Android 适配器(Adapter)、观察者(Observer) 形式

适配器(Adapter)详述：http://blog.csdn.net/jjwwmlp456/article/details/39893723

观察者(Observer)详述：http://blog.csdn.net/jjwwmlp456/article/details/39967021

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();        }    }}

Observable 处理观察者（添加、移除、注册、反注册）

DataSetObservable extends Observable<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;        @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  

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