Android Loader使用时，屏幕解锁后，重复加载

在使用AsyncTaskLoader时，当手机解锁后，会重复加载数据，代码如下：

static class CouponShopQueryLoader extends
AsyncTaskLoader<List<CouponStore>> {private int couponId;public CouponShopQueryLoader(Context context, int couponId) {
super(context);
this.couponId = couponId;}@Override
protected void onStartLoading() {forceLoad();
}@Override
public List<CouponStore> loadInBackground() {
//查询数据加载
}
}

这时候，很奇怪的现象就出来了，每次手机解锁后，数据都会重复了，重复加载。经查阅CursorLoader源码后发现，原来还是自己太嫩了，loader使用时，没有严格遵守android官方帮助文档demo的使用方式。经修改后：

static class CouponShopQueryLoader2 extends
AsyncTaskLoader<List<CouponStore>> {private List<CouponStore> mData;
private int couponId;public CouponShopQueryLoader2(Context context, int couponId) {
super(context);
this.couponId = couponId;}// final ForceLoadContentObserver mObserver;/* Runs on a worker thread */
@Override
public List<CouponStore> loadInBackground() {
mData = ds.queryShopByCoupon(couponId, pageNo, PAGE_SIZE);
return mData;
}/* Runs on the UI thread */
@Override
public void deliverResult(List<CouponStore> data) {
if (isReset()) {
return;
}if (isStarted()) {
super.deliverResult(data);
}
}/**
* Starts an asynchronous load of the contacts list data. When the
* result is ready the callbacks will be called on the UI thread. If a
* previous load has been completed and is still valid the result may be
* passed to the callbacks immediately.
*
* Must be called from the UI thread
*/
@Override
protected void onStartLoading() {
if (mData != null) {
deliverResult(mData);
}
if (takeContentChanged() || mData == null) {
forceLoad();
}
}/**
* Must be called from the UI thread
*/
@Override
protected void onStopLoading() {
Log.d("sss", "onStopLoading");
// Attempt to cancel the current load task if possible.
cancelLoad();
}@Override
public void onCanceled(List<CouponStore> cursor) {
Log.d("sss", "onCanceled");
}@Override
protected void onReset() {
super.onReset();
Log.d("sss", "onReset");
// Ensure the loader is stopped
onStopLoading();
mData = null;
}}

修改后，重复加载的现象解决了，究其原因是没有重写

/**
* Must be called from the UI thread
*/
@Override
protected void onStopLoading() {
Log.d("sss", "onStopLoading");
// Attempt to cancel the current load task if possible.
cancelLoad();
}

当手机屏幕关闭时，会调用onStopLoading（）方法，此时应该将loader取消掉，当屏幕解锁时，会去执行onStartLoading（）方法，在onStartLoading方法中根据数据是否需要重新加载进行判断。而如果不在onStartLoading进行loader状态判断的话，就导致了数据重复加载的问题！ ok---解决了！

提示：在学习android开发中，官方文档其实是很好的，遵守他们的编写规范，可以使自己少走好多弯路。