Android的AsyncTask的例子和说明 [英] Android AsyncTask example and explanation

问题描述

我想使用的AsyncTask 在我的应用程序，但我无法找到一个code段与事物是如何工作的一个简单的解释。我只是想要的东西帮我拿回去的速度很快，而不必涉水通过文档或大量的Q＆放大器;至于一次。

I want to use an AsyncTask in my app but I am having trouble finding a code snippet with a simple explanation of how things work. I just want something to help me get get back up to speed quickly without having to wade through the documentation or lots of Q&As again.

推荐答案

下面是一个骨骼code与说明概要：

Code:

Here is a skeletal code outline with explanations:

public class AsyncTaskTestActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);  

        // This starts the AsyncTask
        // Doesn't need to be in onCreate()
        new MyTask().execute("my string paramater");
    }

    // Here is the AsyncTask class:
    //
    // AsyncTask<Params, Progress, Result>.
    //    Params – the type (Object/primitive) you pass to the AsyncTask from .execute() 
    //    Progress – the type that gets passed to onProgressUpdate()
    //    Result – the type returns from doInBackground()
    // Any of them can be String, Integer, Void, etc. 

    private class MyTask extends AsyncTask<String, Integer, String> {

        // Runs in UI before background thread is called
        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            // Do something like display a progress bar
        }

        // This is run in a background thread
        @Override
        protected String doInBackground(String... params) {
            // get the string from params, which is an array
            String myString = params[0];

            // Do something that takes a long time, for example:
            for (int i = 0; i <= 100; i++) {

                // Do things

                // Call this to update your progress
                publishProgress(i);
            }

            return "this string is passed to onPostExecute";
        }

        // This is called from background thread but runs in UI
        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);

            // Do things like update the progress bar
        }

        // This runs in UI when background thread finishes
        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);

            // Do things like hide the progress bar or change a TextView
        }
    }
}

流图：

下面是用于帮助说明，所有的参数和类型会：

Flow Diagram:

Here is a diagram to help explain where all the parameters and types are going:

• <一个href="http://stackoverflow.com/questions/6053602/what-arguments-are-passed-into-asynctaskarg1-arg2-arg3">What参数传递到AsyncTask的＆LT; ARG1，ARG2，ARG3＆GT ;?
• Slidenerd的Andr​​oid AsyncTask的教程：Android的初学者教程
• 安卓：为什么，何时以及如何使用AsyncTask的使用例子
• <一个href="http://androidresearch.word$p$pss.com/2012/03/17/understanding-asynctask-once-and-forever/">Understanding AsyncTask的 - 一劳永逸
• <一个href="http://androidresearch.word$p$pss.com/2013/05/10/dealing-with-asynctask-and-screen-orientation/">Dealing与AsyncTask的和屏幕方向
• 如何将多个参数传递给AsynkTask
• <一个href="http://stackoverflow.com/questions/17989914/how-to-pass-in-two-different-data-types-to-asynctask-android">how在两个不同的数据类型传递给AsyncTask的，Android的

• What arguments are passed into AsyncTask<arg1, arg2, arg3>?
• Slidenerd Android AsyncTask Tutorial: Android Tutorial For Beginners
• Android: Why, When and How to use AsyncTask with example
• Understanding AsyncTask – Once and Forever
• Dealing with AsyncTask and Screen Orientation
• How to pass multiple parameters to AsynkTask
• how to pass in two different data types to AsyncTask, Android

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