适配器(Adapter)详述:http://www.php.cn/java-article-355851.html
观察者(Observer)详述:http://www.php.cn/java-article-356024.html
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 extends Observable4864d1769940fac3918b0cc0f2557122 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; @Override public 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(); } @Override public 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 restarted mInstanceState = AdapterView.this.onSaveInstanceState(); } // Data is invalid so we should reset our state mOldItemCount = 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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