in 19 API kitkat it crashes each time i open the application
Is there a way to fix this problem ?
and could you tell me what was my problem and explain it to me,
public class MainActivity extends AppCompatActivity {
private Button ButtonStart,ButtonReset ;
private TextView Number ;
private CountDownTimer myTimer ;
private MediaPlayer TimePassesSound;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButtonStart = (Button)findViewById (R.id.button); //initialize view
Number = (TextView)findViewById (R.id.textView); //initialize view
ButtonReset = (Button)findViewById (R.id.button2);
MediaPlayer TimePassesSound;
TimePassesSound = new MediaPlayer();
TimePassesSound = MediaPlayer.create(getApplicationContext(), R.raw.time_passing);
addListerOnButton (); //call method of the view
addListerOnButton2 (); //call method of the view
}
public void addListerOnButton () {
ButtonStart.setOnClickListener (
new View.OnClickListener () {
public void onClick(View v) {
if (ButtonStart.getText ().toString () != "Stop") {
int StartTime = Integer.parseInt (Number.getText ().toString ());
myTimer = new CountDownTimer (StartTime*1000, 1000) {
public void onTick(long millisUntilFinished) {
ButtonStart.setText ("Stop");
Number.setText (""+millisUntilFinished / 1000);
}
public void onFinish() {
Number.setText("60");
ButtonStart.setText ("Start");
TimePassesSound.setLooping(false);
TimePassesSound.start();
}
}.start();
} else {
ButtonStart.setText ("Start");
myTimer.cancel ();
}
}
}
);
}
public void addListerOnButton2 () {
ButtonReset.setOnClickListener (
new View.OnClickListener () {
public void onClick(View v) {
if ("Start".equals (ButtonStart.getText ().toString())) {
Number.setText ("60");
myTimer.cancel ();
}else{
Toast.makeText (MainActivity.this,"You must stop the countdown first",Toast.LENGTH_LONG).show();
}
}
}
);
}
}
public void addListerOnButton2 () {
ButtonReset.setOnClickListener (
new View.OnClickListener () {
public void onClick(View v) {
if ("Start".equals (ButtonStart.getText ().toString())) {
Number.setText ("60");
myTimer.cancel ();
}else{
Toast.makeText (MainActivity.this,"You must stop the countdown first",Toast.LENGTH_LONG).show();
}
}
}
);
}
}
-- Error messages
Process: com.aabdelrahman730yahoo.mydesign, PID: 3627
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.aabdelrahman730yahoo.mydesign/com.aabdelrahman730yahoo.mydesign.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.aabdelrahman730yahoo.mydesign.MainActivity.addListerOnButton(MainActivity.java:51)
at com.aabdelrahman730yahoo.mydesign.MainActivity.onCreate(MainActivity.java:43)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) 
at android.app.ActivityThread.access$800(ActivityThread.java:135) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:136) 
at android.app.ActivityThread.main(ActivityThread.java:5017) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
at dalvik.system.NativeStart.main(Native Method) 
Main Activity :
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="com.aabdelrahman730yahoo.mydesign.MainActivity"
android:touchscreenBlocksFocus="false"
android:background="#34416a">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Start"
android:id="#+id/button"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Reset"
android:id="#+id/button2"
android:layout_above="#+id/button"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="60"
android:id="#+id/textView"
android:singleLine="true"
android:textSize="80dp"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"/>
That's was my full problem i hope someone could help me with

You are calling the method of the view without initializing it.
You need to initialize the view first and then call the method
ButtonStart = (Button)findViewById (R.id.button); //initialize view
Number = (TextView)findViewById (R.id.textView); //initialize view
addListerOnButton (); //call method of the view
addListerOnButton2 (); //call method of the view

Check this,
As #Rod_ mentioned and from error log, it clearly states that view is not initialized.
java.lang.NullPointerException
at
com.aabdelrahman730yahoo.mydesign.MainActivity.addListerOnButton(MainActivity.java:51)
at
com.aabdelrahman730yahoo.mydesign.MainActivity.onCreate(MainActivity.java:43)
Make sure following buttons were initialized in your java code.
ButtonStart and ButtonReset -- Buttonreset is not initialized here it seems.
Change your code like below.
under oncreate
ButtonStart = (Button)findViewById (R.id.button);
ButtonReset = (Button)findViewById (R.id.button_); --> You missed it ..
Number = (TextView)findViewById (R.id.textView);
addListerOnButton ();
addListerOnButton2 ();
Hope it seems clear..!!
UPDATE:
You may not initialized the media player.
The problem may be also due to usage of media player. Kindly check the code below.
MediaPlayer mediaPlayer;
mediaPlayer = new MediaPlayer();
mediaPlayer = MediaPlayer.create(getApplicationContext(), R.raw.time_passing);
in your case
MediaPlayer TimePassesSound;
TimePassesSound = new MediaPlayer();
TimePassesSound = MediaPlayer.create(getApplicationContext(), R.raw.time_passing);
Add the above lines befor calling the functions.

Android onClick function not working

content_main.xml
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/beer_btn"
android:id="#+id/button"
android:layout_below="#+id/color"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:onClick="onClickFindBeer"/>
JAVA FILE
public class FindBeerActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.content_main);
}
public void onClickFindBeer(View view){
TextView brands=(TextView)findViewById(R.id.brands);
Spinner color=(Spinner)findViewById(R.id.color);
String beerType=String.valueOf(color.getSelectedItem());
brands.setText(beerType);
}
Hello there. While running this code The Button action is not working..
The app crashes. I cant find any error. I got this code from Head First android development tutorial.
Somebody please find the error and help me
here is the error log
05-26 09:34:30.929 19451-19451/com.example.devan.layouttut E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.devan.layouttut, PID: 19451
java.lang.IllegalStateException: Could not find method onClickFindBeer(View) in a parent or ancestor Context for android:onClick attribute defined on view class android.support.v7.widget.AppCompatButton with id 'button'
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.resolveMethod(AppCompatViewInflater.java:325)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:284)
at android.view.View.performClick(View.java:5204)
at android.view.View$PerformClick.run(View.java:21153)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Your question is not very ideal for SO and there are a lot of tutorials here and there regarding how to work with button click in Android.
But anyway, here's how you can implement the onClick on a button.
In your FindBeerActivity remove the onClickFindBeer function.
public class FindBeerActivity extends Activity {
// Get the Button variable first
private Button myButton;
private TextView brands;
private Spinner color;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.content_main);
myButton = (Button) findViewById(R.id.my_button);
brands = (TextView) findViewById(R.id.brands);
color = (Spinner) findViewById(R.id.color);
myButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String beerType=String.valueOf(color.getSelectedItem());
brands.setText(beerType);
Toast.makeText(this,"Clicked", Toast.LENGTH_LONG).show();
}
});
}
}
From your content_main.xml remove the onClick="onClickFindBeer" too.
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/beer_btn"
android:id="#+id/my_button"
android:layout_below="#+id/color"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"/>
There are of course other ways to implement onClick of a button, but I think this is the simplest.

Android - How to access a Fragment from a FragmentActivity

I always get a NullPointerException when I try to access a fragment from inside my main activity. No matter what I do.
The issue is that I use TabsPagerAdapter and ViewPager and I don't know how to get the inflated views (the fragment's onCreate() method returns the inflated view already).
The goal is to get access to an element inside the fragment and hide or show it dynamically by a single background thread which should also do this for more fragments.
MainActivity.java
public class MainActivity extends FragmentActivity implements
ActionBar.TabListener
{
/* swipe view */
private ViewPager viewPager;
private TabsPagerAdapter mAdapter;
private android.app.ActionBar actionBar;
// tab titles
private String[] tabs = { "Basic", "Advanced", "Settings"};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/* init swipe views */
mAdapter = new TabsPagerAdapter(getSupportFragmentManager());
viewPager = (ViewPager) findViewById(R.id.pager);
viewPager.setAdapter(mAdapter);
actionBar = getActionBar();
actionBar.setHomeButtonEnabled(false);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
/* addTab returns void, how to geht my fragements and their views???*/
for (String tabName : tabs)
actionBar.addTab(actionBar.newTab().setText(tabName).setTabListener(this));
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageSelected(int position) {
actionBar.setSelectedNavigationItem(position);
}
#Override
public void onPageScrolled(int arg0, float arg1, int arg2) {}
#Override
public void onPageScrollStateChanged(int arg0) {}
});
}
public void testFunction()
{
FragmentPage1 fragmentPage1 = (FragmentPage1) getSupportFragmentManager().findFragmentById(R.layout.fragment_page1);
GridLayout gridlayout = (GridLayout) fragmentPage1.getRootView().findViewById(R.id.adBannerBasicLayout);
gridlayout.setVisibility(GridLayout.VISIBLE); /* THATS MY GOAL */
}
FragmentPage1.java
public class FragmentPage1 extends Fragment {
private View rootView;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.fragment_page1, container, false);
/* HERE IT IS WORKING FINE,
but later I want to make it visible again
from code OUTSIDE FragmentPage1 ??? */
GridLayout gridlayout = (GridLayout) rootView.findViewById(R.id.adBannerBasicLayout);
gridlayout.setVisibility(GridLayout.GONE);
return rootView;
}
/* so I tried this, but also get always NullPointerException */
public View getRootView()
{
return rootView;
}
}
fragment_page1.xml
<?xml version="1.0" encoding="utf-8"?>
<ScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:ads="http://schemas.android.com/apk/res-auto"
android:id="#+id/settings_scroll_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
>
<GridLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:ads="http://schemas.android.com/apk/res-auto"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#000000"
android:orientation="vertical"
android:rowCount="12"
android:columnCount="5"
>
<!-- Some Banner Ads I want to hide show -->
<!-- I want to access this from everywhere! -->
<GridLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:ads="http://schemas.android.com/apk/res-auto"
android:id="#+id/adBannerBasicLayout"
android:orientation="vertical"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="fill"
android:rowCount="3"
android:columnCount="1"
android:layout_row="0"
android:layout_column="0"
android:layout_columnSpan="5">
<Space
android:layout_width="0dp"
android:layout_height="5dp"
android:layout_row="0"
android:layout_column="0"
/>
<com.google.android.gms.ads.AdView
android:id="#+id/adBannerBasic"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="fill"
ads:adSize="BANNER"
ads:adUnitId="xxxxxxxxxxxxxxxxxxxxxxxxxx"
android:layout_row="1"
android:layout_column="0"
>
</com.google.android.gms.ads.AdView>
<Space
android:layout_width="0dp"
android:layout_height="5dp"
android:layout_row="2"
android:layout_column="0"
/>
</GridLayout>
<!-- more stuff... -->
</GridLayout>
</ScrollView>
Please help me out, I'm totally stuck!
THANKS!
EDIT:
The scond line in testFunction() throws the NullPointerException:
GridLayout gridlayout = (GridLayout) fragmentPage1.getRootView().findViewById(R.id.adBannerBasicLayout);
because getSupportFragmentManager() always returns null:
FragmentPage1 fragmentPage1 = (FragmentPage1) getSupportFragmentManager().findFragmentById(R.layout.fragment_page1);
Logcat Outoput
java.lang.IllegalStateException: Could not execute method of the activity
at android.view.View$1.onClick(View.java:3969)
at android.view.View.performClick(View.java:4633)
at android.view.View$PerformClick.run(View.java:19330)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:157)
at android.app.ActivityThread.main(ActivityThread.java:5356)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at android.view.View$1.onClick(View.java:3964)
            at android.view.View.performClick(View.java:4633)
            at android.view.View$PerformClick.run(View.java:19330)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:157)
            at android.app.ActivityThread.main(ActivityThread.java:5356)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
            at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
            at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at org.tzapp.smote.MainActivity.testFuntion(MainActivity.java:393)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at android.view.View$1.onClick(View.java:3964)
            at android.view.View.performClick(View.java:4633)
            at android.view.View$PerformClick.run(View.java:19330)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:157)
            at android.app.ActivityThread.main(ActivityThread.java:5356)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
            at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
            at dalvik.system.NativeStart.main(Native Method)

You are using the wrong static value from the auto generated R file!
Instead of using R.layout.fragment_page1 which references the XML resource you should use R.id.fragment_page1 which should be the id of the fragment in your R.layout.activity_main XML file at /res/layout/activity_main.xml
R.layout references XML layout files
R.id references individual XML nodes (Views, Fragments etc.)
So in short, change:
FragmentPage1 fragmentPage1 = (FragmentPage1) getSupportFragmentManager().findFragmentById(R.layout.fragment_page1);
To:
FragmentPage1 fragmentPage1 = (FragmentPage1) getSupportFragmentManager().findFragmentById(R.id.fragment_page1);
And make sure that your fragment id in /res/layout/activity_main.xml is set to R.id.fragment_page1 like so:
<fragment android:name="com.example.yourpackage.FragmentPage1"
android:id="#+id/fragment_page1"
android:layout_weight="1"
android:layout_width="0dp"
android:layout_height="match_parent" />

you use getSupportFragmentManager() to get fragment.
Please double check if your FragmentPage1 extends a android.support.v4.app.Fragment;
not a
android.Fragment;

After updating SDK and repository, there is new trouble. I cant build anymore and I dont want to compile on level 23 :(
Information:Gradle tasks [clean, :app:generateDebugSources, :app:generateDebugTestSources]
:app:clean
:app:preBuild
:app:preDebugBuild
:app:checkDebugManifest
:app:preReleaseBuild
:app:prepareComAndroidSupportAppcompatV72300Library
:app:prepareComAndroidSupportSupportV42300Library
:app:prepareComGoogleAndroidGmsPlayServicesAds750Library
:app:prepareComGoogleAndroidGmsPlayServicesAnalytics750Library
:app:prepareComGoogleAndroidGmsPlayServicesBase750Library
:app:prepareComInstabugLibraryInstabugcore161Library
:app:prepareComInstabugLibraryInstabugsupport161Library
:app:prepareDebugDependencies
:app:compileDebugAidl
:app:compileDebugRenderscript
:app:generateDebugBuildConfig
:app:generateDebugAssets UP-TO-DATE
:app:mergeDebugAssets
:app:generateDebugResValues UP-TO-DATE
:app:generateDebugResources
:app:mergeDebugResources
:app:processDebugManifest
:app:processDebugResources
C:\Users\Tom\AndroidStudioProjects\SSMote\app\build\intermediates\exploded-aar\com.android.support\appcompat-v7\23.0.0\res\values-v23\values-v23.xml
Error:(1) Error retrieving parent for item: No resource found that matches the given name 'android:TextAppearance.Material.Widget.Button.Inverse'.
Error:(1) Error retrieving parent for item: No resource found that matches the given name 'android:Widget.Material.Button.Colored'.
Error:Execution failed for task ':app:processDebugResources'.
> com.android.ide.common.internal.LoggedErrorException: Failed to run command:
C:\Users\Tom\AppData\Local\Android\sdk\build-tools\21.1.2\aapt.exe package -f --no-crunch -I C:\Users\Tom\AppData\Local\Android\sdk\platforms\android-21\android.jar -M C:\Users\Tom\AndroidStudioProjects\SSMote\app\build\intermediates\manifests\full\debug\AndroidManifest.xml -S C:\Users\Tom\AndroidStudioProjects\SSMote\app\build\intermediates\res\debug -A C:\Users\Tom\AndroidStudioProjects\SSMote\app\build\intermediates\assets\debug -m -J C:\Users\Tom\AndroidStudioProjects\SSMote\app\build\generated\source\r\debug -F C:\Users\Tom\AndroidStudioProjects\SSMote\app\build\intermediates\res\resources-debug.ap_ --debug-mode --custom-package org.tzapp.smote -0 apk --output-text-symbols C:\Users\Tom\AndroidStudioProjects\SSMote\app\build\intermediates\symbols\debug
Error Code:
1
Output:
C:\Users\Tom\AndroidStudioProjects\SSMote\app\build\intermediates\res\debug\values-v23\values.xml:5: error: Error retrieving parent for item: No resource found that matches the given name 'android:TextAppearance.Material.Widget.Button.Inverse'.
C:\Users\Tom\AndroidStudioProjects\SSMote\app\build\intermediates\res\debug\values-v23\values.xml:20: error: Error retrieving parent for item: No resource found that matches the given name 'android:Widget.Material.Button.Colored'.
Information:BUILD FAILED
Information:Total time: 40.157 secs
Information:3 errors
Information:0 warnings

Also I found another answer, which is I think most satisfying :)
I forgot to mention that there is another class. It all comes from that stupid piece of example code for Swipe Views which is avaible somewhere on developers.google.com ...
Everytime I tried to access the FragmentPages via my TabPagerAdapter class using the stupid getItem(int i) method, I created a new Fragment() :-/ Very irritating!
Class TabsPagerAdapter from bad google example
public class TabsPagerAdapter extends FragmentPagerAdapter {
public TabsPagerAdapter(FragmentManager fm, MainActivity mainActivity){
super(fm);
}
// page index, fragment selector
#Override
public Fragment getItem(int index) {
switch (index)
{
case 0: return new FragmentPage1(); // bad practice
case 1: return new FragmentPage2(); // why should one do that?
case 2: return new FragmentPage3();
}
return null;
}
#Override
public int getCount() {
return 3;
}
}
What a piece of crap ^^ And I just copied it over and then totally forgot about it's existence ;)
Moved instanciation of fragments to constructor and keeped them for later use. Works perfectly now.
Class TabsPagerAdapter after optimization
public class TabsPagerAdapter extends FragmentPagerAdapter {
// hosted fragments
private FragmentPage fragmentPageBasic;
private FragmentPage fragmentPageAdvanced;
private FragmentPage fragmentPageSettings;
//constructor
public TabsPagerAdapter(FragmentManager fm, MainActivity mainActivity){
super(fm);
fragmentPageBasic = new FragmentPage();
fragmentPageBasic.setMainActivity(mainActivity);
fragmentPageBasic.setLayoutResource(R.layout.fragment_page1);
fragmentPageBasic.setAdBannerResource(R.id.adBannerBasic);
fragmentPageBasic.setAdBannerLayoutResource(R.id.adBannerBasicLayout);
fragmentPageAdvanced = new FragmentPage();
fragmentPageAdvanced.setMainActivity(mainActivity);
fragmentPageAdvanced.setLayoutResource(R.layout.fragment_page2);
fragmentPageAdvanced.setAdBannerResource(R.id.adBannerAdvanced);
fragmentPageAdvanced.setAdBannerLayoutResource(R.id.adBannerAdvancedLayout);
fragmentPageSettings = new FragmentSettingsPage();
fragmentPageSettings.setMainActivity(mainActivity);
fragmentPageSettings.setLayoutResource(R.layout.fragment_page3);
fragmentPageSettings.setAdBannerResource(R.id.adBannerSettings);
fragmentPageSettings.setAdBannerLayoutResource(R.id.adBannerSettingsLayout);
}
// page index, fragment selector
#Override
public Fragment getItem(int index) {
switch (index)
{
case 0: return fragmentPageBasic;
case 1: return fragmentPageAdvanced;
case 2: return fragmentPageSettings;
}
return null;
}
#Override
public int getCount() {
return 3;
}
// GETTERS
public FragmentPage getFragmentPageBasic() {return fragmentPageBasic;}
public FragmentPage getFragmentPageAdvanced() {return fragmentPageAdvanced;}
public FragmentPage getFragmentPageSettings() {return fragmentPageSettings;}
}
Instead of having redundant FragmentPage1, Fragment2, FragmentPage3 classes, of course now there is only FragmentPage and FragmentSettingsPage (extends FragmentPage to override OnCreateView method), which results in a much cleaner and more understandable code.
Class FragmentPage
public class FragmentPage extends Fragment {
protected MainActivity mainActivity;
// layout resource
protected int layoutResource;
// view
protected View rootView;
//Admob
protected AdView adBanner;
protected int adBannerResource;
protected int adBannerLayoutResource;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
onCreate(inflater, container);
return rootView;
}
// manage common onCreate things
protected void onCreate(LayoutInflater inflater, ViewGroup container)
{
rootView = inflater.inflate(layoutResource, container, false);
// admob banner
adBanner = (AdView) rootView.findViewById(adBannerResource);
adBanner.setAdListener(new AdListener() {
#Override
public void onAdLoaded() {
}
#Override
public void onAdOpened() {
}
#Override
public void onAdClosed() {
newAdBannerRequest();
}
#Override
public void onAdFailedToLoad(int errorCode) {
newAdBannerRequest();
}
#Override
public void onAdLeftApplication() {
}
});
if(mainActivity.showAdBanners())
{
newAdBannerRequest();
showAdBanner();
}
else
hideAdBanner();
}
// ADMOB
public void newAdBannerRequest()
{
AdRequest request = new AdRequest.Builder()
.addTestDevice(AdRequest.DEVICE_ID_EMULATOR) // All emulators
.addTestDevice("XXXXXXXXXXXXXXXXXXXXXXXXXX") // My Galaxy Nexus test phone
.build();
adBanner.loadAd(request);
}
public void showAdBanner()
{
GridLayout adBannerLayout = (GridLayout) rootView.findViewById(adBannerLayoutResource);
if(adBannerLayout.getVisibility() == GridLayout.GONE)
adBannerLayout.setVisibility(GridLayout.VISIBLE);
}
public void hideAdBanner()
{
GridLayout adBannerLayout = (GridLayout) rootView.findViewById(adBannerLayoutResource);
if(adBannerLayout.getVisibility() == GridLayout.VISIBLE)
adBannerLayout.setVisibility(GridLayout.GONE);
}
// GETTERS
public AdView getAdBanner() { return adBanner;}
public View getRootView() { return rootView;}
// SETTERS
public void setMainActivity(MainActivity mainActivity) {this.mainActivity = mainActivity;}
public void setLayoutResource(int layoutResource){this.layoutResource = layoutResource;}
public void setAdBannerResource(int adBannerResource){this.adBannerResource = adBannerResource;}
public void setAdBannerLayoutResource(int adBannerLayoutResource){this.adBannerLayoutResource = adBannerLayoutResource;}
}
Class FragmentSettingsPage
public class FragmentSettingsPage extends FragmentPage {
// Preferences
public static final String PREFS_NAME = "Preferences";
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreate(inflater, container);
SharedPreferences preferences = mainActivity.getSharedPreferences(PREFS_NAME, 0);
// do some other top secret stuff here ;)
return rootView;
}
}
Any ideas how to improve this further ?

Use import android.support.v4.app.Fragment instead import android.app.Fragment
Please add this in your gradle dependencies
compile 'com.android.support:support-v4:22.1.1'
Edit : please use findFragmentById(R.id.fragment_page1) instead R.layout
FragmentPage1 fragmentPage1 = (FragmentPage1) getSupportFragmentManager().findFragmentById(R.id.fragment_page1);

Could not find a method in the activity class android.view.ContextThemeWrapper for onClick handler

I have this problem. I am using two dialog well, one dialog on a dialog, but the second dialog crash when try to search the method. Somebody can help me?
XML: login-email
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/forgot_password_email"
android:id="#+id/login_email_tvForgetPassword"
android:layout_marginTop="18dp"
android:layout_gravity="center_horizontal"
android:onClick="openForgetPasswordSend"/>
MainActivity.java
public void openForgetPasswordSend(View view){
FragmentManager fragmentManager = getFragmentManager();
loginforgetpasswordDialogFragment.show(fragmentManager,"Forget Pass");
}
LoginForgetPassword.java
public class LoginForgetPassword extends DialogFragment{
#Override
public Dialog onCreateDialog (Bundle savedInstanceState){
// 1. Instantiate an AlertDialog.Builder with its constructor
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
//Get the Layout inflater
//LayoutInflater inflater = getActivity().getLayoutInflater();
LayoutInflater factory = LayoutInflater.from(getActivity());
//Create Dialog
Dialog dialog = new Dialog(getActivity());
//Diable title
dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
// Inflate and set the layout for the dialog
// Pass null as the parent view because its going in the dialog layout
// builder.setView(inflater.inflate(R.layout.login_register, null));
dialog.setContentView(R.layout.login_forgetpassword);
// Transparency
dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
// 3. Get the AlertDialog from create()
//return builder.create();
return dialog;
}
Error:
java.lang.IllegalStateException: Could not find a method openForgetPasswordSend(View) in the activity class android.view.ContextThemeWrapper for onClick handler on view class android.widget.TextView with id 'login_email_tvForgetPassword'
at android.view.View$1.onClick(View.java:4209)
at android.view.View.performClick(View.java:5156)
at android.view.View$PerformClick.run(View.java:20755)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5832)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
Caused by: java.lang.NoSuchMethodException: openForgetPasswordSend [class android.view.View]
at java.lang.Class.getMethod(Class.java:665)
at android.view.View$1.onClick(View.java:4202)
            at android.view.View.performClick(View.java:5156)
            at android.view.View$PerformClick.run(View.java:20755)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:145)
            at android.app.ActivityThread.main(ActivityThread.java:5832)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
I appreciated your help!

I am no expert but, don't set android:onClick="openForgetPasswordSend" It's bad practise to set click events in XML layouts.
Set all click listeners in java. Use your XML, just to setup the views.
The reason for your crash might be that, method you specify in xml has no parameters, but in the class, the method has a parameter of type View.
public void openForgetPasswordSend(View view){...}
Now, I would suggest you try the code below, this should fix your problem :
Remove
android:onClick="openForgetPasswordSend" from the <TextView>
I don't see where you use the layout'login-email.xml'. In that fragment(I assume it's in a fragment), add these lines in :
public class MyFragment extends Fragment {
private TextView myTextView;
#Override
protected void onCreate(Bundle savedInstanceState) {
mytextView = (TextView)findViewById(R.id.login_email_tvForgetPassword);
myTextView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
openForgetPasswordSend(view);
}
});
}

android java onClick Could not execute method of the activity

This is my first time working with the recyclerview and I am getting some errors about android:onClick="addItem" here is what I get when I try to add a line of text to my recyclerview. I usually use my phone to test my apps.
java.lang.IllegalStateException: Could not execute method of the activity
at android.view.View$1.onClick(View.java:4012)
at android.view.View.performClick(View.java:4761)
at android.view.View$PerformClick.run(View.java:19767)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5312)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.view.View$1.onClick(View.java:4007)
            at android.view.View.performClick(View.java:4761)
            at android.view.View$PerformClick.run(View.java:19767)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5312)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
at com.sapps.app.testapp2.MainActivity.addItem(MainActivity.java:53)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at android.view.View$1.onClick(View.java:4007)
            at android.view.View.performClick(View.java:4761)
            at android.view.View$PerformClick.run(View.java:19767)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5312)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
Here is my code where I think is the error, but I don't know exactly:
public class MainActivity extends ActionBarActivity {
private EditText mText;
private RecyclerView.LayoutManager mLayoutManager;
private RecyclerView recyclerView;
private Button btn;
private CustomRecyclerAdapter mAdapter;
private List<Data> mData = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Initializing views.
mText = (EditText) findViewById(R.id.textEt);
recyclerView = (RecyclerView) findViewById(R.id.recycler);
// If the size of views will not change as the data changes.
recyclerView.setHasFixedSize(true);
// Setting the LayoutManager.
mLayoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(mLayoutManager);
// Setting the adapter.
CustomRecyclerAdapter mAdapter = new CustomRecyclerAdapter();
recyclerView.setAdapter(mAdapter);
}
// Called when add button is clicked.
public void addItem(View v) {
if(mText!=null) {
Data dataToAdd = new Data(mText.getText().toString()); mData.add(dataToAdd);
}
}
}
And here is my recyclerview adapter to know for sure:
public class CustomRecyclerAdapter extends RecyclerView.Adapter<RecyclerViewHolder> {
CustomRecyclerAdapter mAdapter;
private List<Data> mData = Collections.emptyList();
public CustomRecyclerAdapter() {
// Pass context or other static stuff that will be needed.
}
public void updateList(List<Data> data) {
mData = data;
notifyDataSetChanged();
}
#Override
public int getItemCount() {
return mData.size();
}
#Override
public RecyclerViewHolder onCreateViewHolder(ViewGroup viewGroup, int position) {
LayoutInflater inflater = LayoutInflater.from(viewGroup.getContext());
View itemView = inflater.inflate(R.layout.list_item, viewGroup, false);
return new RecyclerViewHolder(itemView);
}
#Override
public void onBindViewHolder(RecyclerViewHolder viewHolder, int position) {
viewHolder.title.setText(mData.get(position).text);
}
public void addItemInRec(int position, Data data) {
mData.add(data);
notifyItemInserted(position);
}
public void removeItem(int position) {
mData.remove(position);
notifyItemRemoved(position);
}
}
My MainActivity xml file:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<EditText
android:id="#+id/textEt"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:hint="Text"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Add"
android:onClick="addItem"/>
</LinearLayout>
<android.support.v7.widget.RecyclerView
android:id="#+id/recycler"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scrollbars="vertical"/>
</LinearLayout>
Maybe it is my ViewHolder:
public class RecyclerViewHolder extends RecyclerView.ViewHolder {
public TextView title;
public RecyclerViewHolder(View itemView) {
super(itemView);
title = (TextView) itemView.findViewById(R.id.title);
}
}
Or Data.java class:
public class Data {
public String text;
public Data(String text) {
this.text = text;
}
}

The key is in your error message:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
at com.sapps.app.testapp2.MainActivity.addItem(MainActivity.java:53)
A good tip for learning from your error output is to look at each "Caused by" statement, and scan through the log until you find one of your own files referenced. Then that part of the error log will even tell you what line your code was failing on ( in this case it is line 53 on MainActivity.java).
A Null Pointer Exception in Java is when you attempt to call a method on some object 'A', but that object 'A' is currently null.
So this error message means:
"On line 53 of MainActivity.java, you tried to call a method on some object which doesn't exist yet, so I crashed."
The method that is failing is EditText mText = (EditText) findViewById(R.id.textEt);
Usually this type of failure means that you aren't finding the right ID from your layout. Double check that textEt is the correct ID for this layout element.
EDIT:
Still not sure why your views aren't getting populated, but I did notice an error with your adapter. You are redefining mAdapter, so you have 2 copies, one in local scope and one as a member to MainActivity. This will definitely mess things up.
Right here:
// Setting the adapter.
CustomRecyclerAdapter mAdapter = new CustomRecyclerAdapter();
recyclerView.setAdapter(mAdapter)
You are redefining mAdapter locally. Do this instead:
// Setting the adapter.
mAdapter = new CustomRecyclerAdapter();
recyclerView.setAdapter(mAdapter)

You are getting a null pointer on the getText() call
It means the following line:
EditText mText = (EditText) findViewById(R.id.textEt);
returns null, solution is to check and correct the layout so that textEt is on it.
Edit:
If you are sure that it's in the layout remove EditText declaration.
Declare as private EditText mText; on the class scope
setContentView(R.layout.name_of_layout_here);
mText = (EditText) findViewById(R.id.textEt);

The view in addItem(View v) is referring to the button only.
The EditText object that you want is not in the button, it is in the button's parent view.
If you try to access the object from the button view it will be null, because the button does not have it.
Instead you need to access the object from the button's parent view.
// Solution:
public void addItem(View v) {
View parentView = (View) v.getParent();
EditText mText = (EditText) parentView.findViewById(R.id.textEt);
Log.d("LOG", mText.getText().toString()));
}
I know that technically this does not solve the code in the question. But the code in the question has been changed from what produced the error so this would solve the original buggy code that actually produced the question.
I am guessing that the original buggy code looked like this:
// My guess this was the original buggy code
// MainActivity.java
public void addItem(View v) {
EditText mText = (EditText) v.findViewById(R.id.textEt);
Data dataToAdd = new Data(mText.getText().toString());
mData.add(dataToAdd);
}
// MainActivity.xml
<LinearLayout>
<EditText
android:id="#+id/textEt"
/>
<Button
android:text="Add"
android:onClick="addItem"/>
</LinearLayout>

Change public void addItemInRec to public void addItem. There is no method for onClick in mainActivity.