Recyclerview的適配器上的空指針異常

Question

我是Android初學者，我試圖在Android中製作簡單的回收站視圖。 但在適配器類上顯示錯誤。請幫我解決。

我的主要活動：

recycle_view.java：

package h.safmical.swipe; 

    import android.os.Bundle; 
    import android.support.annotation.Nullable; 
    import android.support.v7.app.AppCompatActivity; 
    import android.support.v7.widget.LinearLayoutManager; 
    import android.support.v7.widget.RecyclerView; 

    import java.util.ArrayList; 
    import java.util.List; 



    public class recycle_view extends AppCompatActivity{ 
     private RecyclerView recyclerView; 
     private recycle_view_adapter adapter; 
     @Override 
     protected void onCreate(@Nullable Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      recyclerView= (RecyclerView) findViewById(R.id.recycleview); 
      adapter = new recycle_view_adapter(this,getData()); 
      recyclerView.setAdapter(adapter); 
      recyclerView.setLayoutManager(new LinearLayoutManager(this)); 
     } 
     public static List<recycle_view_information> getData(){ 
      List<recycle_view_information> data=new ArrayList<>(); 
      int[] icons={R.drawable.my}; 
      String[] titles={"Harsh"}; 
      for (int i=0;i<icons.length && i<titles.length;i++){ 
       recycle_view_information current=new recycle_view_information(); 
       current.iconid=icons[i]; 
       current.title=titles[i]; 
       data.add(current); 

      } 
      return data; 
     } 
    } 

適配器回收視圖：

recycle_view_adapter.java：

package h.safmical.swipe; 

import android.content.Context; 
import android.support.v7.widget.RecyclerView; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ImageView; 
import android.widget.TextView; 

import java.util.Collections; 
import java.util.List; 



    public class recycle_view_adapter extends RecyclerView.Adapter<recycle_view_adapter.MyViewHolder> { 

     private LayoutInflater inflater; 
     List<recycle_view_information> data= Collections.emptyList(); 


     public recycle_view_adapter(Context context,List<recycle_view_information> data){ 
      inflater=LayoutInflater.from(context); 
     } 



     @Override 
     public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
      View view=inflater.inflate(R.layout.recycle_view_custom_row,parent,false); 
      MyViewHolder holder=new MyViewHolder(view); 
      return holder; 
     } 

     @Override 
     public void onBindViewHolder(MyViewHolder holder, int position) { 

      recycle_view_information current=data.get(position); 
      holder.title.setText(current.title); 
      holder.icon.setImageResource(current.iconid); 
     } 

     @Override 
     public int getItemCount() { 
      return 0; 
     } 
     class MyViewHolder extends RecyclerView.ViewHolder{ 
      TextView title; 
      ImageView icon; 

      public MyViewHolder(View itemView) { 
       super(itemView); 
       title= (TextView) itemView.findViewById(R.id.text); 
       icon= (ImageView) itemView.findViewById(R.id.image); 
      } 
     } 
    } 

recycle_view_information.java：

package h.safmical.swipe; 
    public class recycle_view_information { 
     int iconid; 
     String title; 
    } 

我的XML文件： recycle_view.xml：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:orientation="vertical" android:layout_width="match_parent" 
    android:layout_height="match_parent"> 
<android.support.v7.widget.RecyclerView 
    android:id="@+id/recycleview" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent"> 
</android.support.v7.widget.RecyclerView> 
</LinearLayout> 

recycle_view_custom_row.xml：

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" android:layout_height="match_parent"> 

    <ImageView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:id="@+id/image" 
     android:src="@mipmap/ic_launcher_round"/> 
    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:id="@+id/text" 
     android:text="dummy" 
     android:layout_toRightOf="@+id/image" 
     android:layout_marginTop="15dp" 
     /> 

</RelativeLayout> 

錯誤的logcat：

06-15 15:03:38.904 8891-8891/h.safmical.swipe E/AndroidRuntime: FATAL EXCEPTION: main 
                   Process: h.safmical.swipe, PID: 8891 
                   java.lang.RuntimeException: Unable to start activity ComponentInfo{h.safmical.swipe/h.safmical.swipe.recycle_view}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setAdapter(android.support.v7.widget.RecyclerView$Adapter)' on a null object reference 
                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2426) 
                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490) 
                    at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354) 
                    at android.os.Handler.dispatchMessage(Handler.java:102) 
                    at android.os.Looper.loop(Looper.java:148) 
                    at android.app.ActivityThread.main(ActivityThread.java:5443) 
                    at java.lang.reflect.Method.invoke(Native Method) 
                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728) 
                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setAdapter(android.support.v7.widget.RecyclerView$Adapter)' on a null object reference 
                    at h.safmical.swipe.recycle_view.onCreate(recycle_view.java:24) 
                    at android.app.Activity.performCreate(Activity.java:6245) 
                    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130) 
                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379) 
                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)  
                    at android.app.ActivityThread.-wrap11(ActivityThread.java)  
                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)  
                    at android.os.Handler.dispatchMessage(Handler.java:102)  
                    at android.os.Looper.loop(Looper.java:148)  
                    at android.app.ActivityThread.main(ActivityThread.java:5443)  
                    at java.lang.reflect.Method.invoke(Native Method)  
                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)  
                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)  

Answer 1

你錯過onCreate

setContentView(R.layout.activity_recyclerview); 

Answer 2

此行您還沒有設置您的活動的看法。

寫您的活動的onCreate方法

setContentView(R.layout.recycle_view.xml)