Adapter基础（未完）

Adapter的作用，顾名思义，作为适配器，在Android中向调用者（如List等）提供整合了数据的View对象。

其主要方法是getView()。该方法返回View对象给需要的调用者（比如List）。怀疑该方法在List布局的时候被调用（还未找到源码)。比如List布局时发现一屏需要插入10个View，就调用Adapter.getView()共10次。

注意：getView()的第二个参数View很重要，如果由List提供了View过来，则无需再创建新的View，直接使用就好。

 

View的回收？？

 

如何高效使用Adapter？以下转自How you create your view for listview on Android?

How you create your view for listview on Android?
There have three versions of getView() function,
the first version is a slow way,and the last is the fastest one.

Version 1:

public View getView(int position, View convertView, ViewGroup parent) {
     View item = mInflater.inflate(R.layout.list_item_icon_text, null);
      ((TextView) item.findViewById(R.id.text)).setText(DATA[position]);
      ((ImageView) item.findViewById(R.id.icon)).setImageBitmap(
     (position & 1) == 1 ? mIcon1 : mIcon2);
      return item;
 }

 

Version 2:

public View getView(int position, View convertView, ViewGroup parent) {
    if (convertView == null) {
      convertView = mInflater.inflate(R.layout.item, parent, false);
    }
    ((TextView) convertView.findViewById(R.id.text)).setText(DATA[position]);
     ((ImageView) convertView.findViewById(R.id.icon)).setImageBitmap(
     (position & 1) == 1 ? mIcon1 : mIcon2);
     return convertView;
 }

Version 3: the fast way for getView function.

static class ViewHolder {
  TextView text;
  ImageView icon;
}

public View getView(int position, View convertView, ViewGroup parent) {
   ViewHolder holder;

  if (convertView == null) {
     convertView = mInflater.inflate(R.layout.list_item_icon_text,parent, false);
     holder = new ViewHolder();
     holder.text = (TextView) convertView.findViewById(R.id.text);
     holder.icon = (ImageView) convertView.findViewById(R.id.icon);
     convertView.setTag(holder);
   } else {
     holder = (ViewHolder) convertView.getTag();
   }

   holder.text.setText(DATA[position]);
   holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);
   return convertView;

}

 

The last version use setTag() and getTag() to get a more high performance,
if you use the first or second version of getView(), it is the time to refactoring your code to the third version.

 

参考：

1. Android Adapter 接口中几个方法的研究

2. Android-Adapter应用总结 — Windows Live

3. How you create your view for listview on Android?