我一直在尝试添加此切换 5 小时。但它一直告诉drawerLayout为null，这没有任何意义，因为它存在并且我一直在使用它。
package com.example.android.musicalstructure;
import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.content.res.Configuration;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBar;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
public final static int REQUEST_READ_EXTERNAL_STORAGE = 0;
public View tempView;
public String[] mActivitiesDrawer;
public DrawerLayout drawerLayout;
public ListView drawerList;
public ActionBarDrawerToggle drawerToggle;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getPermission();
instantiateDrawer();
setDrawerOnClickListener(1);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);
drawerToggle = new ActionBarDrawerToggle(MainActivity.this, drawerLayout, R.string.open_drawer, R.string.close_drawer) {
public void onDrawerClosed(View view) {
supportInvalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
}
public void onDrawerOpened(View drawerView) {
supportInvalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
}
};
if (drawerLayout != null) {
Log.d("null", "it is not null");
drawerLayout.addDrawerListener(drawerToggle);
drawerToggle.syncState();
}
}
public void instantiateDrawer() {
mActivitiesDrawer = getResources().getStringArray(R.array.drawer_items);
drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
drawerList = (ListView) findViewById(R.id.left_drawer);
//Instantiating an adapter to manage the items for the ListView
drawerList.setAdapter(new ArrayAdapter < String > (this,
R.layout.drawer_list_item, mActivitiesDrawer));
}
public void setDrawerOnClickListener(final int activityNumber) {
drawerList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView <? > adapterView, View view, int i, long l) {
setTempView(view);
Log.d("activityNumber", activityNumber + "and i : " + i);
if (i == activityNumber) {
return;
} else if (i == 0) {
Intent intent = new Intent(getApplicationContext(), AllMusic.class);
startActivity(intent);
} else if (i == 1) {
Intent intent = new Intent(getApplicationContext(), Trending.class);
startActivity(intent);
} else if (i == 2) {
Intent intent = new Intent(getApplicationContext(), Albums.class);
startActivity(intent);
} else if (i == 3) {
Intent intent = new Intent(getApplicationContext(), Playlists.class);
startActivity(intent);
} else {
Intent intent = new Intent(getApplicationContext(), Trending.class);
startActivity(intent);
}
}
});
}
public void getPermission() {
int permissionCheck = ContextCompat.checkSelfPermission(this,
Manifest.permission.READ_EXTERNAL_STORAGE);
if (permissionCheck != PackageManager.PERMISSION_GRANTED) {
if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.READ_EXTERNAL_STORAGE)) {
Toast toast = Toast.makeText(this, "Please accept the permission so the app can access you music files.", Toast.LENGTH_SHORT);
toast.show();
ActivityCompat.requestPermissions(this, new String[] {
Manifest.permission.READ_EXTERNAL_STORAGE
}, REQUEST_READ_EXTERNAL_STORAGE);
} else {
ActivityCompat.requestPermissions(this, new String[] {
Manifest.permission.READ_EXTERNAL_STORAGE
}, REQUEST_READ_EXTERNAL_STORAGE);
}
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
if (drawerToggle.onOptionsItemSelected(item)) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void setTempView(View tempView) {
this.tempView = tempView;
}
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
// Sync the toggle state after onRestoreInstanceState has occurred.
drawerToggle.syncState();
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
drawerToggle.onConfigurationChanged(newConfig);
}
}
这是我的抽屉布局
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.android.musicalstructure.MainActivity">
<!-- The main content view -->
<FrameLayout
android:id="@+id/content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<!-- The navigation drawer -->
<ListView
android:id="@+id/left_drawer"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp"
android:background="#111"/>
</android.support.v4.widget.DrawerLayout>
这是错误日志
07-29 16:45:01.211 14025-14025/com.example.android.musicalstructure E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.musicalstructure, PID: 14025
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.musicalstructure/com.example.android.musicalstructure.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v4.widget.DrawerLayout.isDrawerOpen(int)' 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$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$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 'boolean android.support.v4.widget.DrawerLayout.isDrawerOpen(int)' on a null object reference
at android.support.v7.app.ActionBarDrawerToggle.syncState(ActionBarDrawerToggle.java:239)
at com.example.android.musicalstructure.MainActivity.onPostCreate(MainActivity.java:150)
at android.app.Instrumentation.callActivityOnPostCreate(Instrumentation.java:1188)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2398)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
有人可以帮助我吗，谢谢:)