关于ViewHolder的终极优化

传统ViewHolder存在问题举例：

  <pre class="java" name="code">	@Override
		public View getView(final int position, View convertView, ViewGroup parent) {
			ViewHolder viewHolder = null;
			if (convertView == null) {
				viewHolder = new ViewHolder();
				convertView = getLayoutInflater().inflate(R.layout.lv_item_publish_image, null);
				viewHolder.imageView = (ImageView) convertView.findViewById(R.id.imageView);
				viewHolder.rightSignImage = convertView.findViewById(R.id.rightSignImage);
				ViewGroup.LayoutParams lp = viewHolder.imageView.getLayoutParams();
				lp.width = lp.height = imageSize;
				convertView.setTag(viewHolder);
			} else {
				viewHolder = (ViewHolder) convertView.getTag();
			}
			if (position == getDataCount()) {
				ImageLoader.getInstance().cancelDisplayTask(viewHolder.imageView);
				viewHolder.imageView.setImageResource(R.drawable.sl_icon_add_photo);
				viewHolder.rightSignImage.setVisibility(View.GONE);
				viewHolder.rightSignImage.setOnClickListener(null);
			} else {
				String data = getItem(position);

				String uri = null;
				if (data.startsWith("http")) {
					uri = data;
				} else {
					uri = Uri.fromFile(new File(data)).toString();
				}
				ImageLoader.getInstance().displayImage(uri, viewHolder.imageView, option);
				viewHolder.rightSignImage.setVisibility(View.VISIBLE);
				viewHolder.rightSignImage.setOnClickListener(new OnClickListener() {
					@Override
					public void onClick(View v) {
						remove(position);
						notifyDataSetChanged();
					}
				});
			}

			return convertView;
		}

		private static final class ViewHolder {
			ImageView imageView;
			View rightSignImage;
		}
	}

如上。如果你的项目巨大 ，将会有很多Adapter 每个类是不是都要写一个 viewHolder?是不是很操蛋。为何不精简下呢？

Java的重构思想就是要减少重复对不对？如何做？

 

解决办法：单独新建ViewHolder

public class ViewHolder {

	private final SparseArray<View> sparseVies;
	private View convertView;

	private ViewHolder(Context context, int itemResourceId) {
		sparseVies = new SparseArray<View>();
		convertView = LayoutInflater.from(context).inflate(itemResourceId, null);
		convertView.setTag(this);
	}
	
	private ViewHolder(Context context, int itemResourceId,ViewGroup viewGroup) {
		sparseVies = new SparseArray<View>();
		convertView = LayoutInflater.from(context).inflate(itemResourceId, viewGroup);
		convertView.setTag(this);
	}
	

	public static ViewHolder get(Context context, View convertView, int itemResourceId) {
		if (convertView == null) {
			return new ViewHolder(context, itemResourceId);
		}
		return (ViewHolder) convertView.getTag();
	}
	
	public static ViewHolder get(Context context, View convertView, int itemResourceId,ViewGroup  vierGroup) {
		if (convertView == null) {
			return new ViewHolder(context, itemResourceId,vierGroup);
		}
		return (ViewHolder) convertView.getTag();
	}
	

	public <T extends View> T getView(int viewId) {
		View view = sparseVies.get(viewId);
		if (view == null) {
			view = convertView.findViewById(viewId);
			sparseVies.put(viewId, view);
		}
		return (T) view;
	}

	public <T extends View> T findViewById(int viewId) {
		return getView(viewId);
	}

	public View getConvertView() {
		return convertView;
	}

}

 

那么任何Adapter根本不用重新建立 Viewholder 使用办法：

	public View getView(int position, View convertView, ViewGroup parent) {
		ViewHolder mViewHolder = ViewHolder.get(getActivity(), convertView, R.layout.lv_item_message_call);

		//convertView = getLayoutInflater().inflate(R.layout.lv_item_message_call, null);
		ImageView img_avatar = (ImageView) mViewHolder.findViewById(R.id.img_avatar);
		ImageView img_merchant = (ImageView) mViewHolder.findViewById(R.id.img_merchant);
		View ll_call = mViewHolder.findViewById(R.id.ll_call);
		ImageView img_call_type = (ImageView) mViewHolder.findViewById(R.id.img_call_type);
		TextView tv_count = (TextView) mViewHolder.findViewById(R.id.tv_count);
		TextView tv_name = (TextView) mViewHolder.findViewById(R.id.tv_name);
		TextView tv_time = (TextView) mViewHolder.findViewById(R.id.tv_time);
		ll_call.setOnClickListener(this);
		return mViewHolder.getConvertView();
	}

注意点：这个时候连convertview是不是为空都根本不用判断：

直接初始化ViewHolder了。因为提取的ViewHolder已做单独判断。精简完成！over

任何新建的Adapter里完全不必要新建一个ViewHolder所有的Adapter都可以用此ViewHolder.

 

ps:如果感觉此篇文章对你有所帮助。请赞助本人一点闲余资金，买个棒棒糖吃。