Android Up Navigation Doesn't Work

I'm trying to implement navigation according to: http://developer.android.com/training/implementing-navigation/ancestral.html

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    // Respond to the action bar's Up/Home button
    case android.R.id.home:
        Intent upIntent = NavUtils.getParentActivityIntent(this);
        if (NavUtils.shouldUpRecreateTask(this, upIntent)) {
            // This activity is NOT part of this app's task, so create a new task
            // when navigating up, with a synthesized back stack.
            TaskStackBuilder.create(this)
                    // Add all of this activity's parents to the back stack
                    .addNextIntentWithParentStack(upIntent)
                    // Navigate up to the closest parent
                    .startActivities();
        } else {
            // This activity is part of this app's task, so simply
            // navigate up to the logical parent activity.
            NavUtils.navigateUpTo(this, upIntent);
        }
        return true;
    }
    return super.onOptionsItemSelected(item);
}

but if (NavUtils.shouldUpRecreateTask(this, upIntent)) { is returning FALSE always.

How is this code useful? In which cases it does return true?

---

On pre-Jelly Bean devices, per the source code of NavUtils, shouldUpRecreateTask is:

public boolean shouldUpRecreateTask(Activity activity, Intent targetIntent) {
    String action = activity.getIntent().getAction();
    return action != null && !action.equals(Intent.ACTION_MAIN);
}

Which uses the Activity 's action (ie, ACTION_VIEW , etc.) to determine if this Activity was launched from an external source. On Jelly Bean+ devices, it uses Activity.shouldUpRecreateTask (source code):

public boolean shouldUpRecreateTask(Intent targetIntent) {
    try {
        PackageManager pm = getPackageManager();
        ComponentName cn = targetIntent.getComponent();
        if (cn == null) {
            cn = targetIntent.resolveActivity(pm);
        }
        ActivityInfo info = pm.getActivityInfo(cn, 0);
        if (info.taskAffinity == null) {
            return false;
        }
        return !ActivityManagerNative.getDefault()
                .targetTaskAffinityMatchesActivity(mToken, info.taskAffinity);
    } catch (RemoteException e) {
        return false;
    } catch (NameNotFoundException e) {
        return false;
    }
}

Which uses Task Affinity to determine if the given Activity 's affinity is the same as the affinity it was launched with (ie, if Gmail launches your Activity , it would be given Gmail's affinity, rather than its own).

NavUtils.navigateUpTo , in all cases, launches an Activity. If it isn't launching the appropriate Activity , then you may need to look at what launch mode you are using and provide details on what platform version it isn't working.

---

I solved it by using the ActivityManager and checking for the backStack entries.

I hope it will be usefull for you all.

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:

            ActivityManager am = (ActivityManager) getApplicationContext().getSystemService(getApplicationContext().ACTIVITY_SERVICE);
            List<RunningTaskInfo> runningTaskInfoList =  am.getRunningTasks(10);
            List<String> backStack = new ArrayList<String>();
            Iterator<RunningTaskInfo> itr = runningTaskInfoList.iterator();
            while(itr.hasNext()){
                RunningTaskInfo runningTaskInfo = (RunningTaskInfo)itr.next();
                String topActivity = runningTaskInfo.topActivity.getShortClassName();
                backStack.add(topActivity.trim());
            }
            if(backStack!=null){
                if(backStack.get(1).equals(".MainActivity")){
                    moveTaskToBack(true); // or finish() if you want to finish it. I don't.
                } else {
                    Intent intent = new Intent(this, MainActivity.class);
                    intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                    startActivity(intent);
                    finish();
                }
            }

        break;  
    }
}

And I needed to use:

<uses-permission android:name="android.permission.GET_TASKS" />

in my Manifest.

It works perfectly, though it's not the solution I would have wanted. Unfortunately, android is still lacking of advanced built-in methods to achieve simple things, and we all have to find the way of everything.

链接地址: http://www.djcxy.com/p/72470.html

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