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。