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我的NavigationView onClick事件无法正常工作.

以下是我逐个尝试的代码片段,但没有任何效果:

1. 使用OnClick()方法实现NavigationView.OnNavigationItemSelectedListener

2. 设置NavigationItemSelectedListener方法

   nav  = (NavigationView)findViewById(R.id.nav);
   nav.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
       @Override
       public boolean onNavigationItemSelected(MenuItem item) {
           Toast.makeText(getApplicationContext(),"Hello",Toast.LENGTH_SHORT).show();
           return true;
       }
   });
   

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3. 使用OnOptionItemSelected方法

   @Override
   public boolean onOptionsItemSelected(MenuItem item) {
   if(toggle.onOptionsItemSelected(item))
   {
       return true;
   }
   switch (item.getItemId()) {
       case R.id.lib:
   
           Toast.makeText(getApplicationContext(),"OK",Toast.LENGTH_SHORT).show();
           return true;
   
       case R.id.fav:
           Toast.makeText(getApplicationContext(),"OK",Toast.LENGTH_SHORT).show();
   
           return true;
   }
   return super.onOptionsItemSelected(item);
   }
   

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我也尝试了所有这些与我的问题相关的问题和博客,但它没有用.

1. 导航抽屉:setNavigationItemSelectedListener不起作用.
2. NavigationView:setNavigationItemSelectedListener
3. onNavigationItemSelected在NavigationView中不起作用

这是我的Complete MainActivity.java文件

public class MainActivity extends AppCompatActivity{

public frag_song song;
public frag_artist artist;
public  frag_album album;
public TabLayout tab;
Uri songUri;
Cursor songCursor;
public static …

在将问题标记为重复之前，请先阅读问题...

所以我尝试使用 Intent 从图库中选择多个图像。当我选择超过 1 个图像时，它可以正常工作，而当我仅选择 1 个图像时，它会生成此错误。我查找了每个 NullPointer 异常问题，但没有成功。

FATAL EXCEPTION: main
              Process: com.blackhat.applocker, PID: 1892
              java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=2, result=-1, data=Intent { dat=content://com.android.providers.media.documents/document/image:10227 flg=0x1 }} to activity {com.blackhat.applocker/com.blackhat.applocker.ProtactGallery}: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.ClipData.getItemCount()' on a null object reference
                  at android.app.ActivityThread.deliverResults(ActivityThread.java:3839)
                  at android.app.ActivityThread.handleSendResult(ActivityThread.java:3882)
                  at android.app.ActivityThread.access$1300(ActivityThread.java:178)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1519)
                  at android.os.Handler.dispatchMessage(Handler.java:111)
                  at android.os.Looper.loop(Looper.java:194)
                  at android.app.ActivityThread.main(ActivityThread.java:5637)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at java.lang.reflect.Method.invoke(Method.java:372)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
                  at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:114)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method …