是否真的需要编写Java代码来显示Android中的“向上导航”按钮？

Question

When I want to provide Up Navigation in the ActionBar of an Android activity, I just write these lines of code in the AndroidManifest.xml:

<activity android:name=".SettingsActivity"
    android:parentActivityName=".MainActivity">
    <meta-data
        android:name="android.support.PARENT_ACTIVITY"
        android:value=".MainActivity"/>
</activity>

However, now I've just saw these lines of code in the java file:

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

    ActionBar actionBar = this.getSupportActionBar();

    if (actionBar != null) {
        actionBar.setDisplayHomeAsUpEnabled(true);
    }
}

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

All my previous projects just worked without the these lines of Java. Are they really necessary? If they are, are they necessary for compatibility for android versions? In this case, previous to which version?

Answer 1

You should be using Appcompat which is a compatibility library to access and customize different ui elements known as views on api 7<= . When you override " onOptionsItemSelected ", you add a custom action to a button on the action bar (so now isnthe implementation of NavUtils.navigateUpFromSameTask(this) ). So let your activity extend AppCompatActivity (if it isn't already).