findViewById（）方法有時只返回null（大多數時間工作正常）

我在這裏遇到一個很奇怪的問題。在我的fragment中，經過我的inflatelayout,findViewById()方法有時會返回null。但這個問題根本不可重現。我收到Crashlytics的這些崩潰報告。而且這次事故也發生在QA的其中一位成員身上，但之後他也無法再現這個問題。findViewById（）方法有時只返回null（大多數時間工作正常）

這裏是我的片段代碼

 @Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
    View customView= inflater.inflate(R.layout.custom_view, container, false); 
    ImageView back= (ImageView) customView.findViewById(R.id.back); 

    //Throwing Null Pointer Exception for the below line. 
    back.someFunc(); 
    return customView; 
}

XML文件：

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
       xmlns:app="http://schemas.android.com/apk/res-auto" 
       android:id="@+id/topics_parent" 
       android:layout_width="match_parent" 
       android:layout_height="match_parent" 
       android:orientation="vertical" 
       android:background="?attr/default_background"> 

    <ImageView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_alignParentBottom="true" 
     android:layout_alignParentRight="true" 
     android:layout_marginRight="@dimen/back_to_top_margin_right" 
     android:layout_marginBottom="@dimen/back_to_top_margin_bottom" 
     android:src="@drawable/back" 
     android:visibility="gone" 
     android:id="@+id/back"/> 

    <LinearLayout 
     android:id="@+id/error_parent" 
     android:layout_width="match_parent" 
     android:background="?attr/default_background" 
     android:orientation="vertical" 
     android:layout_height="match_parent"> 
    </LinearLayout> 

    <ProgressBar 
     android:id="@+id/progressbar" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_centerInParent="true"/> 
</RelativeLayout>

崩潰日誌

Fatal Exception: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp/com.myapp.news.activities.NewsHomeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2316) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2376) 
     at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3928) 
     at android.app.ActivityThread.access$900(ActivityThread.java:147) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1287) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:135) 
     at android.app.ActivityThread.main(ActivityThread.java:5253) 
     at java.lang.reflect.Method.invoke(Method.java) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 
Caused by java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference 
     at com.myapp.news.fragments.TopicsGroupFragment.onCreateView(TopicsGroupFragment.java:157) 
     at android.app.Fragment.performCreateView(Fragment.java:2053) 
     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:894) 
     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067) 
     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1049) 
     at android.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1869) 
     at android.app.Activity.performCreateCommon(Activity.java:5970) 
     at android.app.Activity.performCreate(Activity.java:5977) 
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2269) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2376) 
     at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3928) 
     at android.app.ActivityThread.access$900(ActivityThread.java:147) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1287) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:135) 
     at android.app.ActivityThread.main(ActivityThread.java:5253) 
     at java.lang.reflect.Method.invoke(Method.java) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

有一個很艱難的時間弄清楚爲什麼findViewById()將返回空值那種觀點。

注：我有很多ImageViewresources其ID是back但他們都在不同的XML文件。

來源

2016-06-13 thedarkpassenger

'查看customView = inflater.inflate（R.layout.custom_view，容器，FALSE）; ImageView back =（ImageView）topicsView.findViewById（R.id.back）;'?? 不應該是'（ImageView）customView.findViewById（R.id.back）;'?? – SripadRaj

'topicsView'在哪裏？如果從'onCreateView'方法返回'customView'方法，它應該是'customView'來訪問佈局視圖 –

爲什麼當你在'customView'中膨脹佈局時使用'topicsView'？ –

您增加觀看到customView當您使用topicsView找到其ID ....

變化topicsView到customView

ImageView back= (ImageView) customView.findViewById(R.id.back);

來源

2016-06-13 05:22:14 nitinkumarp

這是一個類型錯誤。我在其中一個地方修改了變量名，並忘記在其他地方更改發佈問題。我修改了這個問題。 – thedarkpassenger

指定自定義視圖findviewbyId。因爲您在customView內將Layout充氣。

View customView= inflater.inflate(R.layout.custom_view, container, false); 
ImageView back= (ImageView) customView.findViewById(R.id.back);

更改您的Multiple image resources ID來唯一所有。

對於e.g back，back1，back2等。

來源

2016-06-13 05:22:34

這是一個類型錯誤。我在其中一個地方修改了變量名，並忘記在其他地方更改發佈問題。我修改了這個問題。 – thedarkpassenger

@thedarkpassenger發佈您的完整崩潰日誌。而'customview.xml'也是代碼。 –

可能是因爲您太早調用它。

等到onFinishInflate（）。這是一個示例項目，演示訪問其內容的自定義視圖。

https://github.com/commonsguy/cw-omnibus/tree/master/Jank/ThreePaneBC

來源

2016-06-13 05:24:16 AxeManTOBO

當你正在膨脹名爲customView變量視圖，並且您使用topicsView視圖ImageView的，這是不對的。

下面是完整的代碼

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
    View customView= inflater.inflate(R.layout.custom_view, container, false); 
    ImageView back= (ImageView) customView.findViewById(R.id.back); 


    back.someFunc(); 
    return customView; 
}

來源

2016-06-13 05:26:34

爲了避免碰撞使空校驗

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
View customView= inflater.inflate(R.layout.custom_view, container, false); 
ImageView back= (ImageView) customView.findViewById(R.id.back); 

if(back!=null) 
back.someFunc(); 
}

來源

2016-06-13 05:27:28

It may be because in OnCreateView THE VIEW is not fully created try to use following code: 

    /*---------- WHEN THIS FRAGMENT VIEW IS CREATING --------------------------*/ 
    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
     return inflater.inflate(getLayoutId(), container, false); 
    } 

    /*---------- WHEN FRAGMENT VIEW IS CREATED --------------------------*/ 
    @Override 
    public void onViewCreated(View view, Bundle savedInstanceState) { 
     super.onViewCreated(view, savedInstanceState); 
     ImageView back= (ImageView) view.findViewById(R.id.back); 
     back.someFunc(); 
    }

來源

2016-06-13 05:44:34

我會盡力實現它。謝謝。 – thedarkpassenger

使用OnCreateView佈局設置爲您的片段，並使用onActivityCreated創建對象到您的像下面的代碼的意見。

public class test extends Fragment 
{ 
    View view; 

    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) 
    { 
     return view = inflater.inflate(R.layout.fragment_page, container, false); 
    } 

    @Override 
    public void onActivityCreated(@Nullable Bundle savedInstanceState) 
    { 
     super.onActivityCreated(savedInstanceState); 

     ImageView back= (ImageView) view.findViewById(R.id.back); 
    } 
}

來源

2016-06-13 06:15:08

會人爲增加在名爲customView變量視圖而你正在使用ImageView的，這就是爲什麼你得到空指針異常topicsView視圖。

Lets See the full code.  


    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    View customView= inflater.inflate(R.layout.custom_view, container, false); 
    ImageView back= (ImageView) customView.findViewById(R.id.back); 

    back.someFunc(); 
    return customView;

}

來源

2016-06-13 07:23:52 Ramesh

findViewById（）方法有時只返回null（大多數時間工作正常）

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