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 {
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 {
protected final ArrayList mObservers = new ArrayList();
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
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