空指針異常 - Android片段中的按鈕

目前我正在研究Android中片段和Activity之間的通信。我想在這裏實現的是在Fragment中的一個按鈕上設置onClickListener。然而，NPE發生了，我找不到原因。在堆棧流程中有很多類似的問題，但我沒有找到適合我的工具。以下是我的代碼和logcat。已經在這裏呆了一段時間，希望有人能幫助我！空指針異常 - Android片段中的按鈕

的logcat：

> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity 
> ComponentInfo{com.example.ivylin.corewar/com.example.ivylin.corewar.assistantWidgets.WarriorBattleSelfScreen}: 
> android.view.InflateException: Binary XML file line #7: Error 
> inflating class fragment 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.access$800(ActivityThread.java:144) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:102) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:135) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5221) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Native Method) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:372) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: Caused by: android.view.InflateException: Binary XML file line #7: Error 
> inflating class fragment 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:763) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.view.LayoutInflater.rInflate(LayoutInflater.java:806) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.view.LayoutInflater.inflate(LayoutInflater.java:504) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.view.LayoutInflater.inflate(LayoutInflater.java:414) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.view.LayoutInflater.inflate(LayoutInflater.java:365) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:256) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at com.example.ivylin.corewar.assistantWidgets.WarriorBattleSelfScreen.onCreate(WarriorBattleSelfScreen.java:36) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.Activity.performCreate(Activity.java:5933) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.access$800(ActivityThread.java:144)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:102)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:135)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5221)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Native Method)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:372)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void 
> android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' 
> on a null object reference 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at com.example.ivylin.corewar.assistantWidgets.WarriorBattleFragment.onCreateView(WarriorBattleFragment.java:46) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.Fragment.performCreateView(Fragment.java:2053) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:870) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1045) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.FragmentManagerImpl.addFragment(FragmentManager.java:1147) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2116) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.Activity.onCreateView(Activity.java:5282) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.support.v4.app.BaseFragmentActivityHoneycomb.onCreateView(BaseFragmentActivityHoneycomb.java:34) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:79) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:733) 
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.view.LayoutInflater.inflate(LayoutInflater.java:504)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.view.LayoutInflater.inflate(LayoutInflater.java:414)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.view.LayoutInflater.inflate(LayoutInflater.java:365)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:256)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at com.example.ivylin.corewar.assistantWidgets.WarriorBattleSelfScreen.onCreate(WarriorBattleSelfScreen.java:36)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.Activity.performCreate(Activity.java:5933)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.access$800(ActivityThread.java:144)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:102)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:135)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5221)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Native Method)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:372)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)  
>  04-14 17:53:02.163 15136-15136/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

看來，logcat的主要告訴按鈕BOK爲空。查看下面的詳細代碼。

我的片段：

public class WarriorBattleFragment extends Fragment implements View.OnClickListener { 
private RecyclerView recyclerView; 
private WarriorBattleAdapter adapter; 

EditText nP1; 
EditText nP2; 
Button bStart; 
static private int click; 

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

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstance) { 
    View layout = inflater.inflate(R.layout.activity_warrior_self_battle_recyclerview, container, false); 
    recyclerView = (RecyclerView) layout.findViewById(R.id.recycler_view); 
    LinearLayoutManager layoutManager; 

    bStart = (Button) recyclerView.findViewById(R.id.bOK); 
    nP1 = (EditText) recyclerView.findViewById(R.id.nP1); 
    nP2 = (EditText) recyclerView.findViewById(R.id.nP2); 
    bStart.setOnClickListener(this); 

    layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false); 
    recyclerView.setLayoutManager(layoutManager); 
    adapter = new WarriorBattleAdapter(getActivity()); 
    recyclerView.setAdapter(adapter); 
    return layout; 
} 


@Override 
public void onClick(View v) { 
    switch (v.getId()) { 
     case R.id.bStart: 
      if (UserInformation.selectedBW[0].equals("") && UserInformation.selectedBW[1].equals("")) { 
       Toast.makeText(getActivity().getApplicationContext(), "Please Choose A Warrior", Toast.LENGTH_SHORT).show(); 
      } else { 
       click++; 
       if (click == 1) { 
        nP1.setText(UserInformation.selectedBW[0]); 
        adapter.setAdded(1); 
       } else if (click == 2) { 
        bStart.setText("BATTLE!"); 
       } else if (click == 3) { 
        Toast.makeText(getActivity().getApplicationContext(), "WARRIOR FILES UPLOADING", Toast.LENGTH_SHORT).show(); 
       } 
      } 
      if (!UserInformation.selectedBW[0].equals("")) { 
       Intent intent = new Intent(getActivity().getApplicationContext(), DemoDisplay.class); 
       intent.putExtra("wName", UserInformation.selectedBW[0]); 
       intent.putExtra("MODE", UserInformation.selectedBW[0]); 
       startActivity(intent); 

      } else { 
       Toast.makeText(getActivity().getApplicationContext(), "Please select one warrior", Toast.LENGTH_SHORT).show(); 
      } 
      break; 
    } 

} 
}

我的活動：

public class WarriorBattleSelfScreen extends AppCompatActivity implements View.OnClickListener { 
Button bBack; 
Intent intent; 
static int click; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    // set to full screen 
    requestWindowFeature(Window.FEATURE_NO_TITLE); 
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN); 

    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_warrior_battle_self_screen); 
    bBack = (Button) findViewById(R.id.bBack); 

    // THIS PART IS FOR TEST 
    UserInformation.empty = false; 
    WarriorCardEntity imp = new WarriorCardEntity(); 
    imp.title = "Imp"; 
    imp.image = R.drawable.w9; 
    UserInformation.dataContainer.put(0, imp); 
    WarriorCardEntity rave = new WarriorCardEntity(); 
    rave.title = "Rave"; 
    rave.image = R.drawable.w10; 
    UserInformation.dataContainer.put(1, rave); 
    WarriorCardEntity lin = new WarriorCardEntity(); 
    lin.title = "lin"; 
    lin.image = R.drawable.w20; 
    UserInformation.dataContainer.put(2, lin); 

    bBack.setOnClickListener(this); 
} 

@Override 
public void onClick(View v) { 
    switch (v.getId()) { 
     case R.id.bBack: 
      finish(); 
      break; 
    } 
} 
}

XML片段中：

activity_warrior_self_battle_recyclerview 

<?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" 
    android:fitsSystemWindows="true" 
    android:screenOrientation="landscape" 
    > 

    <RelativeLayout 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:layout_centerInParent="true"> 

     <android.support.v7.widget.RecyclerView 
      android:id="@+id/recycler_view" 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:layout_alignParentBottom="true"> 
     </android.support.v7.widget.RecyclerView> 


     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="P1: " 
      android:textSize="20sp" 
      android:textColor="@color/white" 
      android:id="@+id/tP1" 
      /> 
     <EditText 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:id="@+id/nP1" 
      android:layout_toRightOf="@+id/tP1" 
      android:hint="WARRIOR1" 
      android:textColor="@color/white" 
      android:textColorHint="@color/white"/> 

     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="P2: " 
      android:layout_marginLeft="400dp" 
      android:textSize="20sp" 
      android:textColor="@color/white" 
      android:id="@+id/tP2" 
      /> 
     <EditText 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:id="@+id/nP2" 
      android:layout_toRightOf="@+id/tP2" 
      android:layout_alignParentRight="true" 
      android:hint="WARRIOR2" 
      android:textColor="@color/white" 
      android:textColorHint="@color/white"/> 

     <Button 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="OK" 
      android:background="@drawable/button" 
      android:textColor="@color/white" 
      android:id="@+id/bOK" 
      android:layout_marginRight="33dp" 
      android:layout_marginEnd="33dp" 
      android:layout_marginBottom="0dp" 
      android:layout_alignParentBottom="true" 
      android:layout_alignParentRight="true" 
      android:layout_alignParentEnd="true" /> 


    </RelativeLayout> 
</RelativeLayout>

XML在Activity-- activity_warrior_battle_self_screen

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:screenOrientation="landscape" 
    android:background="@drawable/background_gene"> 

    <fragment class="com.example.ivylin.corewar.assistantWidgets.WarriorBattleFragment" 
     android:id="@+id/b_self_fragment" 
     android:layout_width="match_parent" 
     android:layout_height="320dp" 
     android:layout_centerVertical="true" 
     android:layout_toRightOf="@+id/Add" 
     android:layout_toEndOf="@+id/Add" 
     android:layout_marginLeft="30dp" /> 

    <Button 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Back" 
     android:background="@drawable/button" 
     android:textColor="@color/white" 
     android:id="@+id/bBack" 
     android:layout_marginLeft="33dp" 
     android:layout_marginStart="33dp" 
     android:layout_marginBottom="20dp" 
     android:layout_alignParentBottom="true" 
     android:layout_alignParentLeft="true" 
     android:layout_alignParentStart="true" /> 

</RelativeLayout>

來源

2016-04-14 Ivy Lin

你呼籲RecyclerView findViewById()。

你需要調用它放在你的根視圖來代替：

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstance) { 
    View layout = inflater.inflate(R.layout.activity_warrior_self_battle_recyclerview, container, false); 
    recyclerView = (RecyclerView) layout.findViewById(R.id.recycler_view); 
    LinearLayoutManager layoutManager; 


    //change to layout.findViewById(): 
    bStart = (Button) layout.findViewById(R.id.bOK); //modified 
    nP1 = (EditText) layout.findViewById(R.id.nP1); //modified 
    nP2 = (EditText) layout.findViewById(R.id.nP2); //modified 
    bStart.setOnClickListener(this); 

    layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false); 
    recyclerView.setLayoutManager(layoutManager); 
    adapter = new WarriorBattleAdapter(getActivity()); 
    recyclerView.setAdapter(adapter); 
    return layout; 
}

來源

2016-04-14 22:49:05

是的，您致電recyclerView.findViewById(R.id.bOK);返回null。這是因爲您的ViewGroup recyclerView中沒有帶ID「bOK」的按鈕，其中您試圖找到帶有findViewById()的按鈕。

在佈局你打開和關閉RecyclerView標籤瞬間：

<android.support.v7.widget.RecyclerView 
    android:id="@+id/recycler_view" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:layout_alignParentBottom="true"> 
</android.support.v7.widget.RecyclerView>

這可能只是偶然的。你不應該關閉的標籤，直到你的按鈕後，這樣的 - 如果按鈕應該在RecyclerView：

<Button 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="OK" 
      android:background="@drawable/button" 
      android:textColor="@color/white" 
      android:id="@+id/bOK" 
      android:layout_marginRight="33dp" 
      android:layout_marginEnd="33dp" 
      android:layout_marginBottom="0dp" 
      android:layout_alignParentBottom="true" 
      android:layout_alignParentRight="true" 
      android:layout_alignParentEnd="true" /> 

</android.support.v7.widget.RecyclerView>

來源

2016-04-14 22:48:20

你應該@Micha作出適當修改您的代碼，每個答案和@Daniel

但

日誌描繪完全不同的問題 -

您已設置屬性android:screenOrientation="landscape"父RelativeLayout在activity_warrior_self_battle_recyclerview.xml

這是不正確，因爲 android:screenOrientation不是RelativeLayout有效的機器人屬性。

來源

2016-04-14 23:07:20

空指針異常 - Android片段中的按鈕

回答

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