ListView的另一种可读性更强的ViewHolder模式写法

常见的写法是这样的：

@Override
            public View getView(int position, View convertView, ViewGroup parent) {
                ViewHolder viewHolder;
                
                if( convertView == null ) {
                    convertView = getLayoutInflater().inflate( R.layout.line, null );
                    ImageView imageView = (ImageView) convertView.findViewById( R.id.imageView );
                    TextView textView = (TextView) convertView.findViewById( R.id.textView );
                    viewHolder = new ViewHolder();
                    viewHolder.imageView = imageView;
                    viewHolder.textView = textView;
                    convertView.setTag( viewHolder );
                } else {
                    viewHolder = (ViewHolder) convertView.getTag();
                }

                viewHolder.imageView.setImageResource( R.drawable.ic_launcher );
                viewHolder.textView.setText( arr[ position ] + "");
                return convertView;
            }

但是可读性不好，convertView怎么会当成getView的返回值呢？所以以下是一种更好的写法：

@Override
            public View getView(int position, View convertView, ViewGroup parent) {
                ViewHolder viewHolder;
                if( convertView == null ) {
                    View view = getLayoutInflater().inflate( R.layout.line, null );
                    ImageView imageView = (ImageView) view.findViewById( R.id.imageView );
                    TextView textView = (TextView) view.findViewById( R.id.textView );
                    viewHolder = new ViewHolder();
                    viewHolder.imageView = imageView;
                    viewHolder.textView = textView;
                    view.setTag( viewHolder );
                    viewHolder.imageView.setImageResource( R.drawable.ic_launcher );
                    viewHolder.textView.setText( arr[ position ] + "");
                    return view;
                } else {
                    viewHolder = (ViewHolder) convertView.getTag();
                    viewHolder.imageView.setImageResource( R.drawable.ic_launcher );
                    viewHolder.textView.setText( arr[ position ] + "");
                    return convertView;
                }
            }

 

因为convertView只是指向一块内存区域，它保存着已显示过的View。只有ListView没超出屏幕时，convertView才为空。如果超出了，convertView就有东西了。

附：ViewHolder如下：

class ViewHolder {
        TextView textView;
        ImageView imageView;
    }