I have just started programming in Android and I couldn't get the result on clicking button that I expected. Here s the code.
.java file
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.TextView;
public class AndroidLove extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_android_love);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.android_love, menu);
return true;
}
public void onButtonClicked(View view) {
TextView textView=(TextView)findViewById(R.id.textView1);
textView.setVisibility(View.VISIBLE);
}
}
.xml file
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_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=".AndroidLove" >
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginLeft="17dp"
android:layout_marginTop="104dp"
android:text="#string/hello_world"
android:visibility="invisible" />
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_marginTop="12dp"
android:text="#string/Button"
android:onClick="onButtonClicked" />
strings.xml file
<resources>
<string name="app_name">AndroidLove</string>
<string name="action_settings">Settings</string>
<string name="hello_world">First Line\nSecond Line\nThird Line</string>
<string name="Button">Get Lyrics</string>
On clicking the button, the following text should be displayed but its not displayed:-
First Line
Second Line
Third Line
Please help
Edit: Maybe and probably your binding is wrong about onclick, try below code instead of top. Put that code into your onCreate method.
Button button= (Button) findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
TextView textView=(TextView)findViewById(R.id.textView1);
textView.setVisibility(View.VISIBLE);
}
});
You need to get the string value from the strings.xml file which can be acheived by
String st =getResources.getString(R.string.hello_world);
Then set that to textview by
textView.setText(st);
Try this code:
public class AndroidLove extends Activity {
private Button button1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_android_love);
textView=(TextView)findViewById(R.id.textView1);
button1 = (Button)findViewByid(R.id.button1);
button1.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
try {
// do your stuff here
String _data =getResources.getString(R.string.hello_world);
textView.setText(_data);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
Related
For my class I have to develop a trivia game in Android Studio and I thought
I got it all figured out but now my app crashes as soon as I run it on the emulator. Can somebody tell me what's going on? It's saying i have a nullpointerException on line 24 (The line that says mQuestionTv.setText(R.string.question_text1);
This is what it says in logcat:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual
method 'void android.widget.TextView.setText(int)' on a null object
reference
at edu.unf.n01044854.unftrivia.MainActivity.onCreate(MainActivity.java:24)
Here is my java code for the app:
package edu.unf.n01044854.unftrivia;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
private TextView mQuestionTv;
private TextView mAnswerTv;
private Button mTrueButton;
private Button mFalseButton;
private Button mNextButton;
private int mCurrentIndex = 0;
private int[] mQuestionBank = new int[] {R.string.question_text1,
R.string.question_text2,
R.string.question_text3};
private boolean[] mAnswerBank = new boolean[] {true, false, true};
#Override
protected void onCreate(Bundle savedInstanceState) {
mQuestionTv = (TextView)findViewById(R.id.question_textView);
mQuestionTv.setText(R.string.question_text1);
mAnswerTv = (TextView)findViewById(R.id.answer_textView);
mTrueButton = (Button)findViewById(R.id.true_button);
mTrueButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(mAnswerBank[mCurrentIndex])
mAnswerTv.setText(R.string.correct_text);
else
mAnswerTv.setText(R.string.incorrect_text);
}
});
mFalseButton = (Button)findViewById(R.id.false_button);
mFalseButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(!mAnswerBank[mCurrentIndex])
mAnswerTv.setText(R.string.correct_text);
else
mAnswerTv.setText(R.string.incorrect_text);
}
});
mNextButton = (Button)findViewById(R.id.next_button);
mNextButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(mCurrentIndex == 3)
mCurrentIndex = 0;
else
mCurrentIndex++;
mQuestionTv.setText(mQuestionBank[mCurrentIndex]);
}
});
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
Here is the xml code for my string resources:
<resources>
<string name="app_name">UNF Trivia</string>
<string name="true_button">True</string>
<string name="false_button">False</string>
<string name="next_button">Next</string>
<string name="answer_text">Correct/Incorret</string>
<string name="correct_text">Correct</string>
<string name="incorrect_text">Incorrect</string>
<string name="question_text1">Full-stage opera productions
are offered by student performers at UNF.</string>
<string name="question_text2">The armadillo was never
considered for the mascot adoption at UNF.</string>
<string name="question_text3">UNF offers Open Zip [Line] Nights for
students.</string>
</resources>
Main Xml layout code:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical"
tools:context=".MainActivity">
<TextView
android:id="#+id/question_textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="24dp"/>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal">
<Button
android:id="#+id/true_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/true_button"/>
<Button
android:id="#+id/false_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/false_button"/>
</LinearLayout>
<Button
android:id="#+id/next_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/next_button"/>
<TextView
android:id="#+id/answer_textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/answer_text"/>
</LinearLayout>
Move these statements:
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
before any other statement inside onCreate().
Any findViewById() method you use to initialize your views must be called after the layout is inflated otherwise the views are null.
Here is the documentation of On create from android. Note that If you override this method you must call through to the superclass implementation. which is done like this:
super.onCreate(savedInstanceState);
After this, you need to inflate your view using setContentView() method. which will set the activity content from a layout resource:
setContentView(R.layout.activity_main);
Now you will be able to retrieve the widgets in that UI (activity_main) which you need to interact with programmatically.
rivate int[] mQuestionBank = new int[] {R.string.question_text1,
R.string.question_text2, R.string.question_text3};
Resources are string. Typecast resources to integer.
This is my code guys when I touch the "saldir" button or another button my app
crashes and this is my app's image https://ibb.co/ce3ATm
This is my error (https://ibb.co/jBxb16):
Dergilik APP has stopped
package com.example.rg.myapplication;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity implements
View.OnClickListener
{
int sayac =0;
TextView tv;
**//kind of turkish words don't focus the variables**
TextView tvkarekterOzellikleri;
Button byemekye;
#Override
**//THIS IS MY MAIN_Activity.Java**
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv = (TextView)findViewById(R.id.Answer);
//I'm trying very basic app when I touch button this layout'll changed
tvkarekterOzellikleri = (TextView) findViewById(R.id.Question);
Button bsaldir = (Button) findViewById(R.id.saldir);
//comment/i have 3 buttons as you can see on link at top
Button buyu = (Button) findViewById(R.id.uyu);
Button byemekye = (Button) findViewById(R.id.yemekYe);
bsaldir.setOnClickListener(this);
buyu.setOnClickListener(this);
byemekye.setOnClickListener(this);*
//This part useless now because I didn't added this part later I'll add this part
//Character k = new Character();
//k.Movementnum = 10;
//k.Kilos = 10;
//k.FightPower = 10;
//}
#Override
//This part is PROBLEM WHEN I DELETE THIS PART MY CODE IS WORKING
public void onClick(View v){
if (v.getId()==byemekye.getId())
tv.setText("yemek yenildi");
else
tv.setText("Nar" + (sayac++));
}
}
When I delete if.(v.getId....) app is running normal.
This side is my activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.rg.myapplication.MainActivity">
<Button
android:id="#+id/saldir"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:elevation="0dp"
android:text="saldir" />
<TextView
android:id="#+id/Question"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="top|bottom|center"
android:padding="3dp"
android:text="#string/Dilektasi"
android:textAppearance="#style/TextAppearance.AppCompat.Display2"
android:layout_above="#+id/saldir"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginBottom="75dp" />
<TextView
**android:id="#+id/Answer**"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/saldir"
android:layout_centerHorizontal="true"
android:layout_marginTop="70dp"
android:text="" />
//I have 3 button for my app as you can see on image
<Button
android:id="#+id/yemekYe"
**im saying twice pls dont focus on variables**
**next time i'll make this variables english**
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="#+id/saldir"
android:layout_toLeftOf="#+id/saldir"
android:layout_toStartOf="#+id/saldir"
android:text="yemek ye" />
smth smth smth smth
<Button
android:id="#+id/uyu"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="#+id/saldir"
android:layout_toEndOf="#+id/saldir"
android:layout_toRightOf="#+id/saldir"
android:text="Uyu" />
//dont focus the variable names
</RelativeLayout>
I think your problem is this:
Define Buttons:
private Button bt;
Set id of the button on xml, than on onCrate()
bt= (Button) findViewById(R.id.button1); //button1 is the id of the button
bt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
//do actions
}
});
code:
public class YourActivity extends AppCompatActivity {
private Button btn1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_post_details);
parent_view = findViewById(android.R.id.content);
btn1= (Button) findViewById(R.id.button1); //button1 is the id of the button
bt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
//do actions
}
});
}
on xml
<Button
android:id="#+id/butto1" <!-- the id -->
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Button" />
enter image description hereHey guys I'm at the end of my Java 1 class working on my project. We are making a memory/concentration game. My issue is that when I click the easy button for the next activity the app crashes. I have tried using fragments and activities and just can't seem to get it right. I have also tried using the layout I need on my main activity just to see if I could get it to display. Even then it just crashes on startup of the app. Any help would be appreciated.
Startup Screen activity.
package com.bignerdranch.android.memory;
import android.app.Activity;
import android.content.Intent;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
public class MemoryActivity extends Activity {
private Button mEasy;
private Button mMedium;
private Button mHard;
private CheckBox mSilence;
public MediaPlayer player;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_memory);
player = new MediaPlayer();
player = MediaPlayer.create(this, R.raw.mkstartmusic);
player.setAudioStreamType(AudioManager.STREAM_MUSIC);
player.setLooping(true);
player.start();
mEasy = (Button)findViewById(R.id.easy);
mEasy.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent easy = new Intent(getApplicationContext(), EasyGame.class);
startActivity(easy);
}
});
mMedium = (Button)findViewById(R.id.medium);
mMedium.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
});
mHard = (Button)findViewById(R.id.hard);
mHard.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
});
mSilence = (CheckBox)findViewById(R.id.silence);
mSilence.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(mSilence.isChecked()) {
player.pause();
} else if(mSilence.isChecked() == false) {
player.start();
}
}
});
}
#Override
protected void onStop() {
super.onPause();
if (player != null){
player.stop();
if (isFinishing()){
player.stop();
player.release();
}
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.layout.activity_memory, menu);
return true;
}
}
Second Activity (Easy option)
package com.bignerdranch.android.memory;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.ImageButton;
public class EasyGame extends Activity {
private ImageButton buttOne;
private ImageButton buttTwo;
private ImageButton buttThree;
private ImageButton buttFour;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_easy);
buttOne = (ImageButton)findViewById(R.id.ImageButton01);
buttOne.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
}
});
buttTwo = (ImageButton)findViewById(R.id.ImageButton02);
buttTwo.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
}
});
buttThree = (ImageButton)findViewById(R.id.ImageButton03);
buttThree.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
}
});
buttFour = (ImageButton)findViewById(R.id.ImageButton04);
buttFour.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.layout.activity_easy, menu);
return true;
}
}
This is the layout for the Easy option
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ImageView
android:id="#+id/easyback"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:background="#drawable/easyback"
android:clickable="false"
android:duplicateParentState="false"
android:longClickable="false"
android:scaleType="centerCrop" />
<ImageButton
android:id="#+id/ImageButton04"
android:layout_width="80dp"
android:layout_height="80dp"
android:layout_below="#+id/ImageButton01"
android:layout_toRightOf="#+id/ImageButton01"
android:layout_toEndOf="#+id/ImageButton01"
android:maxHeight="25dp"
android:maxWidth="25dp"
android:scaleType="fitXY"
android:src="#drawable/dragonemb" />
<ImageButton
android:id="#+id/ImageButton02"
android:layout_width="80dp"
android:layout_height="80dp"
android:layout_above="#+id/ImageButton04"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_marginRight="22dp"
android:layout_marginEnd="22dp"
android:maxHeight="25dp"
android:maxWidth="25dp"
android:scaleType="fitXY"
android:src="#drawable/dragonemb" />
<ImageButton
android:id="#+id/ImageButton03"
android:layout_width="80dp"
android:layout_height="80dp"
android:layout_alignTop="#+id/ImageButton04"
android:layout_toLeftOf="#+id/ImageButton04"
android:layout_toStartOf="#+id/ImageButton04"
android:maxHeight="25dp"
android:maxWidth="25dp"
android:scaleType="fitXY"
android:src="#drawable/dragonemb" />
<ImageButton
android:id="#+id/ImageButton01"
android:layout_width="80dp"
android:layout_height="80dp"
android:layout_alignParentTop="true"
android:layout_marginTop="152dp"
android:layout_toLeftOf="#+id/ImageButton02"
android:maxHeight="25dp"
android:maxWidth="25dp"
android:scaleType="fitXY"
android:src="#drawable/dragonemb" />
</RelativeLayout>
OK It's not the full crash log you posted but at the top of it I saw roidManifest.xml?. And It's sure that you didn't defined your EasyGame Activity in your androidmanifest.xml so add this line inside application tag,
<manifest package="com....." . . . >
<application . . . >
<activity
android:name=".EasyGame"
android:label="easygame">
</activity>
. . .
</application>
</manifest>
In addition you are trying to cast your ImageButton into Button consider fixing that as well.
Add code below to AndroidManfest
<activity
android:name=".EasyGame"
/>
its simple just add this line to your AndroidManifest
<activity android:name="Activity"/>
The logcat did mentioned that you need to declare your activity within the Android Manifest which you didn't. please read the logcat carefully as it really helps to find what went wrong.
OK, so I had tried all of your guys suggestions which I had were part of the issue, the final issue turned out to that I needed to add my images to the drawable-xhdpi. Thanks for all your help.
Could anyone please help me with the below java code as I want to create a image slideshow without a click of a button. I want the view flipper to automatically switch through the different iamges without a click of a button. I want it to keep on showing all the images again and again, without a click of a button. I have deleted the button in my XML file as I dont require it.
Java File Code
public class MainActivity extends Activity {
int mFlipping = 0 ; // Initially flipping is off
Button mButton ; // Reference to button available in the layout to start and stop the flipper
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/** Click event handler for button */
OnClickListener listener = new OnClickListener() {
#Override
public void onClick(View v) {
ViewFlipper flipper = (ViewFlipper) findViewById(R.id.flipper1);
if(mFlipping==0){
/** Start Flipping */
flipper.startFlipping();
mFlipping=1;
mButton.setText(R.string.str_btn_stop);
}
else{
/** Stop Flipping */
flipper.stopFlipping();
mFlipping=0;
mButton.setText(R.string.str_btn_start);
}
}
};
/** Getting a reference to the button available in the resource */
mButton = (Button) findViewById(R.id.btn);
/** Setting click event listner for the button */
mButton.setOnClickListener(listener);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}
XML File
<ViewFlipper
android:id="#+id/flipper1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:flipInterval="3000"
android:inAnimation="#android:anim/slide_in_left"
android:outAnimation="#android:anim/slide_out_right"
android:layout_centerInParent="true"
>
<ImageView
android:src="#drawable/img1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:contentDescription="#string/str_img1"
android:layout_gravity="center_horizontal"
/>
<ImageView
android:src="#drawable/img2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:contentDescription="#string/str_img2"
android:layout_gravity="center_horizontal"
/>
<ImageView
android:src="#drawable/img3"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:contentDescription="#string/str_img3"
android:layout_gravity="center_horizontal"
/>
<ImageView
android:src="#drawable/img4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:contentDescription="#string/str_img4"
android:layout_gravity="center_horizontal"
/>
<ImageView
android:src="#drawable/img5"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:contentDescription="#string/str_img5"
android:layout_gravity="center_horizontal"
/>
</ViewFlipper>
</RelativeLayout>
For(int mflipping:0;mflipping less than total images-1 length; mflipping++)
Curly brases starts
Flipper.startflipping();
//Delay for sometime
Curly Brases End
Flipper.stopflipping();
Sodu code,write your code now
Just remove button listener and try.
public class MainActivity extends Activity {
int mFlipping = 0 ; // Initially flipping is off
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ViewFlipper flipper = (ViewFlipper) findViewById(R.id.flipper1);
if(mFlipping==0){
/** Start Flipping */
flipper.startFlipping();
mFlipping=1;
}
else{
/** Stop Flipping */
flipper.stopFlipping();
mFlipping=0;
}
}
};
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}
I'm making a program for Android using Eclipse. Here is my code for MainAcitvity.java:
package com.example.changeme;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends Activity {
Button set = (Button)findViewById(R.id.set);
TextView out = (TextView)findViewById(R.id.out);
EditText in = (EditText)findViewById(R.id.input);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
set.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
setcontent();
}
});
}
public void setcontent()
{
String con = in.getText().toString();
out.setText(con);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return false;
}
}
Layout for main activity :
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_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=".MainActivity" >
<TextView
android:id="#+id/out"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/set"
android:layout_alignParentBottom="true"
android:layout_marginBottom="37dp"
android:text="#string/Change"
android:textAppearance="?android:attr/textAppearanceLarge" />
<Button
android:id="#+id/set"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/input"
android:layout_centerHorizontal="true"
android:layout_marginTop="18dp"
android:text="#string/Set" />
<EditText
android:id="#+id/input"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="37dp"
android:ems="10"
android:inputType="textPersonName" />
It crashes when I run the program on my N4.
You need to inflate your layout before retrieve your elements, otherwise findViewById will return null and hence the line set.setOnClickListener(/**/); will throw a NullPointerException which make your app crashing.
Button set;
TextView out;
EditText in;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); //<-- the layout is inflated, i.e it's rendered
/******************************************************/
//Now you can retrieve your elements from this layout
set = (Button)findViewById(R.id.set);
out = (TextView)findViewById(R.id.out);
in = (EditText)findViewById(R.id.input);
/*****************************************************/
set.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
setcontent();
}
});
}