適配器(Adapter)詳述:http://www.php.cn/java-article-355851.html
觀察者(Observer)詳述:http://www.php.cn /java-article-356024.html
AdapterView 系統
AdapterView中會使用Adapter
#Adapter 系統
BaseAdapter 實作了SpinnerAdapter、ListAdapter
BaseAdapter 實作了SpinnerAdapter、ListAdapter
這樣的形式,就是適配器模式的應用, 這裡是採用的是 介面適配器
觀察者(Observer) 模式
在Adapter中定義了註冊和反註冊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 觀察者(觀察資料集:變更onChanged、無效onInvalidated)
Observable 處理觀察者(新增、移除、註冊、反註冊)
DataSetObservable extends Observable4864d1769940fac3918b0cc0f2557122 新增了兩個通知資料變更和無效的方法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; } }自訂了AdapterDataSetObserver,在兩個實作方法中都呼叫了requestLayout(),重新設定layout
2. 在呼叫adapter.notifyDataSetChanged()後,內部執行observable的notifyChanged(),
將執行每一個observer的onChanged(),也就達到了更新介面的效果。
### notifyDataSetInvalidated同理#######以上是Android適配器(Adapter)、觀察者(Observer) 模式的程式碼分析(圖)的詳細內容。更多資訊請關注PHP中文網其他相關文章!