android - Android AsyncTask示例和解释

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Using AsyncTask

(1个答案)


已关闭6年。




我想在我的应用程序中使用AsyncTask，但是在查找代码片段时遇到了麻烦，该代码片段仅提供了有关工作原理的简单说明。我只希望有一些东西可以帮助我快速恢复速度，而不必再次经历the documentation或很多问答。

最佳答案

AsyncTask是在Android中实现并行性的最简单方法之一，而无需处理诸如Threads之类的更复杂的方法。尽管它提供了与UI线程的基本并行度，但不应将其用于更长的操作(例如，不超过2秒)。

AsyncTask有四种方法

onPreExecute()

doInBackground()

onProgressUpdate()

onPostExecute()

doInBackground()最重要，因为它是执行后台计算的地方。

代码:

这是带有说明的骨骼代码概述:

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 parameter");
    }

    // 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
        }
    }
}

流程图:

这是一个图表，以帮助解释所有参数和类型的去向:



其他有用的链接:

What arguments are passed into AsyncTask<arg1, arg2, arg3>?

Slidenerd Android AsyncTask Tutorial: Android Tutorial For Beginners

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

关于android - Android AsyncTask示例和解释，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/25647881/