Develop Reference

Navigating back to previous Activity

I have two Activities A and B.
Activity A has a Tablayout with some Tabs. When I navigate from A to B I use this:
Intent intent = new Intent(A, B.class);
A.startActivity(intent);
When I now navigate back from B to A I have a question:
1) When using Android's back button, the selected tab / scrolling position from A was remembered
2) When using an Intent or NavUtils.navigateUpFromSameTask(this); then the selected tab and scroll Position is NOT remembered but set to initial value
Can someone explain me what is going on here?

1) when navigation from activity A to B, the android system does not destroy activity A, but takes it to the back stack and adds B to the foreground. thats why when you press the back button or call onBackPressed() from the java code activity B is destroyed and A is set to the foreground. here is an example from the docs : Understand Tasks and Back stack
2) when using an intent/navigateUpFromSameTask activity A is recreated and set to the foreground and B is set to the background, it's like adding another activity A to the stack so it will be A,B,A but if you press the back btn then you will be back to B and then A.
if you want to keep the scroll position and other data in activity A you call the onBackPressed in B or use the onSaveInstanceState to save the data and use it in the onCreate .
here is an example of saved instance:
#Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
savedInstanceState.putString("VariableName", variableData);
savedInstanceState.putString("VariableName", variableData);
savedInstanceState.putString("VariableName", variableData);
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.penguin_main);
if(savedInstanceState!=null){
bookData = (String) savedInstanceState.getSerializable("VariableName");
bookData = (String) savedInstanceState.getSerializable("VariableName");
bookData = (String) savedInstanceState.getSerializable("VariableName");
}
}

You can set the current scroll position and tab position in activity A's on overriding onSaveInstance(Bundle savedInstanceState) method. When return to activity you can get onRestoreInstanceState(Bundle savedInstanceState) to restore it.
Hope it helps :)

Because NavUtils.navigateUpFromSameTask() just calls startActivity() and if android:launchMode="standard" the activity will be instantiated and created again and that is why can not remember the previous selected tab. To solve this issue you can override onNavigateUp() and inside that setCurrentItem(index) the index of tab you want to be displayed.
#Override
public boolean onNavigateUp() {
myViewPager.setCurrentItem(position, true);
return true;
}
Edit
You can use another solution to solve the problem by setting android:launchMode="singleTop" on activity but this solution may not applicable in all the application.

When you start an Activity, the first page will be opened! But when the back button is pressed, it navigates between the saved state of the activityTo simulate the back button pressed, you can try this:
#Override
public void onBackPressed() {
finish(); //your choice, thought not needed as super.onBackPressed(); is called if nothing is assigned here
}
or on toolbar back button clicked click:
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
finish();
}
});

how to disable the previous activity when click on the next activity

I am having multiple activity in my program the flow of it is like MainActivity-LoginActivity-NextLoginActivity etc.,I am applying transparency theme on each activity except main activity so I want when I click any activity it should show MainActivity in background rather than previous activity.

Maybe you want result below?
You open app, app into these activity in order: MainActivity -> LoginActivity -> OtherActivity
And you want to click a button that in OtherActivity, you don't want to return the LoginActivity but MainActivity
If it is, you can do this:
button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(this, MainActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
}
});
In this line: intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
Activity will use the Launch Mode by singleTask.
If activity stack has MainActivity, it will finish other activity that on top of MainActivity, then return MainActivity.

You can try to give an id to the parent layout in each activity and handle clicks on it.
Something like:
LinearLayout LoginActivity = (LinearLayout) findViewById(R.id.login_activity);
LoginActivity.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(this, MainActivity));
//If you want to close this one
//this.finish();
}
});

How to send intent data back to previous activity when back arrow icon is pressed?

I have an Android app that displays elements in a GridView: each of these elements is clickable and starts an Activity with its details; then you can go through another activity from the second one to add more data.
My question is: when I go back from 3rd to 2nd activity, my app crashes (and I know this is because going from 3rd activity to 2nd one, the 2nd so called hasn't got the intent data that it needs).
What can I do to solve this issue?
My Gridview calling the 2nd activity
gridview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
Intent i = new Intent(getApplicationContext(), PokemonDetails.class);
i.putExtra("id", position);
startActivity(i);
}
});
My 2nd activity calling the 3rd:
pokeDetails.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(getApplicationContext(), MyPokeDetails.class);
startActivity(i);
}
});

you can just override the onBackPressed() method with the same function of your buttons.
#Override
public void onBackPressed() {
//put Intent to go back here
}

Your activity should be recreated from the last state when you go back to it. Do you check the intent you have your data in in your 2nd activity to be non null? I guess the app could crash because of that.
You could also work with the savedInstanceState.
Override onSaveInstanceState and put the id you need into the bundle. If onCreate of your second Activity gets called, look if Bundle is non null and go get your value.
Further info: https://developer.android.com/training/basics/activity-lifecycle/recreating.html

You should use startActivityForResult() instead of startActivity() For details see this answer and Official documentation

setText() doesn't work after Activity change

I have button with setText() to TextView. When I click it the text changes. Next, I change activity to another and back to main activity. Now setText() doesn't work (text isn't replaced).
My code:
public void test(View view) {
String dataS = "dupa slonia";
data.setText(dataS);
System.out.println(dataS);
}

Try using onBackPressed() in the function which executes when button is clicked for going back to MainActivity.java

When you back to an Activity, you don't pass by the OnCreate method.
You have to put your code on the OnResume() method.
Take a look to the Activity Lifecycle.

onActivityResult() does not change TextView (setText()) if rotated before startActivityForResult()

This is kinda tricky. I have a profile Fragment and an 'Edit details' Button that opens a new Activity through startActivityForResult().
In onActivityResult() I reload the TextViews with the new data after editing the info through setText(). It works fine.
But if I rotated the Profile Fragment prior to clicking the edit button, the TextViews won't display the new data after saving them. It seems like onSaveInstanceState() saves the TextView texts and won't let onActivityResult() change them...

Call setText() inside runOnUiThread...
runOnUiThread(new Runnable() {
#Override
public void run() {
display.setText("new text");
}
});