setBar运行时错误setOnRatingBarChangeListener

Question

我的目标是从评级栏获取值并存储并显示值。

我有下面的代码在我onClickMethod

rb = (RatingBar) findViewById(R.id.ratingBar); 
    result = (TextView) findViewById(R.id.lblResult); 

    rb.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener() { 
     @Override 
     public void onRatingChanged(RatingBar ratingBar, float rating, boolean fromUser) { 

     } 
    }); 

它给我的错误在这条线 rb.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener()

的logcat：

11-19 18:12:10.328 8654-8654/tanav.sharma E/AndroidRuntime: FATAL EXCEPTION: main 
Process: tanav.sharma, PID: 8654 
java.lang.RuntimeException: Unable to start activity ComponentInfo{tanav.sharma/tanav.sharma.TanavActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RatingBar.setOnRatingBarChangeListener(android.widget.RatingBar$OnRatingBarChangeListener)' on a null object reference 
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3319) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
    at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:148) 
    at android.app.ActivityThread.main(ActivityThread.java:7331) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RatingBar.setOnRatingBarChangeListener(android.widget.RatingBar$OnRatingBarChangeListener)' on a null object reference 
    at tanav.sharma.TanavActivity.onCreate(TanavActivity.java:101) 
    at android.app.Activity.performCreate(Activity.java:6904) 
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136) 
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3266) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)  
    at android.app.ActivityThread.access$1100(ActivityThread.java:229)  
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)  
    at android.os.Handler.dispatchMessage(Handler.java:102)  
    at android.os.Looper.loop(Looper.java:148)  
    at android.app.ActivityThread.main(ActivityThread.java:7331)  
    at java.lang.reflect.Method.invoke(Native Method)  
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)  
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)  

---

的.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" 
    android:padding="16dp" 
    tools:context="tanav.sharma.OneFragment"> 

    <LinearLayout 
     android:id="@+id/name_id" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:orientation="horizontal"> 

     <TextView 
      android:layout_width="180dp" 
      android:layout_height="wrap_content" 
      android:text="@string/fname" 
      android:textSize="20dp" 
      android:textStyle="bold" 
      android:layout_centerInParent="true"/> 

     <TextView 
      android:layout_width="140dp" 
      android:layout_height="wrap_content" 
      android:text="@string/sid" 
      android:textAlignment="textEnd" 
      android:textSize="20dp" 
      android:textStyle="bold" 
      android:layout_centerInParent="true"/> 
    </LinearLayout> 

    <LinearLayout 
     android:padding="16dp" 
     android:id="@+id/counter_display" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:orientation="horizontal" 
     android:layout_below="@+id/name_id"> 

     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="Counter: " 
      android:layout_gravity="left|center_vertical" /> 

     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="" 
      android:id="@+id/counter" 
      /> 

    </LinearLayout> 

    <LinearLayout 
     android:id="@+id/five_star" 
     android:padding="10dp" 
     android:layout_centerHorizontal="true" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/counter_display"> 

     <RatingBar 
      android:id="@+id/ratingBar" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:numStars="5" 
      android:stepSize="0.5" 
      android:rating="5.0" 
      /> 

    </LinearLayout> 

    <RelativeLayout 
     android:id="@+id/download_button" 
     android:layout_below="@+id/five_star" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     > 

     <Button 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
      android:id="@+id/download_image" 
      android:text="@string/download" 
      /> 

     <ImageView 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" /> 


    </RelativeLayout> 




</RelativeLayout> 

以下文件是java文件（即MainActivity.java）

public class TanavActivity extends AppCompatActivity { 

    RatingBar rb; 
    TextView result; 

    private Toolbar toolbar; 
    private TabLayout tabLayout; 
    private ViewPager viewPager; 
    private int[] tabIcons = { 
      R.drawable.ic_action_pro, 
      R.drawable.ic_action_web 
    }; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_tanav); 


     toolbar = (Toolbar)findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 

     /** 
     * This button is responsible for taking the user back 
     * to the main activity. Preventing the user from pressing 
     * the back key multiple times. 
     */ 
     getSupportActionBar().setDisplayHomeAsUpEnabled(true); 

     viewPager = (ViewPager)findViewById(R.id.viewpager); 
     setupViewPager(viewPager); 

     tabLayout = (TabLayout)findViewById(R.id.tabs); 
     tabLayout.setupWithViewPager(viewPager); 
     setupTabIcons(); 

     tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() { 

      int count_image = 0; 
      int count_web = 0; 
      @Override 
      public void onTabSelected(TabLayout.Tab tab) { 
       int position = tab.getPosition(); 
       if(position == 0){ 

        count_image = count_image + 1; 
        TextView counter = (TextView) findViewById(R.id.counter); 
        counter.setText(Integer.toString(count_image)); 

       }else if(position == 1){ 
        //count_web = count_web + 1; 
       } 
      } 

      @Override 
      public void onTabUnselected(TabLayout.Tab tab) { 

      } 

      @Override 
      public void onTabReselected(TabLayout.Tab tab) { 
       count_image = count_image + 1; 
       TextView counter = (TextView) findViewById(R.id.counter); 
       counter.setText(Integer.toString(count_image)); 
      } 
     }); 

     rb = (RatingBar) findViewById(R.id.ratingBar); 
     result = (TextView) findViewById(R.id.lblResult); 

     rb.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener() { 
      @Override 
      public void onRatingChanged(RatingBar ratingBar, float rating, boolean fromUser) { 

      } 
     }); 

    } 

Answer 1

一切似乎是正确的。 您的内容视图必须有错误。 确保这是你的xml。使用具有ratingBar ID的xml文件名更改它。

setContentView(R.layout.activity_tanav);