Develop Reference

Call fragment method from activity but view is null

I am checking internet connection in my main activity.If connection is lost,I want to show reconnecting message in fragment.Example:If I run following code in main activity my app is crashing.
ConversationFragment conv1 = new ConversationFragment();
conv1.showReconnecting();
And this is the showReconnecting method in fragment:
public void showReconnecting() {
final RelativeLayout rel=(RelativeLayout)rootView.findViewById(R.id.reconnecting);
rel.setVisibility(View.VISIBLE);
}
I know why my app is crashing because rootView is setting in onCreateView and when I call this method from activity rootView is returning null.
What can I do for resolve this problem ?

Try this (Assuming reconnecting view is in fragment and your fragment is visible on screen),
public void showReconnecting() {
if (conv1 != null && conv1.getView()!=null) {
final RelativeLayout rel=(RelativeLayout)conv1.getView().findViewById(R.id.reconnecting);
rel.setVisibility(View.VISIBLE);
}
}
If conv1 is not available then please make it class variable.

According to what you want to do, a simple ProgressDialog will do the job. You can lauch it from your ChatFragment, like this:
First, declare it on your Fragment:
private ProgressDialog connectiongProgressDialog;
Then, when you want to show it, use:
connectiongProgressDialog = ProgressDialog.show(getActivity(), "My title", "Reconnecting");
When you want to dismiss it, use:
if (connectiongProgressDialog != null){
connectiongProgressDialog .dismiss();
}
It will display a simple dialog with the message you want.

Well, just looking at this and your explanation, I would think you can't call methods relating to a view (such as a fragment) without creating said fragment. An option, if the fragment is only used for showing the reconnecting, would be just to put some code in the activity and use a Toast.makeText(....).show();
which notifies the user that you are attempting to reconnect. So instead of conv1.showReconnecting(); maybe rather put, Toast.makeText(context,"Reconnecting", Toast.LONG).show(); and then do the necessary background work in an AsyncTask.
I hope this helps.

Calling an activity from a fragment - activity doesn't run

New to Android so bear with me.
I have a fragment (DirectionsFragment) that calls an Activity to get some data from Yelp (YelpActivity).
When I run the YelpActivity itself, without calling it from DirectionsFragment, it runs succesfully (displays the received information, prints out appropriate log messages, etc.).
However, when I create YelpActivity from the fragment, nothing happens - no log messages, no retrieved information.
Here's how I create the YelpActivity
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
YelpActivity ya = new YelpActivity();
}
Thanks

Activity is started by startActivtiy(intent). But you have
YelpActivity ya = new YelpActivity();
Should not create an instance of Activity class.
Use
startActivity(new Intent(getActivtiy(),YealpActivtiy.class);
Make sure you have declared the activity in manifest file

Pass reference of one Activity to another Activity

I know that I can pass some values between Activities using intent.
However, if I want to pass whole Activity to another Activity I think it is not good approach.
Is there another way to do that?
I have Settings Activity in which I am changing some Colors. So after I come back to my Main Activity I would like to apply those colors. To do this, I need access to MainActivity fields after I change Color value, so inside PreferenceActivity. In other words, I want to have access to Main activity fields from PreferenceActivity class. Any ideas?

You should be using a SharedPreference and then accessing that in your main activity. I recommend you reading up at http://developer.android.com/guide/topics/ui/settings.html because it seems like you are implementing your settings activity incorrectly. The part you might be specifically interested in is the "Read Preferences" section. However, I strongly suggest you read through the whole thing and then implement your settings the proper way.
Updated answer with the 3 different ways (that I can think of):
1) Start your preference activity using startActivityForResult(), then in your onActivityResult() access the SharedPreference and make your necessary changes. See here
2) Register a SharedPreferenceChangeListener with your MainActivity, which will be called when any changes happen to your SharedPreference. See here for a detailed discussion. Also see my initial response.
3) In your MainActivity's onResume(), access the SharedPreference and then make your changes there. I do not like this method because you will be cluttering onResume() with more logic and you will also probably have to have a variable that keeps track of the state of the variable you are interested in.
I would personally go with option 2 because the callback was created for this exact purpose.

I think you could pass the value by using method putExtra(name, value).
And after you start new activity you can get the value you pass before by using method getStringExtra(name).

Shared preferences can be used. If you want your changes to be reflected right away add listener. Refer to SharedPreferences.onSharedPreferenceChangeListener. Its an easy way to do.

If you want to lots of changes required in many activity from you change in any one.
And access last modify data from all Activity and modify also.
for example.
Constants.java
public class Constants
{
public static String name;
}
In your MainActivity you have an editText.
MainActivity.java
public class MainActivity extends Activity {
private EditText yourName;
private Button btn;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
yourName = (EditText) findViewById(R.id.yourName);
btn = (Button) findViewById(R.id.btn);
btn.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
Constants.name = yourname.getText().toString();
Intent intent = new Intent(getApplicationContext(),Activity2.class);
startActivity(intent);
}
});
}
In your Activity2 you have an TextView and that getting value which you enter in MainActivity.java without pass in Intent.
Activity2.java
public class Activity2 extends Activity {
private TextView yourName;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
yourName = (TextView) findViewById(R.id.tv_yourName);
// directly use ferom serializable class
yourname.setText(Constants.name);
}
like that you use many values from all activity and modify from all activity.

onResume() not called second time an Activity is launched

During the normal course of development, I noticed that a particular activity appears to have stopped responding the second time it is called.
i.e. menu->(intent)->activity->(back button)->menu->(intent)
There is nothing relevant in logcat.
I don't even know where to start debugging this nor what code to show so here are the onClick and onResume fragments:
if (!dictionary.getClassName().equals("")) {
this.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
Intent i;
i = new Intent(mContext, NVGlobeNavigatorVC.class);
i.putExtra("PAGE_TITLE", title);
i.putExtra("TITLE", _dictionary._title);
mContext.startActivity(i);
});
} else {
findViewById(R.id.greaterthan).setVisibility(View.GONE);
}
and in the Activity being launched:
#Override
protected void onResume() {
super.onResume();
...
Nothing unusual in manifest either:
<activity
android:name=".NVViews.NVGlobeNavigatorVC"
android:theme="#style/WindowTitleBackground"
android:label="GlobeNavigator"/>
For clarity, I put breakpoints on mContext.startActivity(i) and super.onResume(). I click the view with the onClickListener and both breakpoints are hit as expected. I then press the back button which returns me to the menu. onPause() is called as expected.
I touch the view to launch the activity again, and the breakpoint on startActivity is hit but not in onResume() in the target activity. The screen goes black and the only way I can get going again is to restart the app. If I pause the debugger, it pauses in dalvik.system.NativeStart() which implies that the activity is never relaunched.
I don't think it's relevant, but I'm using Intellij IDEA and have deleted all of the output directories, invalidated the caches and done a full rebuild.
Target API is 8. I've tested on 2.3 and 4.0.4.
Any ideas? I'm stumped.
[EDIT]
In onPause, I save some stuff to prefs. The purpose of onResume() is to get them back again:
#Override
protected void onPause() {
super.onPause();
SCPrefs.setGlobeViewViewPoint(globeView.getViewPoint());
SCPrefs.setGlobeViewZoom(globeView.getZoom());
SCPrefs.setGlobeViewScale(globeView.getScale());
}

This code:
i = new Intent(mContext, NVGlobeNavigatorVC.class);
creates a new intent. The intent is of class NVGlobeNavigatorVC.class.
If you call it once, you create a new activity, lets call it "iTheFirst". If you back out of the activity, it executes "on pause". When you run the above code again, you create another new activity of the same class, but a different acitivity. Hence it won't resume your other activity, but make a new one that we could call "iTheSecond". It looks just like iTheFirst but is unique.
If you want to resume the above, after backing out of it, you need to keep a reference to it in your menu. Then in your onClick, look to see if that activity exists, and if not, make a new one and start it, and if it does exist, just resume it.
Here is a sample activity that remembers and restarts an activity:
Intent savedCueCardActivity = null;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState, R.layout.landing);
}
public void goToNextScreen(View v) {
if (savedCueCardActivity == null) {
savedCueCardActivity = new Intent().setClass(this, CueCardActivity.class);
startActivity(savedCueCardActivity);
// lastActivity.finish();
} else {
savedCueCardActivity.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivity(savedCueCardActivity);
}
overridePendingTransition(R.anim.fade_in, R.anim.fade_out);
}

I found the problem, and it's a bit esoteric.
I have a large static data structure which is loaded in a class static initialiser. There was a bug in that initialiser causing an infinite loop the second time it was called if the data structure was still loaded.
Because that class is referenced in my Activity, the class loader is loading it before onCreate() or onResume() is called.
The loop gave the appearance that the Activity loader had hung.

App is crashing after Home is pressed. Unable to pause - Derived class did not call super.onSaveInstanceState()

When I press the Home button, the app should be paused, save all state and work fine.
Instead I get this error:
java.lang.RuntimeException: Unable to
pause activity
{be.test.tester/be.test.tester.DataScreen}:
java.lang.IllegalStateException:
Derived class did not call
super.onSaveInstanceState() at
android.app.ActivityThread.performPauseActivity(ActivityThread.java:3641)
at
android.app.ActivityThread.performPauseActivity(ActivityThread.java:3598)
at
android.app.ActivityThread.handlePauseActivity(ActivityThread.java:3574)
at
android.app.ActivityThread.access$2500(ActivityThread.java:136)
at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:2186)
at
android.os.Handler.dispatchMessage(Handler.java:99)
at
android.os.Looper.loop(Looper.java:143)
at
android.app.ActivityThread.main(ActivityThread.java:5068)
at
java.lang.reflect.Method.invokeNative(Native
Method) at
java.lang.reflect.Method.invoke(Method.java:521)
at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
at
dalvik.system.NativeStart.main(Native
Method)
Caused by:
java.lang.IllegalStateException:
Derived class did not call
super.onSaveInstanceState() at
android.view.View.dispatchSaveInstanceState(View.java:6087)
at
android.view.ViewGroup.dispatchSaveInstanceState(ViewGroup.java:1207)
at
android.view.ViewGroup.dispatchSaveInstanceState(ViewGroup.java:1207)
at
android.view.View.saveHierarchyState(View.java:6068)
at
com.android.internal.policy.impl.PhoneWindow.saveHierarchyState(PhoneWindow.java:1475)
at
android.app.Activity.onSaveInstanceState(Activity.java:1106)
at
android.app.Activity.performSaveInstanceState(Activity.java:1056)
at
android.app.Instrumentation.callActivityOnSaveInstanceState(Instrumentation.java:1289)
at
android.app.ActivityThread.performPauseActivity(ActivityThread.java:3623)
... 12 more
My activity reacts on touch:
public class DataScreen extends Activity implements OnGestureListener{
I'm getting some extra's from the intent:
totUsage = Integer.parseInt(getIntent().getStringExtra("extraTotUsage"));
limit = Integer.parseInt(getIntent().getStringExtra("extraLimit"));
Bundle bundle = getIntent().getExtras();
mylist = (ArrayList<HashMap<String, String>>) bundle.get("extraMyList");
A custom view is showing data (canvas). When you scroll on screen, data changes in custom view (set, get method) and redraws itself.
I don't really manage the onSaveInstanceState here, don't really know if I have to.
My app is onTop of the stack, because of:
i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
I don't understand the error.

You should override onSaveInstanceState and call its super method like shown below. At least it helped me with the same problem.
#Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
// your stuff or nothing
}
#Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// your stuff or nothing
}

I've just been dealing with this problem. In my app the main activity allows a second activity to be called to display info/instructions etc, it also has a surface view that draws the runtime element of the app.
The main activity has a variable to hold the surface view, if that variable hasn't been set before the info/instructions activity is called I get this error. I simply moved the surface view variable assignment into the main activity onCreate and all is well.

It is also possible that one uses a custom preference (e.g. custom dialog preference) that does not call "super.onSavedInstanceState()" which leads to the same error.