How to resume activity instead of restart when going “up” from action bar

问题

I have two activities. Say Activity A and Activity B.
From Activity A I click a button to launch Activity B This is the code I use for this:

Intent intent = new Intent(this, ActivityB.class);
this.startActivity(intent);

Now at this point, I am in Activity B. On the on create method of Activity B, I enable the up button.

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_view_news);

    getActionBar().setDisplayHomeAsUpEnabled(true); //Here//
}

and on the event handle for the "up" button, i have this code:

public boolean onOptionsItemSelected(MenuItem item){
     switch (item.getItemId()) {
        case android.R.id.home:
            finish();
            NavUtils.navigateUpFromSameTask(this);
        default:
            return super.onOptionsItemSelected(item);
    }
}

Now I decide to go back to Activity A I click the up button in the action bar which looks like this:

Now the problem is, when I click the "up button", it goes back to Activity A which is fine, but it restarts it. How can make it stop restarting? I just want it to resume.

When I use my hardware back button, it works as expected. i.e it goes to Activity A and resumes it instead of restarting it.

I want my activity to resume because on that activity, I download some string online and so I don't want it to keep re downloading the data when a users goes from Activity B -> Activity A

Edit My manifest file for Activity B section looks like this:

<activity
    android:name="com.example.android.ActivityB"
    android:label="@string/title_activity_view_news"
    android:parentActivityName="com.example.android.ActivityA">
    <meta-data
        android:name="android.support.PARENT_ACTIVITY"
        android:value="com.example.android.ActivityA" />
</activity>

Edit 2 [Answer] Ok so, this was pretty unexpected but in my AndroidManifest.xml, in the Activity A section, I had to add the following line liner. android:launchMode="singleTop" so it now looks like this:

<activity
    android:name="com.example.android.ActivityA"
    android:label="@string/app_name" 
    android:launchMode="singleTop"> //**HERE**//
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />

        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

The explanation to this is given here

回答1:

Should've added as an answer instead of a comment.. but here you go so you can accept if you want so others can see if necessary.

https://stackoverflow.com/a/16147110/3286163

Basically, to summarize the android will always recreate the activity unless you specify it not to with

android:launchMode="singleTop"

Note: it will not work if the returning activity is not on the top of the back stack as mentioned in the reference.

For anyone else, please upvote the answer in the url instead of mine if you find this useful.

回答2:

You can also achieve the same outcome programatically

Intent upIntent = NavUtils.getParentActivityIntent(this);
upIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
NavUtils.navigateUpTo(this, upIntent);

来源：https://stackoverflow.com/questions/21805382/how-to-resume-activity-instead-of-restart-when-going-up-from-action-bar

标签

android

android-actionbar

android-navigation