Android 適配器(Adapter)、觀察者(Observer) 模式，androidobserver

Android 適配器(Adapter)、觀察者(Observer) 模式，androidobserver

適配器(Adapter)詳述：http://blog.csdn.net/jjwwmlp456/article/details/39893723

觀察者(Observer)詳述：http://blog.csdn.net/jjwwmlp456/article/details/39967021

AdapterView 體系

  AdapterView中會使用Adapter

Adapter 體系

  BaseAdapter 實現了 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：發生變化onChanged、無效onInvalidated）

Observable 處理觀察者（添加、移除、註冊、反註冊）

DataSetObservable extends Observable<DataSetObserver>   添加了通知數據改變和無效的 兩個方法

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;        }    }

   自訂了AdapterDataSetObserver，在兩個實現方法中都調用了requestLayout()，重新設定layout  

整個觀察資料變化導致介面改變的流程：
1.  在AdapterView體系中 自訂 AdapterDataSetObserver，並註冊(即添加observer到observable)。

2.  在調用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

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