ListView中使用自定义Adapter及时更新数据
2012-11-27 23:59 2946 0
在项目中，遇到不能ListView及时更新的问题。写了一个demo，其中也遇到一些问题，一并写出来。好吧，上代码：
public class PersonAdapter extends BaseAdapter {
private ArrayList<PersonBean> mList;
private Context mContext;
public PersonAdapter(ArrayList<PersonBean> list, Context context) {
mList = list;
mContext = context;
}
public void refresh(ArrayList<PersonBean> list) {
mList = list;
notifyDataSetChanged();
}
@Override
public int getCount() {
return mList.size();
}
@Override
public Object 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) {
Holder holder = null;
if (convertView == null) {
LayoutInflater inflater = LayoutInflater.from(mContext);
convertView = inflater.inflate(R.layout.list_item, null);
holder = new Holder();
holder.mNameText = (TextView)convertView.findViewById(R.id.name_text);
holder.mIDText = (TextView)convertView.findViewById(R.id.id_text);
convertView.setTag(holder);
} else {
holder = (Holder) convertView.getTag();
}
holder.mNameText.setText(mList.get(getCount() - position - 1).getName());
holder.mIDText.setText(mList.get(getCount() - position - 1).getID());
return convertView;
}
class Holder {
private TextView mNameText, mIDText;
}
}
PersonAdapter继承自BaseAdapter，里面的代码都应该比较熟悉。里面注意这点代码：
public void refresh(ArrayList<PersonBean> list) {
mList = list;
notifyDataSetChanged();
}
在初始化PersonAdapter的时候，需要外部导入一个mList。
public PersonAdapter(ArrayList<PersonBean> list, Context context) {
mList = list;
mContext = context;
}
在使用这种类型时，在Activity使用mAdapter.notifyDataSetChanged()时候，有时候会发现数据不能够及时的更新。这个时候，就比较需要调用refresh()这个方法了。
下面看一下主Activity：
public class ListViewRefreshActivity extends Activity {
private ListView mListView;
private ArrayList<PersonBean> mList;
private PersonAdapter mAdapter;
private Handler mHandler;
private String mName, mID;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mListView = (ListView)findViewById(R.id.listView);
mList = new ArrayList<PersonBean>();
mAdapter = new PersonAdapter(mList, ListViewRefreshActivity.this);
mListView.setAdapter(mAdapter);
mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
mList.add((PersonBean) msg.obj);
Log.v("@@@@@@", "this is get message");
mAdapter.refresh(mList);
// mAdapter.notifyDataSetChanged();
}
};
// final Message message = new Message();
new Thread(new Runnable() {
@Override
public void run() {
try {
for (int i = 0; i < 10; i++) {
mName = "hao :" + i;
mID = "" + i;
PersonBean bean = new PersonBean();
bean.setID(mID);
bean.setName(mName);
Message message = new Message();
message.obj = bean;
Thread.sleep(3000);
mHandler.sendMessage(message);
// mHandler.sendMessageDelayed(message, 10000);
}}catch (Exception e) {
e.printStackTrace();
}
}
}).start();
}
}
先说一个小bug吧，看一下在new Thread上面有一句注释掉的
final Message message = new Message();
如果用这个message，注释run方法体内的message，运行程序，在我机子上，发送第四个消息时，就会报android.util.AndroidRuntimeException:This message is already in use这个错，message已经被使用。所以，每一次发送，都要重新创建一个新的message。也可以使用一下语句：
message = mHandler.obtainMessage();
里面主要看一下handler中重写handlerMessage这个方法：
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
mList.add((PersonBean) msg.obj);
Log.v("@@@@@@", "this is get message");
mAdapter.refresh(mList);
// mAdapter.notifyDataSetChanged();
}
当然，在这个小例子中，使用mAdapter.refresh这个方法更麻烦点，直接调用notifyDataSetChange就可以达到效果，如果你的代码里面不能达到效果，就可以使用mAdapter.refresh试一下。
notifyDataSetChanged这个方法的设计是典型观察者模式。看一下源代码：
public abstract class BaseAdapter implements ListAdapter, SpinnerAdapter {
private final DataSetObservable mDataSetObservable = new DataSetObservable();
public boolean hasStableIds() {
return false;
}
public void registerDataSetObserver(DataSetObserver observer) {
mDataSetObservable.registerObserver(observer);
}
public void unregisterDataSetObserver(DataSetObserver observer) {
mDataSetObservable.unregisterObserver(observer);
}
/**
* Notifies the attached observers that the underlying data has been changed
* and any View reflecting the data set should refresh itself.
*/
public void notifyDataSetChanged() {
mDataSetObservable.notifyChanged();
}
/**
* Notifies the attached observers that the underlying data is no longer valid
* or available. Once invoked this adapter is no longer valid and should
* not report further data set changes.
*/
public void notifyDataSetInvalidated() {
mDataSetObservable.notifyInvalidated();
}
有一个数据被观察者：mDataSetObservable。当被观察者数据发生改变时，通知观察者。我们使用registerDataSetObserver这个方法注册观察者。都是调用notifyDataSetChanged方法。就是告诉观察者，数据有所改变。在这个方法中，又调用了DataSetObserveable的notifyChanged方法：
/**
* Invokes onChanged on each observer. Called when the data set being observed has
* changed, and which when read contains the new state of the data.
*/
public void notifyChanged() {
synchronized(mObservers) {
// since onChanged() is implemented by the app, it could do anything, including
// removing itself from {@link mObservers} - and that could cause problems if
// an iterator is used on the ArrayList {@link mObservers}.
// to avoid such problems, just march thru the list in the reverse order.
for (int i = mObservers.size() - 1; i >= 0; i--) {
mObservers.get(i).onChanged();
}
}
}
看一下他的方法说明：当数据被观察到已经改变，调用每一个观察者的onChanged方法去读取数据的最新状态。
mObservers的定义如下：
protected final ArrayList<T> mObservers = new ArrayList<T>();
通过遍历一个ArrayList来通知各个观察者。
前面说到了，我们可以调用registerDataSetObserver注册为观察者，但是是在哪注册的呢？因为如果没有注册，adapter就不应该发生变化。所以，我们看下ListView的SetAdapter这个方法：
@Override
public void setAdapter(ListAdapter adapter) {
if (mAdapter != null && mDataSetObserver != null) {
mAdapter.unregisterDataSetObserver(mDataSetObserver);
}
resetList();
mRecycler.clear();
if (mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0) {
mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, adapter);
} else {
mAdapter = adapter;
}
mOldSelectedPosition = INVALID_POSITION;
mOldSelectedRowId = INVALID_ROW_ID;
// AbsListView#setAdapter will update choice mode states.
super.setAdapter(adapter);
if (mAdapter != null) {
mAreAllItemsSelectable = mAdapter.areAllItemsEnabled();
mOldItemCount = mItemCount;
mItemCount = mAdapter.getCount();
checkFocus();
mDataSetObserver = new AdapterDataSetObserver();
mAdapter.registerDataSetObserver(mDataSetObserver);
mRecycler.setViewTypeCount(mAdapter.getViewTypeCount());
int position;
if (mStackFromBottom) {
position = lookForSelectablePosition(mItemCount - 1, false);
} else {
position = lookForSelectablePosition(0, true);
}
setSelectedPositionInt(position);
setNextSelectedPositionInt(position);
if (mItemCount == 0) {
// Nothing selected
checkSelectionChanged();
}
} else {
mAreAllItemsSelectable = true;
checkFocus();
// Nothing selected
checkSelectionChanged();
}
requestLayout();
}
如果mAdapter和mDataSetObserver都不为空的话，取消mAdapter对mDataSetObserver的注册。
if (mAdapter != null && mDataSetObserver != null) {
mAdapter.unregisterDataSetObserver(mDataSetObserver);
}
然后，把传入的adapter这个参数，赋值给mAdapter：
if (mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0) {
mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, adapter);
} else {
mAdapter = adapter;
}
赋值成功后：
if (mAdapter != null) {
mDataSetObserver = new AdapterDataSetObserver();
mAdapter.registerDataSetObserver(mDataSetObserver);
重新为mDataSetObserver赋值，然后把mAdapter注册为mDataSetObserver的观察者。
至此，思路应该清晰了：在listview的setAdapter中把adapter注册为mDataSetObserver的观察者。当数据变化时，就可以调用notifyDataSetChanged方法来提示观察者数据已经变化。
最后就是说一下，里面PersonBean类，就是一个实体类，很简单，不在详述。
最后，源代码：http://download.csdn.net/detail/aomandeshangxiao/4704585
