Develop Reference

Does this Fragment equal this Fragment

So I am updating an existing old app and trying to make it more Material and more up to date.
A key area of the old app had a 'wizard' type of interface which would be a chain of Activities where the user could add Parcelable data and move forwards and backwards through the wizard using either a UI back button or the Android back button.
I've updated to Fragments all over the app and, as Google say to not have a UI back button, I am relying on the default back button.
As the default back button doesn't register for Fragments, I am trying to implement something along the lines of the solution at Vinsol
This kind of works, but I need to identify what Fragment used the back button so that I can decide what to do. This is the handler in the main Activity:
#Override
public void onBackPressed() {
if(selectedFragment == null ) {
//this isn't a Fragment we need to handle
super.onBackPressed();
}else if(selectedFragment == myFragmentOne){
//do something here for that fragment
//before going back
}else if(selectedFragment == myFragmentTwo){
//do something here for that fragment
//before going back
}
}
The null handler works ok because I set selectedFragment to null on the Fragments I'm not interested in any special handling.
But selectedFragment is either null or a Fragment. How can I check if selectedFragment is myFragmentOne or myFragmentTwo? There are no Tags to check against.

Check in this manner using instanceOf
if ( selectedFragment instanceof CustomFragmentClass) {
//put UR code
}

Using ActionBar Up Navigation in master/detail fragments

I have an app with master/detail layout (1 activity, 1 ListView fragment and 1 detail fragment). When the user clicks an item in the ListView, a fragment transaction instantiates a detail fragment on the right-pane that includes the information corresponding to that item. When the detail fragment is shown I hide the initial action bar buttons/items and show 3 new AB items (done/delete/cancel). The user can clean the right-pane and return to the initial UI state by either pressing the back button or by pressing one of the 3 AB items.
The issue I'm experiencing is that when the user selects the app's home icon (i.e. "up navigation") the activity gets re-loaded (i.e. the animation that indicates that the activity is starting can be seen as both the action bar and the UI is been redrawn). The issue only happens when the app home icon is pressed. If the user presses the back button or a cancel/done/delete action bar button, the fragment is simply remove from the right-pane and the UI returns to initial state without any "re-loading".
The XML layout for the activity is the following (inside LinearLayout; prettify is hiding that line):
<fragment class="*.*.*.ListFragment"
android:id="#+id/titles" android:layout_weight="1"
android:layout_width="0px"
android:layout_height="match_parent" />
<FrameLayout android:id="#+id/details" android:layout_weight="2"
android:layout_width="0px"
android:layout_height="match_parent" />
The DetailsFragement has the actionBar.setDisplayHomeAsUpEnabled statement in its onCreate method:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
ActionBar actionBar = getSherlockActivity().getSupportActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
}
For both the ListView fragment and the Detail fragments the onCreateOptionsMenu() and onOptionsItemSelected() method are implemented within the fragments. Below the code for the Details fragment:
#Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.edit_menu, menu);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// some variable statements...
switch (item.getItemId()) {
case android.R.id.home:
//Toast.makeText(getSherlockActivity(), "Tapped home", Toast.LENGTH_SHORT).show();
onHomeSelectedListener.onHomeSelected();
return true;
case R.id.menu_edit_item_done:
editedTask.setTitle(editedTaskTitle);
onTaskEditedListener.onTaskEdited(editedTask, UPDATE_TASK, true);
return true;
default:
return super.onOptionsItemSelected(item);
}
}
In the host activity I implement the onHomeSelectedListner to handle the app home icon press (i.e. "up navigation":
public void onHomeSelected(){
FragmentManager manager = getSupportFragmentManager();
FragmentTransaction ft = manager.beginTransaction();
TaskFragment taskFragment = (TaskFragment)getSupportFragmentManager().findFragmentById(R.id.details);
ft.remove(taskFragment);
ft.commit();
manager.popBackStack();
}
The activity's listener in charged of handling all other action bar buttons (i.e. done/delete/cancel) is onTaskEditedListener and, aside of other code that processes some data, it has the same fragment transactions shown above.
Update(1/24)
Based on tyczj and straya feedback I placed log statements inside onCreate(), onResume(), onPause() of the activity to determine the differences between onHomeSelected and onTaskEdited listeners. I'm able to confirm that during the "up navigation" event (i.e. onHomeSelected) onPause(), onCreate() and onResume() are called. Whereas during the onTaskEdited call (i.e. back button or done/delete/cancel press) none of those events are called.
Update (1/25)
Based on a suggestion by Mark Murphy, I commented out the onHomeSelected method call in the "case android.R.id.home" statement just to see what would the Activity do. The thinking was that the app would do nothing since the are no statements. Turns out that is not the case. Even without a call to the listener method (i.e. that removes the fragment), the activity is restarted and the detail fragment is removed from the fragment container.
Update (2/28)
I temporarily workaround the fact that my main activity was getting restarted by disabling the window animations (as highlighted in my own answer). However, through further testing I uncovered a bug. Thanks to Wolfram Rittmeyer's sample code I was able to figure out the real reason(s) why my activity was restarting (in master/detail single layout) during up navigation:
1) Although I was using this "onHomeSelectedListener" to properly remove the fragment from the backstack, I still had some remnant code in the ListView fragment's onOptionsItemSelected that was creating a new intent to start the hosting activity. That's why pressing the app's home icon was re-starting the activity.
2) In my final implementation (shown in my own answer), I got rid of the onHomeSelectedListener in the activity and replace the startActivity intent (i.e. offending code) inside the ListView's onOptionsItemSelected to use the fragment removal + popBackStack code originally in the onHomeSelectedListener.

After much research and poking around, turns out that only reason why my activity was restarting during "up navigation" for master/detail configuration was because I left some code in the ListView Fragment's onOptionsItemSelected that was creating an intent to start the main activity in addition to my full fragment transaction code elsewhere. Below is the final implementation with which I got "up navigation" to work properly on both phone (multiple activities) and tablet (single activity/multi-pane) configurations. Thanks to Wolfram Rittmeyer for a couple of hints in his code (link in the comment section) that help me pinpoint my problem!
Main Activity: Hosts the fragments and performs some other app-specific operations
ListView Fragment: Handles "up navigation in table configuration
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
if(mDualPane){
FragmentManager manager = getSherlockActivity().getSupportFragmentManager();
FragmentTransaction ft = manager.beginTransaction();
DetailFragment detailFragment = (DetailFragment)manager.findFragmentById(R.id.details);
ft.remove(detailFragment);
ft.commit();
manager.popBackStack();
getSherlockActivity().getSupportActionBar().setDisplayHomeAsUpEnabled(false);
getSherlockActivity().getSupportActionBar().setHomeButtonEnabled(false);
}
return true;
// Other case statements...
default:
return super.onOptionsItemSelected(item);
}
}
Details Fragment: Handles up navigation in phone configuration
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
// Sets "up navigation" for both phone/tablet configurations
ActionBar actionBar = getSherlockActivity().getSupportActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
if(!mDualPane){
Intent parentActivityIntent = new Intent(getSherlockActivity(), MainActivity.class);
parentActivityIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(parentActivityIntent);
getSherlockActivity().finish();
}
return true;
// Other case statements...
default:
return super.onOptionsItemSelected(item);
}
}

If you look at the Navigation Design Pattern you will see that you want to return to the starting activity when the home button is hit.
So say you have 2 Activities call them A1 and A2. Clicking on something in A1 takes you to A2. If the user hits the home button you should return them to A1 clearing the stack of everything up until that activity like this
Intent intent = new Intent(this, A1.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
this is what the flag Intent.FLAG_ACTIVITY_CLEAR_TOP does
If set, and the activity being launched is already running in the current task, then instead of launching a new instance of that activity, all of the other activities on top of it will be closed and this Intent will be delivered to the (now on top) old activity as a new Intent.
For example, consider a task consisting of the activities: A, B, C, D. If D calls startActivity() with an Intent that resolves to the component of activity B, then C and D will be finished and B receive the given Intent, resulting in the stack now being: A, B.`
The currently running instance of activity B in the above example will either receive the new intent you are starting here in its onNewIntent() method, or be itself finished and restarted with the new intent. If it has declared its launch mode to be "multiple" (the default) and you have not set FLAG_ACTIVITY_SINGLE_TOP in the same intent, then it will be finished and re-created; for all other launch modes or if FLAG_ACTIVITY_SINGLE_TOP is set then this Intent will be delivered to the current instance's onNewIntent().
This launch mode can also be used to good effect in conjunction with FLAG_ACTIVITY_NEW_TASK: if used to start the root activity of a task, it will bring any currently running instance of that task to the foreground, and then clear it to its root state. This is especially useful, for example, when launching an activity from the notification manager.

don't: break and then return super.onOptionsItemSelected(item), rather just: return true;
UPDATE:
So you're saying the Activity is "restarted" based on what you see happen with Views, but can you confirm what may or may not happen to the Activity (and Fragments for that matter) by using logging in the various lifecycle methods? That way you can be sure of what the current (erroneous) behaviour is before moving forward with diagnosis.
UPDATE:
OK, good to be sure about behaviour :)
Now regarding your question "What is the correct way to implement "up navigation" for a master/detail layout (1 activity/2fragments)? ":
The typical way is that the 2 Fragments got added within a single FragmentTransaction and you simply popBackStack to remove them and go back to whatever previous state was. I think you're doubling up by manually removing a Fragment within a FragmentTransaction and then popping backstack. Try just popBackStack. Oh and just to be sure and consistent, since you're using ActionBarSherlock and support.v4 are you using a FragmentActivity (rather than an Activity) and SherlockFragment?

I think you should handle the Up button only inside the activity.
If youre in a phone, the up button will be handled by activity that acts as a wrapper of that fragment, in tablet (master/detail pattern) you dont want it anyways

How to make the back function and set the last contentView

I hawe many view's in my application and now the problem is how to go back from one view to another.
What I could do it by set back Buttons in every view but i would like to use the android back hard button.
I have tried something like this:
public boolean onKeyDown(int keyCode, KeyEvent event)
{
if(keyCode==KeyEvent.KEYCODE_BACK)
{
finish();
}
return false;
}
But the problem is that this will close my application.
Could you please guide me for a proper solution, for example to memorize the last view was set and then to come back to this view or something like this.
Here is the code with which I am changing the view (it's a method in my main activity):
public void CheckIfUserIsLogedIn ()
{
int userPresence = localDatabase.CheckUserPresence();
if (userPresence == 0)
{
setContentView(R.layout.main);
}
else
{
setContentView(R.layout.userlogedon);
}
}
Thank you.

Look!
You are doing this wrong way..
An Activity class should only have on content View. (because it is recommended way and easy to use and implement).
And if you want to go to next View, show it under another separate Activity.
when you will finish it, you will be automatically redirected to previous Activity.
(and you don't need to memorize the Previous View :) )
See here, how to work with Activity Stacks.

I am not sure to understand your problem correctly because Android do all that for you automatically. Once a view is opened when you switch to another view it is paused (on screen but has not focus) or stopped (has no focus)
http://developer.android.com/reference/android/app/Activity.html
If the current view (activity) has been launched by the previous view (activity), pressing the back button will make you "close" the current view and go back to the previous one automatically.
Now two things :
Perhaps your are simply opening all views wihtin the same activity by showing on or off components which is a bad way of doing and is not recommended by android. What you should do is 1 view = 1 activity.
You are thinking like "iPhone/iPad" where you have to implements back buttons in the "views". In android you don't need to do so. Putting the "finish" command in your code at that point seem to close the application which make me think you have programmed as explained in point 1.
Hope it helps
EDIT:
To start a new activity do it like this
startActivity(new Intent(this, MyOtherActivity.class));
you put this in your code where you want to load the new view (activity)
Now if you want to transfer some information between activities you must do something like this :
Intent myIntent; //intent declaration
int aNumber = 10; // info to send to other activity
String aString = "abcd"; // info to send to other activity
// link Intent to the other activity
myIntent = new Intent(view.getContext(), MyOtherActivity.class)
//put the extra info
myIntent.putExtra("myNumber", aNumber);
myIntent.putExtra("myString", aString);
//start the new view/activity
startActivity(myIntent);
and in the new opened activity you retrieve the infos like this (in the oncreate usually)
int aNumber;
String aString;
#Override
public void onCreate(Bundle savedInstanceState) {
aNumber= getIntent().getExtras().getInt("myNumber");
aString= getIntent().getExtras().getString("myString");
}

Actually i m not sure that understand exactly but..
take a map or a shared preference and at the back button set last View on map or Shared preference .
At the calling or at start activity fetch the data which have stored you.
this will helps you.

savedInstanceState is always null

This is my savedInstaceState code:
#Override
public void onSaveInstanceState(Bundle savedInstanceState)
{
savedInstanceState.putStringArrayList("todo_arraylist", Altodo);
Log.v("bundle", "Saved");
super.onSaveInstanceState(savedInstanceState);
}
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
if (savedInstanceState != null)
{
Altodo = savedInstanceState.getStringArrayList("todo_arraylist");
Log.v("bundle", "Restored");
}
else
{
Log.v("bundle", "null");
}
setContentView(R.layout.main);
}
The logs always show the "bundle save" tag.
But in onCreate method, SavedInstanceState is always null.

I observed the exact same symptoms (reported as issue 133394) in a project with two Activities A and B that extend ActionBarActivity. Activity A is the main activity, and I always receive null for savedInstanceState in onCreate of its list fragment when returning from a detail view activity B. After many hours, this problem exposed itself to me as a navigation issue in disguise.
The following may be relevant to my setup and come from other answers on this page:
Given this answer, I made sure that fragment and activity each have unique IDs set.
There is no override of onSaveInstanceState without super call.
Activity A is specified as acitivy B's parent in AndroidManifest.xml, using both the android:parentActivityName attribute and the corresponding meta-data tag for earlier versions of Android (see "Providing Up Navigation").
Already without any corresponding creation code such as getActionBar() .setHomeButtonEnabled(true), activity B has a functioning back button (<) in its action bar. When this button is tapped, activity A reappears but with (a) all previous instance state lost, (b) onCreate always called, and (c) savedInstanceState always null.
Interestingly, when I tap the back button provided at the bottom edge of the emulator display (an open triangle that points to the left), activity A reappears just as it was left (i.e. its instance state fully retained) without invoking onCreate. So maybe something is wrong with navigation?
After more reading, I implemented my own navigation instructions to run in response to a tap on the back-button in activity B:
#Override
public boolean onOptionsItemSelected(MenuItem item) {
if (item.getItemId() == android.R.id.home)
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
Nothing related to restoring instance state of activity A changed. NavUtils also provide a method getParentActivityIntent(Activity) and navigateUpTo(Activity, Intent) that allow us to modify the navigation intent to explicitly instruct that activity A is not started fresh (and thus without saved instance state provided) by setting the FLAG_ACTIVITY_CLEAR_TOP flag:
If set, and the activity being launched is already running in the
current task, then instead of launching a new instance of that
activity, all of the other activities on top of it will be closed and
this Intent will be delivered to the (now on top) old activity as a
new Intent.
In my hands, this solves problem of lost instance state and could look like:
public boolean onOptionsItemSelected(MenuItem item) {
if (item.getItemId()== android.R.id.home) {
Intent intent = NavUtils.getParentActivityIntent(this);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
NavUtils.navigateUpTo(this, intent);
return true;
}
return super.onOptionsItemSelected(item);
}
Note that this may not be the complete solution in other cases where a user can switch directly to activity B from within a different task (see here). Also, a possibly identical solution in behavior that does not make use of NavUtils is to simply call finish():
public boolean onOptionsItemSelected(MenuItem item) {
if (item.getItemId()== android.R.id.home) {
finish();
return true;
}
return super.onOptionsItemSelected(item);
}
Both solutions work in my hands. I am only speculating that the original issue is a slightly incorrect default implementation of the back-button, and it may be related to that implementation invoking some kind of navigateUp that misses FLAG_ACTIVITY_CLEAR_TOP.

Did you check if you have an Id set for that view ( if a view it is/has...). onSaveInstanceState() is not called otherwise.
Check this link.

The state saved in this manner is not persisted. If the whole application is killed as you are doing during debugging, the bundle will always be null in onCreate.
This IMO is yet another example of awful Android documentation. It's also why most apps in the marketplace don't implement saving state properly (at all).

in Manifest add this line for activities
android:launchMode="singleTop"
for example:
<activity
android:name=".ActivityUniversity"
android:label="#string/university"
android:launchMode="singleTop"
android:parentActivityName="com.alkhorazmiy.dtm.ActivityChart">
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.alkhorazmiy.dtm.ActivityChart" />
</activity>

How do you test it?
Imo the best way to test it is using the "Don't keep activities"-flag in Settings > Developer Options. If you don't have Developer Options in Settings, see Enabling On-device Developer Options.
Open your activity
Long-press home
Go to another application
Long-press home
Go back to your application

Shouldn't super.onSaveInstanceState(savedInstanceState); be the first line in your override?
Edit: War_Hero points out in the comments that the documentation on that topic indicates that no, it shouldn't be the first line.

Check your activity in AndroidManifest.xml and remove android:noHistory property if is true.
<activity
// ....
android:noHistory="false" />

To debug, consider implementing onRestoreInstanceState and placing a call to Log.d in this method. Then, in the emulator, hit ctrl-F11 or whatever to rotate the phone. Your call to Log.d should be hit.

Implement a method of onRestoreInstanceState
and put below code there
Altodo = savedInstanceState.getStringArrayList("todo_arraylist");

I found that when I override onSaveInstanceState() and actually save some data in the Bundle, instance state is restored. Otherwise it's not.

Ive managed same way arround. Instead of handling savedInstanceState Bundle on the onCreateView method, ive handled it on onCreate method and setting the passed value to a globar variable then acessing this variable on the onCreateView method.
Hope it helps.

https://developer.android.com/guide/topics/manifest/activity-element#lmode
From this you can see 'Similarly, if you navigate up to an activity on the current stack, the behavior is determined by the parent activity's launch mode.' Maybe you are in the 'standard' mode.

I was able to solve it with:
#Override public boolean onSupportNavigateUp()
{
onBackPressed();
return true;
}
still had parent set in the manifest. So when you press the up navigation button, now it acts like the back button.

How to handle back button in activity if I have multiple screens in an activity

I have an activity which has multiple screens depending on which buttons the user clicks.
What should I do if I need to handle back button in this activity. i.e. When I press to back button it has to go previous screen of my activity.
I am really new to android. can any body help me to solve this problem
Thanks for reading.

I guess that by multiple screens you mean you have some layouts and change them with setContentView(). You'll have to override the back button's behavior, keep a history of user navigation between various screens (if there's no forced path) and have the back button code set content to the previous screen.
Overriding the back button is easy if you're on API >= 5: see onBackPressed().
If you want also backward compatibility you'll find something here and here.
As this is usually all done automatically by Android with activities, consider having multiple activities instead of a single activity with multiple screens.

override onBackPressed() function in your activity and write the desired code in it for the intent firing.

You can do this by handling the KeyDown event and adding some condition( like taking a static variable and at each activity assign different value to the static variable ) at each actvity.
See the following code:
public boolean onKeyDown(int keyCode, KeyEvent event) {
if ((keyCode == KeyEvent.KEYCODE_BACK)) {
if(condition 1)
{
Intent i=new Intent("com.prac.A"); // A is your another activity in com.prac package
startAcitvity(i);
}
else if(condition 2)
{
Intent i=new Intent("com.prac.B");
startAcitvity(i);
}
else
{
Intent i=new Intent("com.prac.C");
startAcitvity(i);
}
}
return false;
}
Hope this will help you.