Listview 对ViewHolder的复用

最新推荐文章于 2021-06-03 01:55:34 发布

原创最新推荐文章于 2021-06-03 01:55:34 发布 · 968 阅读

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本文介绍了一种改进ListView开发效率的方法，通过自定义ViewHolder类使用SparseArray缓存视图，简化了convertView复用过程中的findViewById操作，提升了开发效率。

以前使用Listview 实现convertView的复用, 都是在Adapter中写一个静态类:

其实有时候感觉很不方便

这几天看一个开源项目, 发现使用有个大神写了一个ViewHolder.java的东西,让人耳目一新, 其实是通过一个SparseArray来缓存这些view, 省去了自己

写一堆view将来改造也麻烦的问题效率虽然差了一点点, 但是开发效率提高了不少

public class ViewHolder
{
	final View mRoot;
    //缓存item中各个view , 省去下次findviewbyid 
    final SparseArray<View> mViews = new SparseArray<View>();
	
	public ViewHolder(View root)
	{
		this.mRoot = root;
	}
	
    @SuppressWarnings ("unchecked")
	public <T extends View> T getViewById(int id)
	{
		T view = (T) mViews.get(id);
		if (view == null)
		{
			mViews.put(id, (view = (T) mRoot.findViewById(id)));
			if (view == null)
				throw new NullPointerException("Cannot find requested view id "+String.valueOf(id));
		}
		return view;
	}
	
	public boolean hasView(int id)
	{
		if (mViews.get(id) != null) return true;
		else
		{
			View view = this.mRoot.findViewById(id);
			if (view == null) return false;
			else
			{
				mViews.put(id, view);
				return true;
			}
		}
	}
}

测试代码:

public class MainActivity extends Activity
{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ListView listView = new ListView(this);
        listView.setAdapter(new MyAdapter());
        setContentView(listView);
        
    }
    
    private class MyAdapter extends BaseAdapter
    {
        
        @Override
        public int getCount() {
            return 1000;
        }
        
        @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) {
            if (convertView == null) {
                convertView = buildView(R.layout.layout_item, parent);
            }
            ViewHolder viewHolder = (ViewHolder) convertView.getTag();
            TextView textView = viewHolder.getViewById(R.id.textView1);
            textView.setText("Test" + position);
            return convertView;
        }
        
        //把组装xml view的 函数抽取出来
        protected View buildView(int redId, ViewGroup parent) {
            View view = LayoutInflater.from(MainActivity.this).inflate(redId, parent, false);
            view.setTag(new ViewHolder(view));
            return view;
        }
    }
    
}