ListView中有不同的ViewType，它的convertView實現

a_long_總結：

只要在繼承BaseAdapter的MyAdapter中完成以下3點：

1：重寫getViewTypeCount()-總共的Type數量；

2：重寫getItemViewType(int)-由position來得知Type的id；

3：根據Type在getView中正確的創建convertView；

那麼Adapter會調用getTimeViewType方法來判斷這個View的類型，從而當View被Recycler回收後，Adapter會自動根據View的Type而正確的返回是否有convertView或者是convertView==null。

這樣就實現了一個ListView中有不同的ViewType，而每一個View都被正確的convert（VIewHolder）了，優化性能。

示例代碼如下：

參考自：

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 = 0
02-05 15:19:03.112: INFO/System.out(1035): getView 1 null type = 0
02-05 15:19:03.130: INFO/System.out(1035): getView 2 null type = 0
02-05 15:19:03.141: INFO/System.out(1035): getView 3 null type = 0
02-05 15:19:03.160: INFO/System.out(1035): getView 4 null type = 1
02-05 15:19:03.170: INFO/System.out(1035): getView 5 null type = 0
02-05 15:19:03.180: INFO/System.out(1035): getView 6 null type = 0
02-05 15:19:03.190: INFO/System.out(1035): getView 7 null type = 0
02-05 15:19:03.210: INFO/System.out(1035): getView 8 null type = 0
02-05 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 = 0
02-05 15:19:57.440: INFO/System.out(1035): getView 11 android.widget.LinearLayout@43744528 type = 0
02-05 15:20:01.310: INFO/System.out(1035): getView 12 android.widget.LinearLayout@43744eb0 type = 0
02-05 15:20:01.880: INFO/System.out(1035): getView 13 android.widget.LinearLayout@437456d8 type = 0
02-05 15:20:02.869: INFO/System.out(1035): getView 14 null type = 1
02-05 15:20:06.489: INFO/System.out(1035): getView 15 android.widget.LinearLayout@43745f00 type = 0
02-05 15:20:07.749: INFO/System.out(1035): getView 16 android.widget.LinearLayout@43747170 type = 0
02-05 15:20:10.250: INFO/System.out(1035): getView 17 android.widget.LinearLayout@43747998 type = 0
02-05 15:20:11.661: INFO/System.out(1035): getView 18 android.widget.LinearLayout@437481c0 type = 0
02-05 15:20:13.180: INFO/System.out(1035): getView 19 android.widget.LinearLayout@437468a0 type = 1
02-05 15:20:16.900: INFO/System.out(1035): getView 20 android.widget.LinearLayout@437489e8 type = 0
02-05 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.