java – GridView scrollBar：动态添加图像时的不稳定行为

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:orientation="vertical"
          android:layout_width="match_parent"
          android:layout_height="match_parent">

    <!-- This is basically a HorizontalScrollView where i add some buttons -->
    <com.my.HorizontalButtonScrollList
        android:id="@+id/horizontalButtonScrollList"
        android:layout_width="match_parent"
        android:layout_height="50dip">
    </com.my.HorizontalButtonScrollList>

    <android.support.v4.widget.SwipeRefreshLayout
        android:id="@+id/swipeRefreshLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <GridView
            android:id="@+id/gridView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:columnWidth="100dp"
            android:numColumns="2"
            android:verticalSpacing="0dp"
            android:horizontalSpacing="0dp"
            android:stretchMode="columnWidth"
            android:gravity="center"
            android:scrollbars="vertical">
        </GridView>

    </android.support.v4.widget.SwipeRefreshLayout>

</LinearLayout>

public class PhotoGalleryActivity extends myBaseView {

    private GridView gridView;
    private PhotoGalleryImageAdapter imageAdapter;
    private PhotoGalleryModel[] photoGalleryModels;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.photo_gallery);
        gridView = (GridView) findViewById(R.id.gridView);

        loadImages();
    }

    void loadImages() {

        photoGalleryModels = PhotoGalleryModel.getFakeData();
        imageAdapter = new PhotoGalleryImageAdapter(this,photoGalleryModels);
        gridView.setAdapter(imageAdapter);
    }
}

public class PhotoGalleryImageAdapter extends BaseAdapter {

    private Context mContext;
    private PhotoGalleryModel[] photoGalleryModels;

    public PhotoGalleryImageAdapter(Context c,PhotoGalleryModel[] models){
        mContext = c;
        photoGalleryModels = models;
    }

    @Override
    public int getCount() { return photoGalleryModels.length; }

    @Override
    public Object getItem(int position) { return null; }

    @Override
    public long getItemId(int position) { return 0; }

    @Override
    public View getView(int position,View convertView,ViewGroup parent) {

        final ImageView imageView = new ImageView(mContext);    
        DownloadImageWithURL(photoGalleryModels[position].thumb_image_url,new MyHttpCallback() {
            @Override
            public void MyHttpCallback_OnSuccess(Object data,String responseString)
            {
                if(data instanceof Bitmap) {
                    imageView.setImageBitmap((Bitmap)data);
                }
            }

            @Override
            public void MyHttpCallback_OnError(String responseString,ErrorDataModel error)
            {}
        });

        convertView = imageView;    
        return convertView;
    }
}

好吧,似乎我通过忽略它来解决问题.在我跳过修复gridView之后,因为我不知道该怎么做,我实现了使用LruCache缓存图像(如Android开发人员的 training page所示)以节省一些内存.突然,gridView的滚动行为也得到了修复.

以下是我的更改：

PhotoGalleryImageAdapter(现在有缓存)

public class PhotoGalleryImageAdapter extends BaseAdapter {

    private Context mContext;
    private PhotoGalleryModel[] photoGalleryModels;
    private LruCache<String,Bitmap> mMemoryCache;

    public PhotoGalleryImageAdapter(Context c,PhotoGalleryModel[] models){
        mContext = c;
        photoGalleryModels = models;

        final int maxMemory = (int)(Runtime.getRuntime().maxMemory() / 1024);
        final int cacheSize = maxMemory / 8;

        mMemoryCache = new LruCache<String,Bitmap>(cacheSize) {
            @Override
        protected int sizeOf(String key,Bitmap bitmap) {
                return bitmap.getByteCount() / 1024;
            }
        };
    }

    @Override
    public int getCount() { return photoGalleryModels.length; }

    @Override
    public Object getItem(int position) { return null; }

    @Override
    public long getItemId(int position) { return 0; }

    @Override
    public View getView(int position,ViewGroup parent) {

        final ImageView imageView = new ImageView(mContext);
        final String imageKey = photoGalleryModels[position].thumb_image_url;
        final Bitmap bitmapImage = mMemoryCache.get(imageKey);

        if (bitmapImage != null) {
            imageView.setImageBitmap(bitmapImage);
        }
        else {

            DownloadImageWithURL(photoGalleryModels[position].thumb_image_url,new MyHttpCallback() {
                @Override
                public void MyHttpCallback_OnSuccess(Object data,String responseString) {
                    if (data instanceof Bitmap) {
                        mMemoryCache.put(imageKey,(Bitmap)data);
                        imageView.setImageBitmap((Bitmap)data);
                    }
                }

                @Override
                public void MyHttpCallback_OnError(String responseString,ErrorDataModel error)
                {}
            });
        }

        convertView = imageView;
        return convertView;
    }

}

我很高兴gridView终于正常工作,但我不满意这样的事实,即如果没有缓存图像,它对我不起作用.我应该在加载图像之前在imageAdapter的getView()方法中设置imageView的边界.我将尝试修复gridView而不使用缓存并更新我的答案,如果我找到了解决方案,以防有人必须面对同样的问题.在那之前,我很高兴我设法让它工作:)

更新：

我终于使用和不使用缓存工作.这是我更新的PhotoGalleryImageAdapter：

public View getView(int position,ViewGroup parent) {

    final ImageView imageView;
       // set the imagge's bounds if it is not loaded yet
    if (convertView == null) {
        imageView = new ImageView(mContext);
        imageView.setLayoutParams(new ViewGroup.LayoutParams(imageSize,imageSize));
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
        imageView.setPadding(0,0);
    }
    else {
        imageView = (ImageView) convertView;
    }

    final String imageKey = photoGalleryModels[position].thumb_image_url;
    final Bitmap bitmapImage = mMemoryCache.get(imageKey);

    if (bitmapImage != null) {
        imageView.setImageBitmap(bitmapImage);
    }
    else {
        imageView.setImageBitmap(emptyBitmap);
        DownloadImageWithURL(photoGalleryModels[position].thumb_image_url,String responseString) {
                    if (data instanceof Bitmap) {
                    mMemoryCache.put(imageKey,(Bitmap)data);
                    imageView.setImageBitmap((Bitmap)data);
                }
            }

            @Override
            public void MyHttpCallback_OnError(String responseString,ErrorDataModel error)
            {}
        });
    }
    convertView = imageView;
    return convertView;
}

正如所料,我需要在加载之前设置图像边界.

因为我将gridView的numColumns参数更改为’auto_fit’,所以图像的宽度/高度(100dp stretchMode columnWidth)计算如下：

int imagesPerRow = screenSize.x / (int)(100 * mContext.getResources().getDisplayMetrics().density);
imageSize = screenSize.x / imagesPerRow;

在加载imageView的bitmapImage之前,我创建一个空的位图图像并将其分配给imageView(找到代码here)：

emptyBitmap = Bitmap.createBitmap(imageSize,imageSize,Bitmap.Config.ARGB_8888);

无论是否使用LruCache,gridView现在都可以正常工作.我不知道对一个人自己的问题是否是常见做法,但在这样做时我认为它可以帮助那些面临类似问题的人.