Android Loader使用時，屏幕解鎖後，重複加載

在使用AsyncTaskLoader時，當手機解鎖後，會重複加載數據，代碼以下：

	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() {
			//查詢數據加載
		}
	}

這時候，很奇怪的現象就出來了，每次手機解鎖後，數據都會重複了，重複加載。經查閱CursorLoader源碼後發現，原來仍是本身太嫩了，loader使用時，沒有嚴格遵照android官方幫助文檔demo的使用方式。經修改後：

	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;
		}

	}

修改後，重複加載的現象解決了，究其緣由是沒有重寫

	/**
		 * 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();
		}

當手機屏幕關閉時，會調用onStopLoading（）方法，此時應該將loader取消掉，當屏幕解鎖時，會去執行onStartLoading（）方法，在onStartLoading方法中根據數據是否須要從新加載進行判斷。而若是不在onStartLoading進行loader狀態判斷的話，就致使了數據重複加載的問題！ ok---解決了！

提示：在學習android開發中，官方文檔實際上是很好的，遵照他們的編寫規範，能夠使本身少走好多彎路。