传统的ListView写法
传统的ListView方法是每个ListView都要一个Adapter，这个Adapter继承BaseAdapter，重写四个方法。在getView()方法中获取各种View然后set。高级一点的写法就是使用ViewHolder缓存已经加载的View，然后再获取。这种写法对于ListView数目较少时比较合适，对于实际项目来说并不合适。
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| ViewHolder viewHolder;
View view;
if (convertView == null) {
view = mInflater.inflate(R.layout.item, null);
viewHolder = new ViewHolder();
viewHolder.tv_title = (TextView) view.findViewById(R.id.tv_title);
viewHolder.tv_content = (TextView) view.findViewById(R.id.tv_content);
viewHolder.tv_time = (TextView) view.findViewById(R.id.tv_time);
viewHolder.tv_phone = (TextView) view.findViewById(R.id.tv_phone);
view.setTag(viewHolder);
} else {
view=convertView;
viewHolder = (ViewHolder) view.getTag();
}
Bean bean = getItem(position);
viewHolder.tv_title.setText(bean.getTitle());
viewHolder.tv_content.setText(bean.getDescribe());
viewHolder.tv_time.setText(bean.getTime());
viewHolder.tv_phone.setText(bean.getPhone());
return view;
}
private class ViewHolder {
TextView tv_title;
TextView tv_content;
TextView tv_time;
TextView tv_phone;
}
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Adapter优化
ViewHolder的封装
在通常的写法中，用成员变量来保存View，而在这里采用SparseArray来保存View（SparseArray是android里为这样的Hashmap而专门写的class,目的是提高效率）。代码如下
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| private SparseArray<View> mViews;
private int position;
private View mConvertView;
public ViewHolder(Context context, ViewGroup parent, int layoutId, int position) {
this.position = position;
this.mViews = new SparseArray<>();
mConvertView = LayoutInflater.from(context).inflate(layoutId, parent, false);
mConvertView.setTag(this);
}
*提供入口方法
*/
public static ViewHolder get(Context context, View convertView,
ViewGroup parent, int position, int layoutId) {
if (convertView == null) {
return new ViewHolder(context, parent, layoutId, position);
} else {
ViewHolder holder = (ViewHolder) convertView.getTag();
holder.position = position;
return holder;
}
}
* 通过viewId获取控件
*返回一个View的子类
* @return
*/
public <T extends View> T getView(int viewId) {
View view = mViews.get(viewId);
if (view == null) {
view = mConvertView.findViewById(viewId);
mViews.put(viewId, view);
}
return (T) view;
}
public View getConvertView() {
return mConvertView;
}
public ViewHolder setText(int viewId, String text) {
TextView tv = getView(viewId);
tv.setText(text);
return this;
}
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Adapter的封装
创建抽象类CommonAdapter，使其继承BaseAdapter，重写四个方法。在重写getView()方法的时候，就可以使用ViewHolder.get()这个入口方法了。最后创建抽象方法convert(),参数分别为ViewHolder和T，第一个参数旨在让用户取得ViewHolder对象来调用其方法；第二个参数为泛型T，指定Java Bean的类型。代码如下：
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| public abstract class CommonAdapter<T> extends BaseAdapter {
protected List<T> mList;
protected Context mContext;
protected LayoutInflater mInflater;
public CommonAdapter(Context context, List<T> mList) {
this.mList = mList;
this.mContext = context;
mInflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return mList.size();
}
@Override
public T getItem(int position) {
return mList.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = ViewHolder.get(mContext, convertView, parent, position, R.layout.item);
convert(holder, getItem(position));
return holder.getConvertView();
}
public abstract void convert(ViewHolder holder, T t);
}
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以上通过对ViewHolder和Adapter的封装，是的我们在使用ListView的时候变得十分简单：直接继承CommonAdapter重写convert()方法即可。甚至为了简便，可以直接在setAdapter的时候新建内部类，省去了继承CommonAdapter的过程。以后再使用的时候直接复制这些代码即可。
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| mListView.setAdapter(new CommonAdapter<Bean>(MainActivity.this, mList) {
@Override
public void convert(ViewHolder holder, Bean bean) {
holder.setText(R.id.tv_title, bean.getTitle())
.setText(R.id.tv_content, bean.getDescribe())
.setText(R.id.tv_time, bean.getTime())
.setText(R.id.tv_phone, bean.getPhone());
}
});
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