列表視圖使Android應用崩潰

Question

我正在研究與健康相關的Android應用。在此，我使用IndexPage.java中的浮動操作按鈕切換到另一個活動FoodEntry.java（具有食品項目的列表視圖）。在這個每當我們點擊浮動按鈕的應用程序崩潰。有一件事我發現應用程序由於listview而崩潰。請幫我找到解決辦法。

這是IndexPage.java

public class IndexPage extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_index_page); 
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
    fab.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 

      Intent in = new Intent(IndexPage.this, FoodEntry.class); 
      startActivity(in); 

     } 
    }); 
} 
} 

FoodEntry.java

public class FoodEntry extends AppCompatActivity { 

// Array of strings... 
String[] food = {"Naan","Pav bhaji","chole tikiya", "rice", "soyabean", "milk", "curd", "abc", "def", "dfadf", "fasdfa", "fsadf", "fdsfa", "fga"}; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 


    ArrayAdapter adapter = new ArrayAdapter<>(this, R.layout.activity_item, food); 
    ListView listViewFoodItems = (ListView)findViewById(R.id.listViewFood); 
    listViewFoodItems.setAdapter(adapter); 
} } 

上logcat的錯誤

03-31 15:30:58.555 13732-13732/com.praval.healthfreak W/dalvikvm: threadid=1: calling UncaughtExceptionHandler 
03-31 15:30:58.556 13732-13732/com.praval.healthfreak E/AndroidRuntime: FATAL EXCEPTION: main 
                     Process: com.praval.healthfreak, PID: 13732 
                     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.praval.healthfreak/com.praval.healthfreak.FoodEntry}: java.lang.NullPointerException 
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2389) 
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2441) 
                      at android.app.ActivityThread.access$900(ActivityThread.java:151) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354) 
                      at android.os.Handler.dispatchMessage(Handler.java:110) 
                      at android.os.Looper.loop(Looper.java:193) 
                      at android.app.ActivityThread.main(ActivityThread.java:5345) 
                      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:828) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:644) 
                      at dalvik.system.NativeStart.main(Native Method) 
                     Caused by: java.lang.NullPointerException 
                      at com.praval.healthfreak.FoodEntry.onCreate(FoodEntry.java:20) 
                      at android.app.Activity.performCreate(Activity.java:5343) 
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088) 
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2343) 
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2441)  
                      at android.app.ActivityThread.access$900(ActivityThread.java:151)  
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)  
                      at android.os.Handler.dispatchMessage(Handler.java:110)  
                      at android.os.Looper.loop(Looper.java:193)  
                      at android.app.ActivityThread.main(ActivityThread.java:5345)  
                      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:828)  
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:644)  
                      at dalvik.system.NativeStart.main(Native Method) 

Answer 1

您忘記添加

setContentView(R.layout.activity_layout); 

在FoodEntry Activity