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ListView要想显示数据，需要用到数据适配器即Adapter。而当我们删除ListView的某个条目时，数据适配器中的数据源必然发生改变，这时候我们通过调用适配器类提供的notifyDataSetChanged方法通知listview数据发生改变，请求重新绘制。
public void notifyDataSetChanged() {
mDataSetObservable.notifyChanged();
}这个mDataSetObservable即被观察的对象，它是一个DataSetObservable类型。我们来看下其实现：package android.database;
public class DataSetObservable extends Observable<DataSetObserver> {
public void notifyChanged() {
synchronized(mObservers) {
for (int i = mObservers.size() - 1; i >= 0; i--) {
mObservers.get(i).onChanged();
}
}
}
}
package android.database;
import java.util.ArrayList;
public abstract class Observable<T> {
protected final ArrayList<T> mObservers = new ArrayList<T>();
public void registerObserver(T observer) {
if (observer == null) {
throw new IllegalArgumentException("The observer is null.");
}
synchronized(mObservers) {
if (mObservers.contains(observer)) {
throw new IllegalStateException("Observer " + observer + " is already registered.");
}
mObservers.add(observer);
}
}
public void unregisterObserver(T observer) {
if (observer == null) {
throw new IllegalArgumentException("The observer is null.");
}
synchronized(mObservers) {
int index = mObservers.indexOf(observer);
if (index == -1) {
throw new IllegalStateException("Observer " + observer + " was not registered.");
}
mObservers.remove(index);
}
}
...
}
public void setAdapter(ListAdapter adapter) {
... ...
super.setAdapter(adapter);
if (mAdapter != null) {
... ...
mDataSetObserver = new AdapterDataSetObserver();
mAdapter.registerDataSetObserver(mDataSetObserver);
... ...
} else {
... ...
}
requestLayout();
}果然，在这个方法中我们找到了注册观察者的代码，但是这里的观察者是AdapterDataSetObserver类型的，而Adapter要求的是DataSetObserver类型的，那么很显然，AdapterDataSetObserver是DataSetObserver的子类。该类的定义在ListView的父类AbsListView中：class AdapterDataSetObserver extends AdapterView<ListAdapter>.AdapterDataSetObserver {
@Override
public void onChanged() {
super.onChanged();
if (mFastScroller != null) {
mFastScroller.onSectionsChanged();
}
}
... ...
}而AbsListView中的AdapterDataSetObserver又继承了AdapterView类中的AdapterDataSetObserver。最终，我们再AdapterView中找到AdapterDataSetObserver： class AdapterDataSetObserver extends DataSetObserver {
private Parcelable mInstanceState = null;
@Override
public void onChanged() {
mDataChanged = true;
mOldItemCount = mItemCount;
mItemCount = getAdapter().getCount();
if (AdapterView.this.getAdapter().hasStableIds() && mInstanceState != null
&& mOldItemCount == 0 && mItemCount > 0) {
AdapterView.this.onRestoreInstanceState(mInstanceState);
mInstanceState = null;
} else {
rememberSyncState();
}
checkFocus();
requestLayout();
}
... ...
}
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原文地址：http://blog.csdn.net/chdjj/article/details/42293681
