ListView为什么要使用convertView和ViewHolder

原因就是：

1. 使用convertView可以避免重复地调用inflate

2. 使用ViewHolder可以避免重复地调用findViewById

下面的getView代码来自于

[plain] view plain copy

[java] view plain copy

/**
*Makeaviewtoholdeachrow.
*
*@seeandroid.widget.ListAdapter#getView(int,android.view.View,
*android.view.ViewGroup)
*/
publicViewgetView(intposition,ViewconvertView,ViewGroupparent){
//AViewHolderkeepsreferencestochildrenviewsto<spanstyle="color:#ff0000;">avoidunneccessarycalls
//tofindViewById()</span>oneachrow.
ViewHolderholder;
//WhenconvertViewisnotnull,wecanreuseitdirectly,<spanstyle="color:#ff0000;">thereisnoneed
//toreinflateit.</span>WeonlyinflateanewViewwhentheconvertViewsupplied
//byListViewisnull.
if(convertView==null){
convertView=mInflater.inflate(R.layout.list_item_icon_text,null);
//CreatesaViewHolderandstorereferencestothetwochildrenviews
//wewanttobinddatato.
holder=newViewHolder();
holder.text=(TextView)convertView.findViewById(R.id.text);
holder.icon=(ImageView)convertView.findViewById(R.id.icon);
convertView.setTag(holder);
}else{
//GettheViewHolderbacktogetfastaccesstotheTextView
//andtheImageView.
holder=(ViewHolder)convertView.getTag();
}
//Bindthedataefficientlywiththeholder.
holder.text.setText(DATA[position]);
holder.icon.setImageBitmap((position&1)==1?mIcon1:mIcon2);
returnconvertView;
}

更多相关文章