Android自定義適配器getView（）空指針異常

Question

我想創建一個網格視圖，它有一個Imageview.I試圖擴展BaseAdapter但我碰到了這個問題，我會很高興，如果有人能指出我正在做的錯誤。

logcat的：

07-10 19:29:00.881: D/AndroidRuntime(1678): Shutting down VM 
07-10 19:29:00.881: W/dalvikvm(1678): threadid=1: thread exiting with uncaught exception (group=0xb3a47b90) 
07-10 19:29:00.901: E/AndroidRuntime(1678): FATAL EXCEPTION: main 
07-10 19:29:00.901: E/AndroidRuntime(1678): Process: com.shrek.try2, PID: 1678 
07-10 19:29:00.901: E/AndroidRuntime(1678): java.lang.NullPointerException 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at com.shaastra.try2.MainActivity$lAdapter.getView(MainActivity.java:80) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.widget.AbsListView.obtainView(AbsListView.java:2263) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.widget.GridView.onMeasure(GridView.java:1044) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.View.measure(View.java:16458) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:719) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:455) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.View.measure(View.java:16458) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.View.measure(View.java:16458) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.View.measure(View.java:16458) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2289) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.View.measure(View.java:16458) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1914) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1111) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1293) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5582) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.Choreographer.doCallbacks(Choreographer.java:562) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.Choreographer.doFrame(Choreographer.java:532) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.os.Handler.handleCallback(Handler.java:733) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.os.Handler.dispatchMessage(Handler.java:95) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.os.Looper.loop(Looper.java:137) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at android.app.ActivityThread.main(ActivityThread.java:4998) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at java.lang.reflect.Method.invokeNative(Native Method) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at java.lang.reflect.Method.invoke(Method.java:515) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593) 
07-10 19:29:00.901: E/AndroidRuntime(1678):  at dalvik.system.NativeStart.main(Native Method) 

其示出了在nullpointexception 線80（mainactivity和customadapter在mainAcitivity.java定義）：

mainActivity.java：

package com.shrek.try2; 

import android.os.Bundle; 
import android.app.Activity; 
import android.content.Context; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.BaseAdapter; 
import android.widget.GridView; 
import android.widget.ImageView; 

public class MainActivity extends Activity{// implements  OnItemClickListener { 

    GridView myGrid; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    myGrid = (GridView) findViewById(R.id.gridView); 
    myGrid.setAdapter(new lAdapter(this)); 
} 

class lAdapter extends BaseAdapter 
{ 
    private final int[] lectimages={R.drawable.image_1,R.drawable.image_2,R.drawable.image_3,R.drawable.image_4,R.drawable.image_5,R.drawable.image_6,R.drawable.image_7,R.drawable.image_8,R.drawable.image_9}; 
    Context c; 
    lAdapter(Context c) 
    { 
     this.c = c; 
    } 
    @Override 
    public int getCount() { 
     // TODO Auto-generated method stub 
     return lectimages.length; 
    } 

    @Override 
    public Object getItem(int arg0) { 
     // TODO Auto-generated method stub 
     return null; 
    } 

    @Override 
    public long getItemId(int arg0) { 
     // TODO Auto-generated method stub 
     return 0; 
    } 


    @Override 
    public View getView(int i, View convertView, ViewGroup parent)  { 
     // TODO Auto-generated method stub 
     View item; 
      LayoutInflater inflater=(LayoutInflater) c.getSystemService(c.LAYOUT_INFLATER_SERVICE); 
      item = inflater.inflate(R.layout.single_item, parent, false); 
      ImageView lect = (ImageView) findViewById(R.id.imageView_1); 
      lect.setImageResource(lectimages[i]); 
     return item; 

    } 

} 
} 

這意味着在getView方法中，行lect爲空，因此findviewb ybyid是返回空，但我已經採取了正確的ID，圖像已被添加到可繪製和詳細的佈局（single_item.xml）已經膨脹：

single_item.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:id="@+id/imageView_1" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:src="@drawable/ic_launcher" 
    android:layout_centerVertical="true" 
    android:layout_centerHorizontal="true" 
    android:contentDescription="imageViewDescription"/> 
</RelativeLayout> 

和activity_main.xml中：

<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:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
tools:context=".MainActivity" > 

<GridView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:id="@+id/gridView" 
    android:layout_alignParentTop="true" 
    android:layout_alignParentLeft="true" 
    android:numColumns="auto_fit" 
    android:horizontalSpacing="0dp" 
    android:verticalSpacing="0dp" 
    android:columnWidth="120dp" 
    android:stretchMode="spacingWidthUniform" 
    /> 

</RelativeLayout> 

請請幫我，我被困在這個問題上約10小時了。

Answer 1

LECT是null，因爲你用findViewById(R.id.imageView_1)，這會在你的ActivityLayout搜索imageView_1並返回null如果沒有找到。

雖然你的ImageView在你的ItemView，你必須找到它在你的itemView使用View.findViewById()像這樣。

item.findViewById(R.id.imageView_1);