Question

以下是java代码：

public class Displayprofile extends AppCompatActivity {

    private DrawerLayout mDrawerLayout;
    private ActionBarDrawerToggle mToggle;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.displayprofile);
        mDrawerLayout = (DrawerLayout)findViewById(R.id.drawerlayout) ;
        mToggle = new ActionBarDrawerToggle(this, mDrawerLayout, R.string.open, R.string.close);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        mDrawerLayout.addDrawerListener(mToggle);
        mToggle.syncState();
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if (mToggle.onOptionsItemSelected(item))
        {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

}

导航图标未显示。否则，导航菜单工作正常。只要添加getSupportActionBar().setDisplayHomeAsUpEnabled(true);，应用就会崩溃。只要省略此语句，应用程序就不会崩溃。这项活动的主题如下：

<style name="mainthemered" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="colorAccent">@color/colorLogoRed</item>
</style>

错误如下：

12-06 21:23:11.256 22417-22417/com.example.krsnv.kooc E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.krsnv.kooc, PID: 22417
        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.krsnv.kooc/com.example.krsnv.kooc.Displayprofile}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
            at android.app.ActivityThread.-wrap11(ActivityThread.java)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:148)
            at android.app.ActivityThread.main(ActivityThread.java:5422)
            at java.lang.reflect.Method.invoke(Native Method)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
        Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at com.example.krsnv.kooc.Displayprofile.onCreate(Displayprofile.java:47)
            at android.app.Activity.performCreate(Activity.java:6251)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
            at android.app.ActivityThread.-wrap11(ActivityThread.java) 
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
            at android.os.Handler.dispatchMessage(Handler.java:102) 
            at android.os.Looper.loop(Looper.java:148) 
            at android.app.ActivityThread.main(ActivityThread.java:5422) 
            at java.lang.reflect.Method.invoke(Native Method) 
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Answer 1

设置支持操作栏？

Toolbar myToolbar = (Toolbar) findViewById(R.id.your_toolbar);
setSupportActionBar(myToolbar);
getSupportActionBar().setTitle("Your title");
getSupportActionBar().setDisplayHomeAsUpEnabled(true);

在工具栏上获取导航图标的问题

1 个答案: