ListView中有不同的ViewType，它的convertView实现

a_long_总结：

只要在继承BaseAdapter的MyAdapter中完成以下3点：

1：重写getViewTypeCount()-总共的Type数量；

2：重写getItemViewType(int)-由position来得知Type的id；

3：根据Type在getView中正确的创建convertView；

那么Adapter会调用getTimeViewType方法来判断这个View的类型，从而当View被Recycler回收后，Adapter会自动根据View的Type而正确的返回是否有convertView或者是convertView==null。

这样就实现了一个ListView中有不同的ViewType，而每一个View都被正确的convert（VIewHolder）了，优化性能。

示例代码如下：

参考自：

英文原文：http://android.amberfog.com/?p=296

Different list items’ layouts

Let’s move to the “more complicated” example. How about to add separator somewhere to the list.

You should do the following:

1. Override getViewTypeCount() – return how many different view layouts you have
2. Override getItemViewType(int) – return correct view type id by position
3. Create correct convertView (depending on view item type) in getView

Simple, isn’t it? Code snippet:

public class MultipleItemsList extends ListActivity {     private MyCustomAdapter mAdapter;     @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        mAdapter = new MyCustomAdapter();        for (int i = 1; i < 50; i++) {            mAdapter.addItem("item " + i);            if (i % 4 == 0) {                mAdapter.addSeparatorItem("separator " + i);            }        }        setListAdapter(mAdapter);    }     private class MyCustomAdapter extends BaseAdapter {         private static final int TYPE_ITEM = 0;        private static final int TYPE_SEPARATOR = 1;        private static final int TYPE_MAX_COUNT = TYPE_SEPARATOR + 1;         private ArrayList mData = new ArrayList();        private LayoutInflater mInflater;         private TreeSet mSeparatorsSet = new TreeSet();         public MyCustomAdapter() {            mInflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);        }         public void addItem(final String item) {            mData.add(item);            notifyDataSetChanged();        }         public void addSeparatorItem(final String item) {            mData.add(item);            // save separator position            mSeparatorsSet.add(mData.size() - 1);            notifyDataSetChanged();        }         @Override        public int getItemViewType(int position) {            return mSeparatorsSet.contains(position) ? TYPE_SEPARATOR : TYPE_ITEM;        }         @Override        public int getViewTypeCount() {            return TYPE_MAX_COUNT;        }         @Override        public int getCount() {            return mData.size();        }         @Override        public String getItem(int position) {            return mData.get(position);        }         @Override        public long getItemId(int position) {            return position;        }         @Override        public View getView(int position, View convertView, ViewGroup parent) {            ViewHolder holder = null;            int type = getItemViewType(position);            System.out.println("getView " + position + " " + convertView + " type = " + type);            if (convertView == null) {                holder = new ViewHolder();                switch (type) {                    case TYPE_ITEM:                        convertView = mInflater.inflate(R.layout.item1, null);                        holder.textView = (TextView)convertView.findViewById(R.id.text);                        break;                    case TYPE_SEPARATOR:                        convertView = mInflater.inflate(R.layout.item2, null);                        holder.textView = (TextView)convertView.findViewById(R.id.textSeparator);                        break;                }                convertView.setTag(holder);            } else {                holder = (ViewHolder)convertView.getTag();            }            holder.textView.setText(mData.get(position));            return convertView;        }     }     public static class ViewHolder {        public TextView textView;    }}

Let’s run what we wrote. Yo will see separators after each 4-th item in the list.

In the log – nothing exceptional – all convertView is null for visible items both types.

02-05 15:19:03.080: INFO/System.out(1035): getView 0 null type = 002-05 15:19:03.112: INFO/System.out(1035): getView 1 null type = 002-05 15:19:03.130: INFO/System.out(1035): getView 2 null type = 002-05 15:19:03.141: INFO/System.out(1035): getView 3 null type = 002-05 15:19:03.160: INFO/System.out(1035): getView 4 null type = 102-05 15:19:03.170: INFO/System.out(1035): getView 5 null type = 002-05 15:19:03.180: INFO/System.out(1035): getView 6 null type = 002-05 15:19:03.190: INFO/System.out(1035): getView 7 null type = 002-05 15:19:03.210: INFO/System.out(1035): getView 8 null type = 002-05 15:19:03.210: INFO/System.out(1035): getView 9 null type = 1

Scroll list and see what happens:

02-05 15:19:54.160: INFO/System.out(1035): getView 10 null type = 002-05 15:19:57.440: INFO/System.out(1035): getView 11 android.widget.LinearLayout@43744528 type = 002-05 15:20:01.310: INFO/System.out(1035): getView 12 android.widget.LinearLayout@43744eb0 type = 002-05 15:20:01.880: INFO/System.out(1035): getView 13 android.widget.LinearLayout@437456d8 type = 002-05 15:20:02.869: INFO/System.out(1035): getView 14 null type = 102-05 15:20:06.489: INFO/System.out(1035): getView 15 android.widget.LinearLayout@43745f00 type = 002-05 15:20:07.749: INFO/System.out(1035): getView 16 android.widget.LinearLayout@43747170 type = 002-05 15:20:10.250: INFO/System.out(1035): getView 17 android.widget.LinearLayout@43747998 type = 002-05 15:20:11.661: INFO/System.out(1035): getView 18 android.widget.LinearLayout@437481c0 type = 002-05 15:20:13.180: INFO/System.out(1035): getView 19 android.widget.LinearLayout@437468a0 type = 102-05 15:20:16.900: INFO/System.out(1035): getView 20 android.widget.LinearLayout@437489e8 type = 002-05 15:20:25.690: INFO/System.out(1035): getView 21 android.widget.LinearLayout@4374a8d8 type = 0

convertView is null for separator view type until first separator is visible. When it goes off the screen – view also comes to the Recycler and convertView comes to play.