android自定义BaseAdapter，实现从网络加载包含图片的listview

最新推荐文章于 2022-04-02 09:59:43 发布

qiu_xiaojie

最新推荐文章于 2022-04-02 09:59:43 发布

阅读量3.2k

点赞数

CC 4.0 BY-SA版权

分类专栏： android 文章标签： listview 自定义listview

本文链接：https://blog.youkuaiyun.com/u010558325/article/details/39716983

android 专栏收录该内容

3 篇文章

订阅专栏

本文介绍如何在Android中创建一个自定义BaseAdapter，以实现从网络加载并显示包含图片的ListView。通过使用ViewHolder优化，有效减少内存消耗。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

public class NetImgAdapter extends BaseAdapter{
	
	private Context context;
	private List<HashMap<String, String>> dataList;
	private int itemId;
	private String[] fromArr;
	private int[] toArr;
	//bitmap哈希
	private HashMap<String, Bitmap> bitmapHashMap = new HashMap<String, Bitmap>();
	private Bitmap bitmap;
	//异步处理类
	private MyHendler myHendler = new MyHendler();
	
	/**
	 * 
	 * @param context 上下文对象
	 * @param dataList listview数据
	 * @param itemId item layout布局id
	 * @param fromArr 需要显示的数据
	 * @param toArr 数据的布局id
	 */
	public NetImgAdapter(Context context, List<HashMap<String, String>> dataList, int itemId, String[] fromArr, int[] toArr) {
		this.context = context;
		this.dataList = dataList;
		this.itemId = itemId;
		this.fromArr = fromArr;
		this.toArr = toArr;
	}
	

	@Override
	public int getCount() {
		// TODO Auto-generated method stub
		return dataList.size();
	}

	@Override
	public Object getItem(int position) {
		// TODO Auto-generated method stub
		return dataList.get(position);
	}

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

	@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		 if (convertView == null) {
		        convertView = LayoutInflater.from(context)
		          .inflate(itemId, parent, false);
		    }
		 for (int i = 0; i < toArr.length; i++) {
			View v = ViewHolder.get(convertView, toArr[i]);
			if (v instanceof TextView) {
				//view是textview
				TextView tv = (TextView) v;
				String content = dataList.get(position).get(fromArr[i]);
				tv.setText(content);
			}
			if (v instanceof ImageView) {
				ImageView iv = (ImageView) v;
				final String content = dataList.get(position).get(fromArr[i]);
				bitmap = bitmapHashMap.get(content);
				if (bitmap != null) {
					//已经加载了图片，直接显示
					iv.setImageBitmap(bitmap);
				} else {
					new Thread() {

						@Override
						public void run() {
							//没有加载图片，从网络加载
							bitmap = HttpHelper.getBitMap(content);
							//bitmapArray.put(toArr[i], bitmap);
							bitmapHashMap.put(content, bitmap);
							myHendler.sendEmptyMessage(0);
							super.run();
						}
						
					}.start();
				}
			}
		}
		 return convertView;
	}
	
	private class MyHendler extends Handler {

		@Override
		public void handleMessage(Message msg) {
			switch (msg.what) {
			case 0:
				notifyDataSetChanged();
				break;

			default:
				break;
			}
			super.handleMessage(msg);
		}
		
	}

}

调用与simpleadapter一样，图片用url传入，可以直接从网络加载带图片的列表

通用viewholder，减少内存

public class ViewHolder {
	
	// I added a generic return type to reduce the casting noise in client code
    @SuppressWarnings("unchecked")
	public static <T extends View> T get(View view, int id) {
        SparseArray<View> viewHolder = (SparseArray<View>) view.getTag();
        if (viewHolder == null) {
            viewHolder = new SparseArray<View>();
            view.setTag(viewHolder);
        }
        View childView = viewHolder.get(id);
        if (childView == null) {
            childView = view.findViewById(id);
            viewHolder.put(id, childView);
        }
        return (T) childView;
    }
    
}