android.support.v4.widget.DrawerLayout 无法转换为 android.support.v4.widget.DrawerLayout$DrawerListener

Question

我得到一个 DrawerLayout 无法投射，所以显示错误并且我的应用程序崩溃了。

我是一个新的安卓开发者，帮帮我。

这是我的 MainAvtivity：

public class MainActivity extends AppCompatActivity {

    private Toolbar toolbar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toolbar = (Toolbar) findViewById(R.id.app_bar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayShowHomeEnabled(true);
        NavigationDrawerFragment drawerFragment = (NavigationDrawerFragment)
            getSupportFragmentManager().findFragmentById(R.id.fragment_navigation_drawer);
        drawerFragment.setUp((DrawerLayout) findViewById(R.id.drawer_layout),toolbar);

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

这里是Activitymain.xml：

<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <include
            android:id="@+id/app_bar"
            layout="@layout/app_bar" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/app_bar"

            android:text="@string/hello_world" />

    </RelativeLayout>

    <fragment
        android:id="@+id/fragment_navigation_drawer"
        android:name="com.appdego.rosesketch.NavigationDrawerFragment"
        android:layout_width="@dimen/nav_drawer_width"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:layout="@layout/fragment_navigation_drawer"
        tools:layout="@layout/fragment_navigation_drawer" />

</android.support.v4.widget.DrawerLayout>

我的 NavigationDrawerFragment.java 代码

public class NavigationDrawerFragment extends Fragment {

    private ActionBarDrawerToggle mDrawerToggle;
    private DrawerLayout mDrawerLayout;

    public NavigationDrawerFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_navigation_drawer, container, false);
    }


    public void setUp(DrawerLayout drawerLayout, Toolbar toolbar) {
        mDrawerLayout = drawerLayout;
        mDrawerToggle = new ActionBarDrawerToggle(getActivity(), (DrawerLayout) drawerLayout, toolbar, R.string.drawer_open, R.string.drawer_close) {
            @Override
            public void onDrawerOpened(View drawerView) {
                super.onDrawerOpened(drawerView);
            }

            @Override
            public void onDrawerClosed(View drawerView) {
                super.onDrawerClosed(drawerView);
            }
        };
        mDrawerLayout.setDrawerListener((DrawerListener) mDrawerLayout);
    }

}

和fragment_navigation_drawer.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.appdego.rosesketch.NavigationDrawerFragment">

    <!-- TODO: Update blank fragment layout -->
    <TextView android:layout_width="match_parent" android:layout_height="match_parent"
        android:text="@string/hello_blank_fragment" />

</RelativeLayout>

日志猫：

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.appdego.rosesketch/com.appdego.rosesketch.MainActivity}: java.lang.ClassCastException: android.support.v4.widget.DrawerLayout cannot be cast to android.support.v4.widget.DrawerLayout$DrawerListener
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2338)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
        at android.app.ActivityThread.access$800(ActivityThread.java:151)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
        at android.os.Handler.dispatchMessage(Handler.java:110)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:5292)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:824)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:640)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.ClassCastException: android.support.v4.widget.DrawerLayout cannot be cast to android.support.v4.widget.DrawerLayout$DrawerListener
        at com.appdego.rosesketch.NavigationDrawerFragment.setUp(NavigationDrawerFragment.java:49)
        at com.appdego.rosesketch.MainActivity.onCreate(MainActivity.java:25)
        at android.app.Activity.performCreate(Activity.java:5264)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088)

我遵循 Slidenerd 材料设计教程。

Answer 1

您需要在下面进行代码更改：

  // Set the drawer toggle as the DrawerListener
        mDrawerLayout.setDrawerListener(mDrawerToggle);

Answer 2

问题出在这一行：mDrawerLayout.setDrawerListener((DrawerListener) mDrawerLayout); 您需要设置一个侦听器，但您正在将DrawerLayout 类型转换为DrawerListener。

我建议您完全删除该行，因为它不是必需的。如果你真的想设置一个监听器，你应该这样做：

       mDrawerLayout.setDrawerListener(new DrawerLayout.DrawerListener() {
            @Override
            public void onDrawerSlide(View drawerView, float slideOffset) {

            }

            @Override
            public void onDrawerOpened(View drawerView) {

            }

            @Override
            public void onDrawerClosed(View drawerView) {

            }

            @Override
            public void onDrawerStateChanged(int newState) {

            }
        });