DataSetObserver猜想觀察者模式

frameworks/base/core/java/android/database/DataSetObserver.java

此類的所有代碼為：

public abstract class DataSetObserver{

    public void onChanged(){}

    public void onInvalidated(){}

}

我在想，誰調用onChanged呢？對於觀察者，當數據變動時調用onChanged()吧，那應該有數據變動的地方，insert / update /delete

frameworks/base/core/java/android/widget/AdapterView.java內部類AdapterDataSetObserver繼承了此類，但它也只是重寫了此類中的兩個方法，沒有寫調用關系。

 

frameworks/base/core/java/android/database/DataSetObserverable.java

此類的所有代碼

public class DataSetObservable extends Observable<DataSetObserver> {
    /** 
     * Invokes onChanged on each observer. Called when the data set being observed has
     * changed, and which when read contains the new state of the data.
     */
    public void notifyChanged() {
        synchronized(mObservers) {
            for (DataSetObserver observer : mObservers) {
                observer.onChanged();
            }   
        }   
    }   

    /** 
     * Invokes onInvalidated on each observer. Called when the data set being monitored
     * has changed such that it is no longer valid.
     */
    public void notifyInvalidated() {
        synchronized (mObservers) {
            for (DataSetObserver observer : mObservers) {
                observer.onInvalidated();
            }   
        }   
    }
}

 

public abstract class Observable<T> {
    /**
     * The list of observers.  An observer can be in the list at most
     * once and will never be null.
     */
    protected final ArrayList<T> mObservers = new ArrayList<T>();

    /**
     * Adds an observer to the list. The observer cannot be null and it must not already
     * be registered.
     * @param observer the observer to register
     * @throws IllegalArgumentException the observer is null
     * @throws IllegalStateException the observer is already registered
     */
    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 abstract class BaseAdapter implements ListAdapter, SpinnerAdapter {
    private final DataSetObservable mDataSetObservable = new DataSetObservable();

    public boolean hasStableIds() {
        return false;
    }
    
    public void registerDataSetObserver(DataSetObserver observer) {
        mDataSetObservable.registerObserver(observer);
    }

    public void unregisterDataSetObserver(DataSetObserver observer) {
        mDataSetObservable.unregisterObserver(observer);
    }
    
    /**
     * Notifies the attached View that the underlying data has been changed
     * and it should refresh itself.
     */
    public void notifyDataSetChanged() {
        mDataSetObservable.notifyChanged();
    }
    
    public void notifyDataSetInvalidated() {
        mDataSetObservable.notifyInvalidated();
    }
...
}

從類BaseAdapter中看，這里的注冊和通知動作都是通過DataSetObservable對象的，而DataSetObservable繼承了Observable<DataSetObserver>。

 因此，要查找那些繼承自BaseAdapter，又重寫了DataSetObserver的onChanged的函數。