AsyncTask API 在 Android 中被弃用 11. 有哪些替代方案？

Question

Google 在 Android 11 中弃用 Android AsyncTask API 并建议改用 java.util.concurrent。你可以查看提交 here

 *
 * @deprecated Use the standard <code>java.util.concurrent</code> or
 *   <a href="https://developer.android.com/topic/libraries/architecture/coroutines">
 *   Kotlin concurrency utilities</a> instead.
 */
@Deprecated
public abstract class AsyncTask<Params, Progress, Result> {

如果您在 Android 中维护带有异步任务的旧代码库，您将来可能不得不更改它。我的问题是应该使用 java.util.concurrent 正确替换下面显示的代码片段。它是 Activity 的静态内部 class。我正在寻找可以与 minSdkVersion 16

一起使用的东西

private static class LongRunningTask extends AsyncTask<String, Void, MyPojo> {
        private static final String TAG = MyActivity.LongRunningTask.class.getSimpleName();
        private WeakReference<MyActivity> activityReference;

        LongRunningTask(MyActivity context) {
            activityReference = new WeakReference<>(context);
        }

        @Override
        protected MyPojo doInBackground(String... params) {
            // Some long running task
            
        }

        @Override
        protected void onPostExecute(MyPojo data) {

            MyActivity activity = activityReference.get();
            activity.progressBar.setVisibility(View.GONE);
            populateData(activity, data) ;
        }     


    }

Answer 1

private WeakReference<MyActivity> activityReference;

很高兴它已被弃用，because the WeakReference<Context> was always a hack, and not a proper solution。

现在人们将有机会净化他们的代码。

AsyncTask<String, Void, MyPojo>

基于这段代码，其实不需要Progress，还有一个String输入+MyPojo输出。

这实际上很容易完成，无需使用任何 AsyncTask。

public class TaskRunner {
    private final Executor executor = Executors.newSingleThreadExecutor(); // change according to your requirements
    private final Handler handler = new Handler(Looper.getMainLooper());

    public interface Callback<R> {
        void onComplete(R result);
    }

    public <R> void executeAsync(Callable<R> callable, Callback<R> callback) {
        executor.execute(() -> {
            final R result = callable.call();
            handler.post(() -> {
                callback.onComplete(result);
            });
        });
    }
}

如何传入String？像这样：

class LongRunningTask implements Callable<MyPojo> {
    private final String input;

    public LongRunningTask(String input) {
        this.input = input;
    }

    @Override
    public MyPojo call() {
        // Some long running task
        return myPojo;
    }
}

和

// in ViewModel
taskRunner.executeAsync(new LongRunningTask(input), (data) -> {
    // MyActivity activity = activityReference.get();
    // activity.progressBar.setVisibility(View.GONE);
    // populateData(activity, data) ;

    loadingLiveData.setValue(false);
    dataLiveData.setValue(data);
});

// in Activity
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main_activity);

    viewModel = ViewModelProviders.of(this).get(MyViewModel.class);
    viewModel.loadingLiveData.observe(this, (loading) -> {
        if(loading) {
            progressBar.setVisibility(View.VISIBLE);
        } else {
            progressBar.setVisibility(View.GONE);
        }
    });

    viewModel.dataLiveData.observe(this, (data) -> {
        populateData(data);
    }); 
}

这个例子使用了一个单线程池，适合数据库写入（或序列化网络请求），但如果你想要数据库读取或多个请求的东西，你可以考虑以下执行器配置：

private static final Executor THREAD_POOL_EXECUTOR =
        new ThreadPoolExecutor(5, 128, 1,
                TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());

Answer 2

Google 建议使用 Java 的并发框架或 Kotlin Coroutines。但是 Rxjava 最终具有比 java 并发性更多的灵活性和特性，因此获得了相当多的人气。

Answer 3

Android 在 Android 11 中弃用了 ~~AsyncTask~~ API 以摆脱一部分问题。

那么，现在怎么样了？

线程
执行者
RxJava
可听期货
协程

为什么要协程？

Coroutines are the Kotlin way to do asynchronous programming. Compiler support is stable since Kotlin 1.3, together with a kotlinx.coroutines library -

结构化并发
非阻塞，顺序代码
取消传播
自然异常处理

Answer 4

按照Android documentation AsyncTask was deprecated in API level 30 and it is suggested to use the standard java.util.concurrent or Kotlin concurrency utilities代替。

使用后者可以非常简单地实现：

在 CoroutineScope 上创建通用扩展函数:

 fun <R> CoroutineScope.executeAsyncTask(
         onPreExecute: () -> Unit,
         doInBackground: () -> R,
         onPostExecute: (R) -> Unit
 ) = launch {
     onPreExecute() // runs in Main Thread
     val result = withContext(Dispatchers.IO) { 
         doInBackground() // runs in background thread without blocking the Main Thread
     }
     onPostExecute(result) // runs in Main Thread
 }

将函数与具有 Dispatchers.Main 上下文的任何 CoroutineScope 一起使用：

在ViewModel:

class MyViewModel : ViewModel() {

    fun someFun() {
        viewModelScope.executeAsyncTask(onPreExecute = {
            // ... runs in Main Thread
        }, doInBackground = {
            // ... runs in Worker(Background) Thread
            "Result" // send data to "onPostExecute"
        }, onPostExecute = {
            // runs in Main Thread
            // ... here "it" is the data returned from "doInBackground"
        })
    }
}

在Activity或Fragment中：

lifecycleScope.executeAsyncTask(onPreExecute = {
    // ... runs in Main Thread
}, doInBackground = {
    // ... runs in Worker(Background) Thread
    "Result" // send data to "onPostExecute"
}, onPostExecute = {
    // runs in Main Thread
    // ... here "it" is the data returned from "doInBackground"
})

要使用 viewModelScope 或 lifecycleScope 将下一行添加到应用程序的 build.gradle 文件的依赖项中：

implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$LIFECYCLE_VERSION" // for viewModelScope
implementation "androidx.lifecycle:lifecycle-runtime-ktx:$LIFECYCLE_VERSION" // for lifecycleScope

撰写本文时 final LIFECYCLE_VERSION = "2.3.0-alpha05"

更新:

我们也可以使用onProgressUpdate函数实现进度更新：

fun <P, R> CoroutineScope.executeAsyncTask(
        onPreExecute: () -> Unit,
        doInBackground: suspend (suspend (P) -> Unit) -> R,
        onPostExecute: (R) -> Unit,
        onProgressUpdate: (P) -> Unit
) = launch {
    onPreExecute()

    val result = withContext(Dispatchers.IO) {
        doInBackground {
            withContext(Dispatchers.Main) { onProgressUpdate(it) }
        }
    }
    onPostExecute(result)
}

使用任何 CoroutineScope（viewModelScope/lifecycleScope，见上面的实现）和 Dispatchers.Main 我们可以调用它的上下文：

someScope.executeAsyncTask(
    onPreExecute = {
        // ... runs in Main Thread
    }, doInBackground = { publishProgress: suspend (progress: Int) -> Unit ->
        
        // ... runs in Background Thread

        // simulate progress update
        publishProgress(50) // call `publishProgress` to update progress, `onProgressUpdate` will be called
        delay(1000)
        publishProgress(100)

        
        "Result" // send data to "onPostExecute"
    }, onPostExecute = {
        // runs in Main Thread
        // ... here "it" is a data returned from "doInBackground"
    }, onProgressUpdate = {
        // runs in Main Thread
        // ... here "it" contains progress
    }
)

Answer 5

在这里，我使用协程为 AsyncTask 创建了一个替代方案，它可以与 AsyncTask 一样使用，而无需更改项目中的很多代码库。

创建一个新的抽象class AsyncTaskCoroutine 接受输入参数和输出参数数据类型of-course这些参数是可选的:)

 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.GlobalScope
 import kotlinx.coroutines.async
 import kotlinx.coroutines.launch

 abstract class AsyncTaskCoroutine<I, O> {
     var result: O? = null
     //private var result: O
     open fun onPreExecute() {}

     open fun onPostExecute(result: O?) {}
     abstract fun doInBackground(vararg params: I): O

     fun <T> execute(vararg input: I) {
         GlobalScope.launch(Dispatchers.Main) {
             onPreExecute()
             callAsync(*input)
         }
     }

     private suspend fun callAsync(vararg input: I) {
         GlobalScope.async(Dispatchers.IO) {
             result = doInBackground(*input)
         }.await()
         GlobalScope.launch(Dispatchers.Main) {

             onPostExecute(result)


         }
     }
 }

2。在 Activity 中，现在将其与旧的 AsycnTask 一样使用

 new AsyncTaskCoroutine() {
                @Override
                public Object doInBackground(Object[] params) {
                    return null;
                }
    
                @Override
                public void onPostExecute(@Nullable Object result) {
    
                }
    
                @Override
                public void onPreExecute() {
    
                }
            }.execute();

万一你需要发送传递参数

  new AsyncTaskCoroutine<Integer, Boolean>() {

     @Override
     public Boolean doInBackground(Integer... params) {
         return null;
     }

     @Override
     public void onPostExecute(@Nullable Boolean result) {

     }

     @Override
     public void onPreExecute() {

     }
 }.execute();

Answer 6

我的自定义替换：https://github.com/JohnyDaDeveloper/AndroidAsync

它仅在应用运行（更具体地说是计划任务的 activity 时有效），但它能够在后台任务完成后更新 UI

编辑：我的 AsyncTask 不再需要 Activiy 才能运行。

Answer 7

最简单的替代方法之一是使用 Thread

new Thread(new Runnable() {
    @Override
    public void run() {
        // do your stuff
        runOnUiThread(new Runnable() {
            public void run() {
                // do onPostExecute stuff
            }
        });
    }
}).start();

如果你的项目支持JAVA8，你可以使用lambda:

new Thread(() -> {
    // do background stuff here
    runOnUiThread(()->{
        // OnPostExecute stuff here
    });
}).start();

Answer 8

您可以使用此自定义 class 作为 AsyncTask<> 的替代方案，这与 AsyncTask 相同，因此您无需为此付出额外的努力。

import android.os.Handler;
import android.os.Looper;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class TaskRunner {

    private static final int CORE_THREADS = 3;
    private static final long KEEP_ALIVE_SECONDS = 60L;
    private static TaskRunner taskRunner = null;
    private Handler handler = new Handler(Looper.getMainLooper());
    private ThreadPoolExecutor executor;

    private TaskRunner() {
        executor = newThreadPoolExecutor();
    }

    public static TaskRunner getInstance() {
        if (taskRunner == null) {
            taskRunner = new TaskRunner();
        }
        return taskRunner;
    }

    public void shutdownService() {
        if (executor != null) {
            executor.shutdown();
        }
    }

    public void execute(Runnable command) {
        executor.execute(command);
    }

    public ExecutorService getExecutor() {
        return executor;
    }

    public <R> void executeCallable(@NonNull Callable<R> callable, @NonNull OnCompletedCallback<R> callback) {
        executor.execute(() -> {
            R result = null;
            try {
                result = callable.call();
            } catch (Exception e) {
                e.printStackTrace(); // log this exception
            } finally {
                final R finalResult = result;
                handler.post(() -> callback.onComplete(finalResult));
            }
        });
    }

    private ThreadPoolExecutor newThreadPoolExecutor() {
        return new ThreadPoolExecutor(
                CORE_THREADS,
                Integer.MAX_VALUE,
                KEEP_ALIVE_SECONDS,
                TimeUnit.SECONDS,
                new SynchronousQueue<>()
        );
    }

    public interface OnCompletedCallback<R> {
        void onComplete(@Nullable R result);
    }
}

如何使用？请按照以下示例进行操作。

使用 lambda 表达式

TaskRunner.getInstance().executeCallable(() -> 1, result -> {
});


TaskRunner.getInstance().execute(() -> {
});

没有 lambda 表达式

TaskRunner.getInstance().executeCallable(new Callable<Integer>() {
    @Override
    public Integer call() throws Exception {
        return 1;
    }
}, new TaskRunner.OnCompletedCallback<Integer>() {
    @Override
    public void onComplete(@Nullable Integer result) {

    }
});

TaskRunner.getInstance().execute(new Runnable() {
    @Override
    public void run() {

    }
});

注意：不要忘记关闭执行程序服务

TaskRunner.getInstance().shutdownService();

Answer 9

就把整个class换成这个Thread，放在一个方法里传变量

new Thread(() -> {
            // do background stuff here
            runOnUiThread(()->{
                // OnPostExecute stuff here
              
            });
        }).start();

并在 Fragment 中将上下文添加到 runOnUiThread() 方法：

 new Thread(() -> {
            // do background stuff here
            context.runOnUiThread(()->{
                // OnPostExecute stuff here
            });
        }).start();

Answer 10

您可以直接使用 java.util.concurrent 包中的 Executors。

我也搜索了一下，在这个 Android Async API is Deprecated post.

中找到了解决方案

不幸的是，post 使用的是 Kotlin，但经过一些努力我将其转换为 Java。所以这是解决方案。

ExecutorService executor = Executors.newSingleThreadExecutor();
Handler handler = new Handler(Looper.getMainLooper());

executor.execute(new Runnable() {
    @Override
    public void run() {

        //Background work here

        handler.post(new Runnable() {
            @Override
            public void run() {
                //UI Thread work here
            }
        });
    }
});

很简单吧？如果您在项目中使用 Java 8，则可以进一步简化它。

ExecutorService executor = Executors.newSingleThreadExecutor();
Handler handler = new Handler(Looper.getMainLooper());

executor.execute(() -> {
    //Background work here
    handler.post(() -> {
        //UI Thread work here
    });
});

虽然在代码的简洁性上还是比不上kotlin，但是比之前的java版本要好。

希望这对您有所帮助。谢谢

Answer 11

使用此 class 在后台线程中执行后台任务此 class 适用于所有 android API 版本包括 Android 11 此代码也与 AsyncTask 和 doInBackground 和 onPostExecute 方法相同

public abstract class BackgroundTask {

    private Activity activity;
    public BackgroundTask(Activity activity) {
        this.activity = activity;
    }

    private void startBackground() {
        new Thread(new Runnable() {
            public void run() {

                doInBackground();
                activity.runOnUiThread(new Runnable() {
                    public void run() {

                        onPostExecute();
                    }
                });
            }
        }).start();
    }
    public void execute(){
        startBackground();
    }

    public abstract void doInBackground();
    public abstract void onPostExecute();

}

复制上面的class后，你就可以用这个了：

new BackgroundTask(MainActivity.this) {
        @Override
        public void doInBackground() {

            //put you background code
            //same like doingBackground
            //Background Thread
        }

        @Override
        public void onPostExecute() {

            //hear is result part same
            //same like post execute
            //UI Thread(update your UI widget)
        }
    }.execute();

Answer 12

HandlerThread 可以替代 AsyncTask。它们是 long-运行ning 线程。 HandlerThread 的示例如下：

您可以创建两个处理程序对象。其中之一将用于将消息从 workerThread 发送到 UI Thread.

Handler uiHandler,workerHandler;
Message msg;
HandlerThread handlerThread = new HandlerThread("MyHandlerThread");
handlerThread.start();
Handler.Callback callback=new Handler.Callback() {
        @Override
        public boolean handleMessage(@NonNull Message msg) {
            // handle messages sent from working thread (like updating UI)...
            return true;
        }
    }
uiHandler=new Handler(callback);
workerHandler = new Handler(handlerThread.getLooper());
workerHandler.post(new Runnable(){
           // Perform required task
           uiHandler.sendMessage(msg); // this message will be sent to and handled by UI Thread
});

此外，请记住 HandlerThreads 运行在 activity 的生命周期之外，因此需要正确清理它们，否则会出现线程泄漏。您可以在 Activity 的 onDestroy() 中使用 quit() 或 quitSafely() 方法来防止线程泄漏。

Answer 13

您可以根据需要迁移到下一个方法

线程 + 处理程序
执行者
未来
意图服务
JobScheduler
RxJava
协程 (Kotlin)

[Android async variants]

Answer 14

我实际上写了两个关于它的 Medium 故事：

第一个是 Java 和 Runnable 的解决方法，第二个是 Kotlin 和协程解决方案。当然，两者都带有代码示例。

Answer 15

这是我的代码

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public abstract class AsyncTaskRunner<T> {

    private ExecutorService executorService = null;
    private Set<Callable<T>> tasks = new HashSet<>();

    public AsyncTaskRunner() {
        this.executorService = Executors.newSingleThreadExecutor();
    }
    
    public AsyncTaskRunner(int threadNum) {
        this.executorService = Executors.newFixedThreadPool(threadNum);
    }


    public void addTask(Callable<T> task) {
        tasks.add(task);
    }

    public void execute() {
        try {
            List<Future<T>> features = executorService.invokeAll(tasks);

            List<T> results = new ArrayList<>();
            for (Future<T> feature : features) {
                results.add(feature.get());
            }
            this.onPostExecute(results);
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
            this.onCancelled();
        } finally {
            executorService.shutdown();
        }

    }

    protected abstract void onPostExecute(List<T> results);

    protected void onCancelled() {
        // stub
    }

}

和用法示例。扩展 AsyncTaskRunner class,

class AsyncCalc extends AsyncTaskRunner<Integer> {

    public void addRequest(final Integer int1, final Integer int2) {
        this.addTask(new Callable<Integer>() {
            @Override
            public Integer call() throws Exception {
                // Do something in background
                return int1 + int2;
            }
        });
    }

    @Override
    protected void onPostExecute(List<Integer> results) {
        for (Integer answer: results) {
            Log.d("AsyncCalc", answer.toString());
        }
    }
}

那就用吧！

AsyncCalc calc = new AsyncCalc();
calc.addRequest(1, 2);
calc.addRequest(2, 3);
calc.addRequest(3, 4);
calc.execute();

Answer 16

接受的答案很好。但... 我没有看到 cancel() 方法实现

所以我的实现有可能取消运行ning 任务（模拟取消）如下。在任务中断的情况下，需要取消而不是运行 postExecute() 方法。

public abstract class AsyncTaskExecutor<Params> {
    public static final String TAG = "AsyncTaskRunner";

    private static final Executor THREAD_POOL_EXECUTOR =
            new ThreadPoolExecutor(5, 128, 1,
                    TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());

    private final Handler mHandler = new Handler(Looper.getMainLooper());
    private boolean mIsInterrupted = false;

    protected void onPreExecute(){}
    protected abstract Void doInBackground(Params... params);
    protected void onPostExecute(){}
    protected void onCancelled() {}

    @SafeVarargs
    public final void executeAsync(Params... params) {
        THREAD_POOL_EXECUTOR.execute(() -> {
            try {
                checkInterrupted();
                mHandler.post(this::onPreExecute);

                checkInterrupted();
                doInBackground(params);

                checkInterrupted();
                mHandler.post(this::onPostExecute);
            } catch (InterruptedException ex) {
                mHandler.post(this::onCancelled);
            } catch (Exception ex) {
                Log.e(TAG, "executeAsync: " + ex.getMessage() + "\n" + Debug.getStackTrace(ex));
            }
        });
    }

    private void checkInterrupted() throws InterruptedException {
        if (isInterrupted()){
            throw new InterruptedException();
        }
    }

    public void cancel(boolean mayInterruptIfRunning){
        setInterrupted(mayInterruptIfRunning);
    }

    public boolean isInterrupted() {
        return mIsInterrupted;
    }

    public void setInterrupted(boolean interrupted) {
        mIsInterrupted = interrupted;
    }
}

使用此 class 的示例：

public class MySearchTask extends AsyncTaskExecutor<String> {

    public MySearchTask(){
    }

    @Override
    protected Void doInBackground(String... params) {
        // Your long running task
        return null;
    }

    @Override
    protected void onPostExecute() {
        // update UI on task completed
    }

    @Override
    protected void onCancelled() {
        // update UI on task cancelled
    }
}

MySearchTask searchTask = new MySearchTask();
searchTask.executeAsync("Test");

Answer 17

在这里，我还使用抽象 class 创建了 AsyncTask 的替代方案，它可以直接复制为 class。

/app/src/main/java/../AsyncTasks.java

public abstract class AsyncTasks {
    private final ExecutorService executors;

    public AsyncTasks() {
        this.executors = Executors.newSingleThreadExecutor();
    }

    private void startBackground() {
        onPreExecute();
        executors.execute(new Runnable() {
            @Override
            public void run() {
                doInBackground();
                new Handler(Looper.getMainLooper()).post(new Runnable() {
                    @Override
                    public void run() {
                        onPostExecute();
                    }
                });
            }
        });
    }

    public void execute() {
        startBackground();
    }

    public void shutdown() {
        executors.shutdown();
    }

    public boolean isShutdown() {
        return executors.isShutdown();
    }

    public abstract void onPreExecute();

    public abstract void doInBackground();

    public abstract void onPostExecute();
}

上面的实现/使用class

new AsyncTasks() {
     @Override
            public void onPreExecute() { 
             // before execution
      }

     @Override
            public void doInBackground() {
              // background task here 
            }

     @Override
            public void onPostExecute() { 
             // Ui task here
            }
     }.execute();

AsyncTask API 在 Android 中被弃用 11. 有哪些替代方案？

The AsyncTask API is deprecated in Android 11. What are the alternatives?

java

android

android-asynctask

kotlin

kotlin-coroutines

那么，现在怎么样了？

为什么要协程？