Up Button Calls OnDestroy of Parent Activity

问题

Right off the top, I want to clarify something: The button that I am struggling with is NOT the back button. I am referring to the up/home button in the ActionBar / Toolbar at the top of the app, not the Android button at the bottom. There are a few posts of a similar nature, but they address the back button, not the up button.

Here is the situation: I have an Activity A that has a ListView fragment. When the user clicks on a list view item, it launches Activity B. Pretty typical. Activity A has an EditText field in the toolbar that allows the user to enter a search parameter. If the user hits the up/home button from Activity B, I return successfully to Activity A. However, I want Activity A to show the same text in the EditText field that was there when they left it. If the user hits the back button, this text is restored. But if they navigate with the up/home button, the EditText field is empty.

Using some log statements, I can see that when a list item is tapped from activity A, onSaveInstanceState and onStop are both called (but onDestroy is NOT called at that point.) From activity B, when the up/home button is tapped, onDestroy from activity A is immediately called, followed by onCreate, etc. However, the bundle savedInstanceState is null, presumably since onDestroy was just called.

Why is onDestroy called when returning to Activity A? This makes no sense to me. Here is what I have in the manifest:

<activity
  android:name=".Activity.ActivityA"
  android:label="@string/app_name"
  android:parentActivityName=".Activity.ParentActivity"
  android:theme="@style/AppTheme"
  android:launchMode="singleTop"
  android:windowSoftInputMode="stateVisible" />

<activity
  android:name=".Activity.ActivityB"
  android:label="@string/app_name"
  android:parentActivityName=".Activity.ActivityA"
  android:theme="@style/AppTheme" />

Here are the relevant methods in Activity A:

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_search);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        actionBar = getSupportActionBar();

        if (actionBar != null)
            initializeActionBar();

        if (getSupportActionBar() != null)
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        Log.d(TAG, "on create");

        if (savedInstanceState != null) {
            Log.d(TAG, "saved instance state not null");
            if (savedInstanceState.getString("search_text") != null)
                etSearch.setText(savedInstanceState.getString("search_text"));
        }
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString("search_text", etSearch.getText().toString());
        Log.d(TAG, "on Save instance state");
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);

        Log.d(TAG, "on restore instance state");

        if (savedInstanceState != null) {
            if (savedInstanceState.getString("search_text") != null)
              etSearch.setText(savedInstanceState.getString("search_text"));
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d(TAG, "on resume");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.d(TAG, "on stop");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "on destroy");
    }

private void initializeActionBar() {

    actionBar.setCustomView(R.layout.actionbar_with_edittext);

    etSearch = (EditText) actionBar.getCustomView().findViewById(R.id.actionbar_searchfield);
    etSearch.setOnEditorActionListener(new TextView.OnEditorActionListener() {

        @Override
        public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {

            if(event != null && event.getKeyCode() == KeyEvent.KEYCODE_ENTER && event.getAction() == KeyEvent.ACTION_DOWN) {
                initiateNewSearch();
                etSearch.clearFocus();

            }

            return false;
        }
    });

    InputMethodManager imm = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
    imm.showSoftInput(etSearch, InputMethodManager.SHOW_IMPLICIT);
    etSearch.requestFocus();
}

I don't think that any of the code in Activity B is relevant here.

This is my console output when a user taps on a listview item in Activity A:

on Save instance state
on stop

And then this is what is generated when the user taps on the up/home button from activity B:

on destroy
on create
on resume

If there is anything else that may be of help, please let me know. Thanks for any advice!

回答1:

I don't know why default up button implementation creates a new activity but a working solution for me is to override onOptionsItemSelected:

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    if(id== android.R.id.home ){
        onBackPressed();
        return true;
    }
    return super.onOptionsItemSelected(item);
}

Also this solution works for me:

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home:
                Intent intent = NavUtils.getParentActivityIntent(this);
                intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP
                        | Intent.FLAG_ACTIVITY_SINGLE_TOP);
                NavUtils.navigateUpTo(this, intent);
                return true;
            default:
                break;
        }
        return super.onOptionsItemSelected(item);
    }

回答2:

I had this problem too, and after a little more digging found the correct solution is to make a change in the manifest to add the following to your parent activity:

android:launchMode="singleTop"

Details are explained here.

来源：https://stackoverflow.com/questions/37222278/up-button-calls-ondestroy-of-parent-activity