I have a menu and 5 activities. To avoid repeating the menu code, I have created a public class and call it in every activity:
Testclass testclass = new Testclass(Main.this);
...but unfortunately I can't use startActivity() in the class. This is my class code:
public class Testclass extends Activity {
public Testclass(Activity cc) {
Intent intent = new Intent(cc,Next.class);
startActivity(intent);
}
}
Try this and tell me if it helped you.
public class Testclass extends Activity {
public Testclass(Activity cc) {
final Context context = Testclass.this.getContext();
Intent intent = new Intent(context , Next.class);
context.startActivity(intent);
}
}
You misunderstood the concept of an Activity and its life cycle. You DON'T instantiate the Activity, the Activity has callback mechanisms (onCreate, onResume, etc.) that tell you exactly what to do. You never ever have to call new Activity().
The fact that you're doing
Testclass testclass = new Testclass(Main.this); shows that you have a misunderstanding of this concept: http://developer.android.com/training/basics/activity-lifecycle/index.html
To fix your error, read the docs and then it will be clear what is wrong with your approach.
Hint: Your Testclass already IS an Activity, because you inherit from Activity.
And next time please provide the whole error log to your problem, so it can give the whole picture of what can be wrong with your code.
Why not use this code?
startActivity(new Intent(Main.this, Next.class));
// "Main" is your current Activity
// "Next" is your next Activity to be opened.
I think, it's very simple to use without create a new public class. Please compare your codes with my code above, only one line.
I think you don't use the correct Context to start the Intent.
Instead try
{
public Testclass() {
Intent intent = new Intent(this,Next.class);
startActivity(intent);
}
}
if the this doesn't work either, try getApplicationContext() instead.
#you can used Weak Reference Objects to store Context of Activity class#
##in activity class##
public class Activity extends AppCompatActivity implements View.OnClickListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_view);
findViewById(R.id.toNext).setOnClickListener(this);
}
#Override
public void onClick(View v) {
Testclass thread = new Testclass(Activity.this,v);
new Thread(thread).start();
}
}
}
// in sub class
public class Testclass extends Activity implements Runnable {
View landingPage;
private Activity activity;
public Testclass (Activity activity, View landingPage){
WeakReference<Activity> ActivityWeakReference = new WeakReference<>(Activity);
this.landingPage = landingPage;
this.activity = activityWeakReference.get();
}
#Override
public void run() {
Intent activityIntent = new Intent(activity, Next.class);
activityIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
runOnUiThread(new Runnable() {
#Override
public void run() {
switch (landingPage.getId())
{
case R.id.Next.class:
activity.finish();
activity.startActivity(activityIntent);
break;
}
}
});
}
}
Related
I have two classes, both of which extend Activity.
MainActivity.java
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
LinearLayout activityLayout = new LinearLayout(this);
LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(
LinearLayout.LayoutParams.MATCH_PARENT,
LinearLayout.LayoutParams.MATCH_PARENT);
activityLayout.setLayoutParams(lp);
activityLayout.setOrientation(LinearLayout.VERTICAL);
activityLayout.setPadding(16, 16, 16, 16);
activityLayout.addView(new Button(this));
setContentView(activityLayout);
new Permissions() {
#Override
public void onPermissionRefused() {
Toast.makeText(getBaseContext(), "Refused", Toast.LENGTH_SHORT).show();
}
}.requestPermissions(this);
}
}
Permissions.java
public class Permissions extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
setTheme(R.style.AppTheme_Dialog); // Custom theme to make Activity like a Dialog
super.onCreate(savedInstanceState);
onPermissionRefused();
}
public void requestPermissions(Activity activity, String... permissions) {
startActivity(new Intent(activity, Permissions.class));
}
public void onPermissionRefused() {
}
}
What I want to do is start the Permissions Activity while overriding it's onPermissionRefused() method. However, neither of the two ways I've tried work.
new Permissions() {
#Override
public void onPermissionRefused() {
Toast.makeText(getBaseContext(), "Refused", Toast.LENGTH_SHORT).show();
}
}.requestPermissions(this);
Doesn't pass the override and swapping that code out with: startActivity(new Intent(this, Permissions.class)); doesn't even allow me to override the method. How can I achieve this?
Step 1. Create a subclass of Permissions
class MyPermissionsActivity extends Permissions {
#Override
public void onPermissionRefused() {
Toast.makeText(getBaseContext(), "Refused", Toast.LENGTH_SHORT).show();
}
}
Step 2. Declare that subclass in your application manifest
Step 3. Launch the activity as follows:
Intent i = new Intent(context, MyPermissionsActivity.class);
currentActivity.startActivity(i);
You can't. Activities have to be declared in the manifest, you can't declare an anonymous inner class that way (and even if you could, it wouldn't have the right constructor because of the implicit reference to parent). If you need that, make a real subclass, and pass any necessary variables via intent.
I want to modularize the usage of my class but I have problem in passing function. I want to be able to pass an OnClickListener from 1 activity to this CoachmarkActivity.
I tried 2 different method:
1. Passing an OnClickListener to Intent
2. Passing a class, FollowUpClass, implements Serializable, which has method onClick.
You can see the code below. It is not complete code, but you should be able to comprehend this.
public class CoachmarkActivity extends Activity {
public static final String RES_LAYOUT = "RES-LAYOUT";
public static final String LISTENER = "LISTENER";
public static final String FOLLOW_UP = "FOLLOW-UP";
#Override protected void onCreate(Bundle savedInstance) {
setContentView(getIntent.getIntExtra(RES_LAYOUT, R.layout.activity_default))
Button button1 = (Button) findViewById(R.id.button1);
Button button2 = (Button) findViewById(R.id.button2);
// 1ST ATTEMPT
// I want to modularize this
OnClickListener onClickPassedFromIntent = (OnClickListener) getIntent().getSerializableExtra(LISTENER);
button1.setOnClickListener(onClickPassedFromIntent);
// 2ND ATTEMPT
final FollowUpListener folllowup = (FollowUpListener) getIntent().getSerializableExtra(FOLLOW_UP);
button2.setOnClickListener(new OnClickListener() {
#Override void onClick() {
// !! Here is error, exception thrown
folllowup.onClick();
}
});
}
/**
* Public method to be used in other activity.
* Invocation wanna be:
* CoachmarkActivity.startThisActivity(getActivity(), R.layout.coachmark1, new OnClickListener() {
* #Override void onClick() {
* // Do something
* }
* });
*/
public static void startThisActivity(Context context, int resId, OnClickListener listener) {
Intent intent = new Intent(context, CoachmarkActivity.class);
intent.putExtra(RES_LAYOUT, resId);
// !! Line below is error, onClickListener is not serializable, no method can accomadate below
intent.putExtra(LISTENER, listener);
context.startActivity(intent);
}
/**
* Public method to be used in other activity.
* Invocation wanna be:
* CoachmarkActivity.startThisActivity(getActivity(), R.layout.coachmark1, new FollowUpListener() {
* #Override void onClick() {
* // Do something
* }
* });
*/
public static void startThisActivity(Context context, int resId, FollowUpListener folllowup) {
Intent intent = new Intent(context, CoachmarkActivity.class);
intent.putExtra(RES_LAYOUT, resId);
intent.putExtra(FOLLOW_UP, followup);
context.startActivity(intent);
}
}
The abstract class:
public abstract class FollowUpListener implements Serializable {
public abstract void onClick();
}
The problems are stated in the comment in source code above, with tag "!!" (Just CTRL+F "!!"). What I want to do is like passing a Delegate object (function in form of variable) in C#, but in Android Java.
Any idea? Thanks.
You are trying to add a Serializable extra to your Intent, but OnClickListener does not implement that interface. You can achieve what you want by creating a class that implements both of the interfaces you need.
private class SerializableClickListener implements View.OnClickListener, Serializable {
#Override public void onClick() {
// TODO handle click
}
}
However, just because you can doesn't mean you should. Sending a click listener to another activity is a horrible code smell, and you should really rethink how you could do this via Intents/Broadcasts.
I tried to pass the OnlclickListener and I couldn't. then I tried this solution.
I made a static click listener variable in a GlobalData class
public static View.OnClickListener btn;
Then when I call the startactivity to go to another activity I did this.
GlobalData.btn = new View.OnClickListener() {
#Override
public void onClick(View v) {
//Listern action
}
};
c.startActivity(new Intent(c, DialogActivity.class));
Then in the second activity, I can set the static listener reference which I used to assign a listener object in the first activity.
b1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(GlobalData.btn!=null){
GlobalData.btn1.onClick(v);
}
finish();
}
});
I didn't use it directly as a parameter so I can do other stuff in the second activity listener. this worked for me.
But you have to think more because you are using a static reference. this is not a 100% solution. but it's worth trying.
There are two Activities..
1. Open SecondActivity from MainActivity
2. When event comes into MainActivity, call testMethod of SecondActivity
But how to do call this testMethod?
public class MainActivity extends Activity implements someListener {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Launch SecondActivity here!!
Intent intent = new Intent();
intent.setClass(MainActivity.this, SecondActivity.class);
startActivityForResult(intent, ID_PlayerActivity);
}
//trigger by JNI, it's in the other thread, not main thread.
void onEventCome() {
//How to call testMethod() in SecondActivity?
}
}
public class SecondActivity extends Activity {
void testMethod() {
//execute something...
}
}
If you open the SecondActivity, your MainActivity becomes inactive. I don't believe it is a good idea to call some activity method from other inactive/stopped activity.
I suggest to use observer pattern. Create a global long-lived object like EventProducer and register all activities as observer. So your EventProducer can inform all Activities about new event.
Example:
public class SecondActivity extends Activity implements MyEventListener {
#Override
public void onResume(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
EventProducer.instance().register(this);
}
#Override
public void onPause(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
EventProducer.instance().unregister(this);
}
void testMethod(){
//just doit
}
#Override
void onMyEventCome() {
testMethod();
}
}
First you need an event aware listener that will capture such an event happening. Your class seems ill equipped to do so.
Since you have a valid question, here goes:
void onEventCome() {
SecondActivity secondActivity = new SecondActivity();
secondActivity.testMethod();
}
There are many ways.
For eg:
Create the method as static and use class name and call it.
public static void onEventCome() {
}
In MainActivity:
MainActivity.onEventCome();
This is one method. Another method is create an object for MainActivity.
public void onEventCome() {
}
MainActivity main;
main = new MainActivity();
main.onEventCome();
You don't have a content view for your second activity. If you don't need to see the operation happen, you could remove your
Intent intent = new Intent();
intent.setClass(MainActivity.this, SecondActivity.class);
startActivityForResult(intent, ID_PlayerActivity);
remove extends Activity in SecondActivity and add a constructor public SecondActivity(Context context) and invoke the test method from your first activity like #Dragan example:
void onEventCome() {
SecondActivity secondActivity = new SecondActivity(MainActivity.this);
secondActivity.testMethod();
}
I have an Activity class.
public class A extends Activity
{
}
Then I have a class that is not an Activity but I want it to start the Activity A.
public class B
{
public B()
{
Intent I = new Intent(null, A.class);
i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
}
}
The code is take from this question which should work: Calling startActivity() from outside of an Activity?
However, when I run it I never change from my first activity to activity A. What am I doing wrong? Should I be listening to the FLAG_ACTIVITY_NEW_TASK inside A?
Something like this should work:
public class B {
Context context;
public B(Context context) {
this.context = context;
}
public void startNewActivity(String str) {
try {
Intent i = new Intent(context, Class.forName(str));
i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(i);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
Use case of class B:
B b = new B(A.this);
b.startNewActivity("MainActivity");//the "MainActivity" is the className of the java class
Note I find this way wierd and a overkill.
I'm trying to pass something from one class to my MainActivity, but it doesn't seem to work, I don't understand why.
I have my GPS Tracker on another class (not the MainActivity) in order to reuse it.
When the location changes, I want my other class to call a method from within the MainActivity to update my UI.
I summarized my code like that :
My MAIN ACTIVITY :
public class MainActivity extends Activity implements OnClickListener {
TextView tv;
EditText et;
Button btun;
int arg0;
int stuff;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv = (TextView) findViewById(R.id.tv);
et = (EditText) findViewById(R.id.et);
btun = (Button) findViewById(R.id.btun);
btun.setOnClickListener(this);
}
private void setter(int stuff) {
tv.setText(stuff);
}
public void setText(int _stuff) {
_stuff = stuff;
setter(_stuff);
}
#Override
public void onClick(View v) {
Getter get = new Getter();
get.getInfo(Integer.parseInt(et.getText().toString()));
}
The other Class :
public class Getter {
int _getString;
MainActivity main = new MainActivity();
public void getInfo(int getString) {
_getString = getString * 8;
main.setText(_getString);
}
}
I end up having a NullPointerException in my LogCat
at :
- tv.setText(stuff);
- setter(_stuff);
- main.setText(_getString);
- get.getInfo(Integer.parseInt(et.getText().toString()));
and I don't really know why, and above all, how to fix it.
I'll appreciate any help !
(PS : My GPS tracker thingy is working fine, it's just about invoking my setter() method.
Instantiaing an Object of MainActivity doesn't automatically call onCreate method but this method is called when you start an activity using Intent; And using the same intent you can pass extra values. For example:
Intent intent = new Intent(context, MainActivity.class);
intent.putExtra("key", value);
context.startActivity(intent);
and then in your main activity onCreate method:
String value = getIntent.getStringExtra("key");
Edit:
In your case why don't you change your void getInfo(int getString) to return a String value i.e.
public class Getter {
...
...
public String getInfo(int getString) {
_getString = getString * 8;
return Integer.toString(_getString);
}
}
and then in onClick event of MainActivity bind this returned text to TextView
It's maybe because the MainActivity's onCreate()-Method hasn't been called. Therefore the tv is still null causing the NullPointerException
One problem is here. main is an Activity, but it should be the MainActivity calling this object.
public class Getter {
int _getString;
MainActivity main = new MainActivity();
public void getInfo(int getString) {
_getString = getString * 8;
main.setText(_getString);
}
}
I cannot really make out what you are trying to achieve in the Getter class, but either:
1: Pass the Activity instance to the object
public class Getter {
int _getString;
MainActivity _main = null;
public Getter(MainActivity main) {
_main = main;
}
public void getInfo(int getString) {
_getString = getString * 8;
_main.setText(_getString);
}
}
#Override
public void onClick(View v) {
Getter get = new Getter(this);
get.getInfo(Integer.parseInt(et.getText().toString()));
}
or
2: set the text in the Activity and only get the value from the Getter (My choice)
public class Getter {
int _getString;
MainActivity main = new MainActivity();
public void getInfo(int getString) {
return getString * 8;
}
}
#Override
public void onClick(View v) {
Getter get = new Getter();
int info = get.getInfo(Integer.parseInt(et.getText().toString()));
setText(Integer.toString(info));
}
Use Application Class or create a separate Class and declare a static variable in it. Use getter & setter methods to get the value. To update the Textview in mainacivity from other class pass the texview reference variable from main activity and put null check condition in other class if textview is not null then update the value.