AsyncTask的参数分析

最新推荐文章于 2021-09-11 11:07:18 发布

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最新推荐文章于 2021-09-11 11:07:18 发布

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分类专栏： Android应用

本文链接：https://blog.youkuaiyun.com/xifens/article/details/38405767

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本文深入探讨了AsyncTask的使用方法，详细解释了三个泛型参数的作用，包括Params、Progress和Result，并通过实例展示了如何在UI线程前预执行任务，后台线程执行计算操作，以及UI线程后的执行操作。同时，阐述了如何在执行过程中发布进度更新。

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AsyncTask的使用：

new MyTask().execute(Params...params);
AsyncTask的三个泛型参数说明（三个参数可以是任何类型）
1. 第一个参数Params：传入doInBackground()方法的参数类型
2. 第二个参数Progress：传入onProgressUpdate()方法的参数类型
3. 第三个参数Result：传入onPostExecute()方法的参数类型，也是doInBackground()方法返回的类型

private class MyTask extends AsyncTask<Params, Progress, Result> {
    
    /*
     * Runs on the UI thread before doInBackground(Params...)
     */
    protected void onPreExecute (){
        ...
    }
    
/*
 * Override this method to perform a computation on a background thread. 
 * The specified parameters are the parameters passed to execute(Params...)
 * by the caller of this task.This method can call publishProgress(Progress...)
 * to publish updates on the UI thread.
 */
    protected Result doInBackground (Params... params){
        ...
    }
    
/*
 * Runs on the UI thread after doInBackground(Params...). 
 * The specified result is the value returned by doInBackground(Params...).
 * This method won't be invoked if the task was cancelled.
 * Parameters result:The result of the operation computed by doInBackground(Params...).
 */
    protected void onPostExecute (Result result){
        ...
    }
    
/*
 * Runs on the UI thread after publishProgress(Progress...) is invoked. 
 * The specified values are the values passed to publishProgress(Progress...).
 */
    protected void onProgressUpdate (Progress... values) {
        ...
    }
    
 /*
  * This method can be invoked from doInBackground(Params...) to publish updates
  * on the UI thread while the background computation is still running. 
  * Each call to this method will trigger the execution of 
  * onProgressUpdate(Progress...) on the UI thread. onProgressUpdate(Progress...)
  *  will not be called if the task has been canceled.
  */
    protected final void publishProgress (Progress... values) {
        ...
    }
   
/* 
 * Runs on the UI thread after cancel(boolean) is invoked and doInBackground(Object[])
 *  has finished.The default implementation simply invokes onCancelled()
 *  and ignores the result.If you write your own implementation, 
 *  do not call super.onCancelled(result).
 */
    protected void onCancelled (Result result) {
       ...
    }
}