Set intent when returning to parent activity

Issue

An application about which I previously asked requires an ID for a particular activity, which is used to make a database query. When the activity starts I get this ID from an intent, thus:

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_counting);

    Bundle extras = getIntent().getExtras();
    if(extras !=null)
    {
      project_id = extras.getLong("project_id");
    }
    // ... the rest of the initialisation follows here
}

This activity (CountingActivity) in turn starts another via the user's interaction (EditProjectActivity) which has the CountingActivity as a parent so that navigation back via the home button works. In AndroidManifest.xml I have this:

    <activity
        android:name="myproject.EditProjectActivity"
        android:label="@string/title_activity_edit_project"
        android:theme="@style/Theme.AppCompat"
        android:parentActivityName="myproject.CountingActivity" >
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="CountingActivity" />
    </activity>

When a user has finished editing they could do one of three things:

1. Press a 'save' button. The data are saved, finish() is called and the CountingActivity returns.
2. Press the Android back button. The EditProjectActivity is popped off the stack without saving and the Counting Activity returns.
3. Press the application icon in the top left. Somehow, the CountingActivity is started without the project_id intent; this value ends up being set to 0 and nothing can be found in the database, with undesirable results.

Somehow, I need to make sure that the project_id is passed as an intent when navigating back to the parent activity. I tried this without luck:

@Override
public boolean onOptionsItemSelected(MenuItem item)
{
    int id = item.getItemId();
    if (id == R.id.home) // I also tried R.id.homeAsUp
    {
        Intent intent = new Intent(EditProjectActivity.this, CountingActivity.class);
        intent.putExtra("project_id",project_id);
        intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(intent);
    }
    return super.onOptionsItemSelected(item);
}

But, there's still no project_id and so a database query can't be made. So, if anyone could point me in the right direction I'd appreciate it.

Solution

When you use android.support.PARENT_ACTIVITY, the parent activity must be set as singleTop or FLAG_ACTIVITY_CLEAR_TOP. Otherwise a new instance will be created. See for example Android: Activities destroyed unexpectedly, null savedInstanceState

However, depending on the use case, a simpler alternative may be available. If EditProjectActivity is always called from CountingActivity (and never by itself) and you always want to return there, the simplest solution is to just use:

if (id == R.id.home)
{
    setResult(...); // optional, whether you want to treat this as save/cancel.
    finish();
}

Answered By - matiash