适配器(Adapter)详述：
观察者(Observer)详述：
AdapterView 体系
AdapterView中会使用Adapter
Adapter 体系
BaseAdapter 实现了 SpinnerAdapter、ListAdapter
这样的形式，就是 适配器模式的应用， 这里是采用的是 接口适配器
观察者(Observer) 模式
在Adapter中定义了注册和反注册DataSetObserver的方法
public interface Adapter {void registerDataSetObserver(DataSetObserver observer);void unregisterDataSetObserver(DataSetObserver observer);…}public abstract class DataSetObserver {public void onChanged() {// Do nothing}public void onInvalidated() {// Do nothing}}public abstract class BaseAdapter implements ListAdapter, SpinnerAdapter {private final DataSetObservable mDataSetObservable = new DataSetObservable();public void registerDataSetObserver(DataSetObserver observer) {mDataSetObservable.registerObserver(observer);}public void unregisterDataSetObserver(DataSetObserver observer) {mDataSetObservable.unregisterObserver(observer);}public void notifyDataSetChanged() {mDataSetObservable.notifyChanged();}public void notifyDataSetInvalidated() {mDataSetObservable.notifyInvalidated();}…}public class DataSetObservable extends Observable<DataSetObserver> {public void notifyChanged() {synchronized(mObservers) {for (int i = mObservers.size() – 1; i >= 0; i–) {mObservers.get(i).onChanged();}}}public void notifyInvalidated() {synchronized (mObservers) {for (int i = mObservers.size() – 1; i >= 0; i–) {mObservers.get(i).onInvalidated();}}}}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 unregisterAll() {synchronized(mObservers) {mObservers.clear();}}}DataSetObserver 观察者（观察数据集：发生变化onChanged、无效onInvalidated）
Observable 处理观察者（添加、移除、注册、反注册）
DataSetObservable extendsObservable<DataSetObserver> 添加了通知数据改变和无效的 两个方法
在AdapterView中
class AdapterDataSetObserver extends DataSetObserver {private Parcelable mInstanceState = null;@Overridepublic void onChanged() {mDataChanged = true;mOldItemCount = mItemCount;mItemCount = getAdapter().getCount();// Detect the case where a cursor that was previously invalidated has// been repopulated with new data.if (AdapterView.this.getAdapter().hasStableIds() && mInstanceState != null&& mOldItemCount == 0 && mItemCount > 0) {AdapterView.this.onRestoreInstanceState(mInstanceState);mInstanceState = null;} else {rememberSyncState();}checkFocus();requestLayout();}@Overridepublic void onInvalidated() {mDataChanged = true;if (AdapterView.this.getAdapter().hasStableIds()) {// Remember the current state for the case where our hosting activity is being// stopped and later restartedmInstanceState = AdapterView.this.onSaveInstanceState();}// Data is invalid so we should reset our statemOldItemCount = mItemCount;mItemCount = 0;mSelectedPosition = INVALID_POSITION;mSelectedRowId = INVALID_ROW_ID;mNextSelectedPosition = INVALID_POSITION;mNextSelectedRowId = INVALID_ROW_ID;mNeedSync = false;checkFocus();requestLayout();}public void clearSavedState() {mInstanceState = null;}}
自定义了AdapterDataSetObserver，在两个实现方法中都调用了requestLayout()，重新设置layout
整个观察数据变化导致界面改变的流程：1. 在AdapterView体系中 自定义AdapterDataSetObserver，并注册(即添加observer到observable)。
2. 在调用adapter.notifyDataSetChanged()后，内部执行observable的notifyChanged()，
将执行每一个observer的onChanged()，也就达到了更新界面的效果。
notifyDataSetInvalidated同理
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自己不喜欢的人，可以报之以沉默微笑；
