为此，可以采用两种方式:XML或Java。看这里:如何更改操作栏上的文本

So:

XML:

<activity android:name=".Hello_World"
              android:label="This is the Hello World Application">
</activity>

Java:

public class TitleBar extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);

       final boolean customTitleSupported = requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);

       setContentView(R.layout.main);


       if ( customTitleSupported ) {
           getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.titlebar);
           }

       final TextView myTitleText = (TextView) findViewById(R.id.myTitle);
       if ( myTitleText != null ) {
           myTitleText.setText("NEW TITLE");

           // user can also set color using "Color" and then "Color value constant"
          // myTitleText.setBackgroundColor(Color.GREEN);
       }
 }
}

为此，可以采用两种方式:XML或Java。看这里:如何更改操作栏上的文本

So:

XML:

<activity android:name=".Hello_World"
              android:label="This is the Hello World Application">
</activity>

Java:

public class TitleBar extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);

       final boolean customTitleSupported = requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);

       setContentView(R.layout.main);


       if ( customTitleSupported ) {
           getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.titlebar);
           }

       final TextView myTitleText = (TextView) findViewById(R.id.myTitle);
       if ( myTitleText != null ) {
           myTitleText.setText("NEW TITLE");

           // user can also set color using "Color" and then "Color value constant"
          // myTitleText.setBackgroundColor(Color.GREEN);
       }
 }
}

你也可以这样做:

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main2)
        setSupportActionBar(toolbar)
        setTitle("Activity 2")
    }

在Android 5.0中，材料设计指南不鼓励在actionBar中使用图标

要启用它，请添加以下代码

getSupportActionBar().setDisplayShowHomeEnabled(true);
getSupportActionBar().setLogo(R.mipmap.ic_launcher);
getSupportActionBar().setDisplayUseLogoEnabled(true);

功劳归于这篇文章的作者

这很容易做到

如果你想在代码中改变它，调用:

setTitle("My new title");
getActionBar().setIcon(R.drawable.my_icon);

并将值设置为您喜欢的任何值。

或者，在Android manifest XML文件中:

<activity android:name=".MyActivity" 
       android:icon="@drawable/my_icon" 
       android:label="My new title" />  

要在应用程序中启用后退按钮，请使用:

 getActionBar().setHomeButtonEnabled(true);
 getActionBar().setDisplayHomeAsUpEnabled(true);

代码应该全部放在onCreate中，这样标签/图标的变化对用户是透明的，但实际上它可以在活动生命周期的任何地方被调用。

我在onNavigationItemSelected内部使用了以下调用:

HomeActivity.this.setTitle(item.getTitle());