Listview显示错误的图像

Question

我有一个带有ArrayAdapter的ListView,它包含一个带有Image和String的行.这工作正常,直到我决定图像的加载速度慢,所以我无法在显示列表之前加载图像.所以我开始使用一个单独的线程加载图像AsyncTask.

在我开始滚动列表之前,我对结果非常满意.加载了错误的图像,看起来这不是一段时间后图像的问题.如果我尝试对列表进行排序,则问题非常严重,并且没有任何图像位于右侧.

我做错了什么想法？

public View getView(int position, View convertView, ViewGroup parent) {
        View v = convertView;
        ImageView imageView;
        TextView textView;
        if (v == null) {
            LayoutInflater vi = (LayoutInflater) getContext().getSystemService(
                    Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.drink_list_row, null);
        }

        Drink drink = allItems.get(position);
        if (drink != null && v != null) {
            imageView = (ImageView) v.findViewById(R.id.picture);
            textView = (TextView) v.findViewById(R.id.drinkName);
            imageView.setVisibility(View.GONE);
            loadImageBitmap(drink, imageView);
            textView.setText(drink.getName());

            if (subItems != null && subItems.contains(drink)) {
                textView.setVisibility(View.VISIBLE);
                imageView.setVisibility(View.VISIBLE);
            } else {
                textView.setVisibility(View.GONE);
                imageView.setVisibility(View.GONE);
            }
        }
        return v;
    }

Answer 1

问题来自你的convertView:它是整个列表中使用的相同的单个实例,因此当你的异步加载完成时,当listview试图使用相同的convertView绘制不同的项时(或者在这种情况下),图像会被更改,它的孩子imageView).

painting position 1, uses placeholder, starts loading image 1 asynchronously
painting position 2, uses placeholder, starts loading image 2 asynchronously
image 1 loading is complete, calling setImageBitmap on imageView
painting position 3, uses image 1, starts loading image 3 asynchronously
etc.

你可以做的是在listadapter中保留Bitmaps的缓存.像这样的东西:

private Bitmap[] bitmapList;
private Bitmap bitmapPlaceholder;  

private void initBitmapListWithPlaceholders(){ 
// call this whenever the list size changes
// you can also use a list or a map or whatever so you 
// don't need to drop all the previously loaded bitmap whenever 
// the list contents are modified
    int count = getListCount();
    bitmapList = new Bitmap[count];
    for(int i=0;i<count;i++){
         bitmapList[i]=bitmapPlaceholder
    }
}

private void onBitmapLoaded(int position, Bitmap bmp){
// this is your callback when the load async is done
    bitmapList[position] = bmp;
}

public View getView(int position, View convertView, ViewGroup parent) {
    View v = convertView;
    ImageView imageView;
    TextView textView;
    if (v == null) {
        LayoutInflater vi = (LayoutInflater) getContext().getSystemService(
                Context.LAYOUT_INFLATER_SERVICE);
        v = vi.inflate(R.layout.drink_list_row, null);
    }

    Drink drink = allItems.get(position);
    if (drink != null && v != null) {
        imageView = (ImageView) v.findViewById(R.id.picture);
        textView = (TextView) v.findViewById(R.id.drinkName);
        imageView.setVisibility(View.GONE);
        imageView.setImageBitmap(bitmapList[position]);
        loadImageBitmap(drink, position); // this should call onBitmapLoaded(int position, Bitmap bmp) when finished to update the bitmapList and replace the placeholder
        textView.setText(drink.getName());

        if (subItems != null && subItems.contains(drink)) {
            textView.setVisibility(View.VISIBLE);
            imageView.setVisibility(View.VISIBLE);
        } else {
            textView.setVisibility(View.GONE);
            imageView.setVisibility(View.GONE);
        }
    }
    return v;
}