java为什么我要在GridView的onMeasure中使用空指针

1 周，3 日 Questions & Answers 3384

当我尝试使用Universal Image Loader在gridview中设置图像时，会出现nullpointer异常。崩溃发生在下载第一个映像时，而在应用程序崩溃之前，正好下载了一个映像。（与httpscoop一起检查）

编辑：这是错误的。崩溃发生在下载第一个图像之前，因此它可能试图测量一个不存在的图像

这是我的行李

<LinearLayout xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
安卓:layout_width="match_parent"
安卓:layout_height="match_parent"
安卓:orientation="vertical" >

<ImageView
    安卓:id="@+id/gridImageView"
    安卓:layout_width="match_parent"
    安卓:layout_height="match_parent" 
    安卓:src="@drawable/ic_launcher"
    安卓:contentDescription="@string/gallery_grid_image_desc"/>

gridview布局只是一个gridview

<GridView xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
    安卓:id="@+id/galleryPicturesGrid"
    安卓:layout_width="match_parent"
    安卓:layout_height="match_parent"
    安卓:orientation="vertical"
    安卓:verticalSpacing="@dimen/gallery_grid_spacing"
    安卓:horizontalSpacing="@dimen/gallery_grid_spacing"
    安卓:numColumns="3" />

我的getView

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View view = convertView;
        ViewHolder holder = null;
        Log.d(TAG, "getView " + position);

        if (view == null) {
            view = ((Activity) context).getLayoutInflater().inflate(
                    R.layout.gallery_grid_item, null);
            holder = new ViewHolder();
            holder.thumb = (ImageView) view.findViewById(R.id.gridImageView);

            view.setTag(holder);
        } else {
            holder = (ViewHolder) view.getTag();
        }

        Picture picture = mPictures.valueAt(position);

        mImageLoader.displayImage(picture.getThumbUrl(), holder.thumb, mImageOptions);

        return null;
    }

ImageLoader配置

    ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(
            getApplicationContext()).memoryCacheSize(2 * 1024 * 1024)
            .discCache(new UnlimitedDiscCache(cacheDir))
            .denyCacheImageMultipleSizesInMemory()
            .offOutOfMemoryHandling()
            .threadPoolSize(4)
            .discCacheFileNameGenerator(new Md5FileNameGenerator())
            .memoryCache(new UsingFreqLimitedMemoryCache(2 * 1024 * 1024))
            .tasksProcessingOrder(QueueProcessingType.LIFO)
            .imageDownloader(new UrlConnectionImageDownloader(this))
            .build();

和选择

    galleryThumbImageOptions = new DisplayImageOptions.Builder()
    .showStubImage(R.drawable.p1_cover)
    .cacheOnDisc()
    .bitmapConfig(Bitmap.Config.RGB_565)
    .build();

例外呢

01-18 10:56:15.434: E/AndroidRuntime(4089): FATAL EXCEPTION: main   
01-18 10:56:15.434: E/AndroidRuntime(4089): java.lang.NullPointerException
01-18 10:56:15.434: E/AndroidRuntime(4089):     at     安卓.widget.GridView.onMeasure(GridView.java:937)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.View.measure(View.java:8313)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.View.measure(View.java:8313)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.View.measure(View.java:8313)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.widget.LinearLayout.measureVertical(LinearLayout.java:386)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.widget.LinearLayout.onMeasure(LinearLayout.java:309)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.View.measure(View.java:8313)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.View.measure(View.java:8313)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.widget.LinearLayout.measureVertical(LinearLayout.java:531)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.widget.LinearLayout.onMeasure(LinearLayout.java:309)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.View.measure(View.java:8313)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.View.measure(View.java:8313)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.View.measure(View.java:8313)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.ViewRoot.performTraversals(ViewRoot.java:839)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.view.ViewRoot.handleMessage(ViewRoot.java:1859)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.os.Handler.dispatchMessage(Handler.java:99)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.os.Looper.loop(Looper.java:123)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at 安卓.app.ActivityThread.main(ActivityThread.java:3683)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at java.lang.reflect.Method.invokeNative(Native Method)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at java.lang.reflect.Method.invoke(Method.java:507)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:597)
01-18 10:56:15.434: E/AndroidRuntime(4089):     at dalvik.system.NativeStart.main(Native Method)

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java为什么我要在GridView的onMeasure中使用空指针

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