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Rules::The AsyncTask instance must be created in UI thread. .execute must be invoked on the UI thread.Never call  objMyTask.onPreExecute(), objMyTask.doInBackground(), objMyTask.onProgressUpdate(),  objMyTask.onPostExecute manually.The AsyncTask can be executed only once (an exception will be thrown if a second execution is attempted.)AsyncTask have Four Main Method... onPreExecute()  doInBackground() onProgressUpdate() onPostExecute()  onPreExecute-This method is called first when you start AsyncTask using objAsync.execute().And mostly this method is use for initializing dialog(ProgressDialog,CustomDialog) and showing. doInBackground-The main purpose of AsyncTask is accomplished by this method.Any non-UI thread process is running in this method.Such as Rss Feed Reader,Image and video Uploading and Downloading.You cant handle your View in this method.Because this method is non-UI thread.While any background process is running if you want to handle UI therea are  onProgressUpdate method. after completion of process this method send result to OnPostExecute. onProgressUpdate-While backgrounding task is running ,you can handle your UI using this method .Such as status of downloading or uploading task.and this method is called from  doInBackground.Using publishProgress() you can call onProgressUpdate method to update UI while process is running. onPostExecute -This method is called after the background computation finishes.The result of background process in passed in this method as parameters.And now you can dismiss progress dialog ,to indicate that background task is completed. You can cancel AsyncTask using objAsyncTask.cancel().then you just check in doInBackground, if (isCancelled()) { break; } else {        //continue... } See this Image For more Clear.

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从蓝牙4.0开始包含两个蓝牙芯片模块：传统/经典蓝牙模块(Classic Bluetooth,简称BT)和低功耗蓝牙(Bluetooth Low Energy,简称BLE) 经典蓝牙是在之前的蓝牙1.0,1.2,2.0 EDR,2.1 EDR,3.0 EDR等基础上发展和完善起来的, 而低功耗蓝牙是Nokia的Wibree标准上发展起来的，是完全不同两个标准。1.经典蓝牙模块(BT)泛指蓝牙4.0以下的模块，一般用于数据量比较大的传输，如：语音、音乐、较高数据量传输等。经典蓝牙模块可再细分为：传统蓝牙模块和高速蓝牙模块。传统蓝牙模块在2004年推出，主要代表是支持蓝牙2.1协议的模块，在智能手机爆发的时期得到广泛支持。高速蓝牙模块在2009年推出，速率提高到约24Mbps，是传统蓝牙模块的八倍。 传统蓝牙有3个功率级别，Class1,Class2,Class3,分别支持100m,10m,1m的传输距离2.低功耗蓝牙模块(BLE)泛指蓝牙4.0或更高的模块，蓝牙低功耗技术是低成本、短距离、可互操作的鲁棒性无线技术，工作在免许可的2.4GHz ISM射频频段。因为BLE技术采用非常快速的连接方式，因此平时可以处于“非连接”状态（节省能源），此时链路两端相互间只是知晓对方，只有在必要时才开启链路，然后在尽可能短的时间内关闭链路(每次最多传输20字节)。低功耗蓝牙无功率级别，一般发送功率在7dBm，一般在空旷距离，达到20m应该是没有问题