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java - Handler(Handler.Callback) 已弃用

问题描述

Handler(android.os.Handler.Callback) 已弃用，我应该改用什么？

Handler handler = new Handler(new Handler.Callback() {
    @Override
    public boolean handleMessage(@NonNull Message message) {
        switch(message.what) {
            case READ_MESSAGE:
                byte[] readBuff = (byte[]) message.obj;
                String tempMessage = new String(readBuff, 0, message.arg1);
                readMsg.setText(tempMessage);
                break;
        }
        return true;
    }
});

标签： javaandroidandroid-handler

解决方案

从 API 级别 30 开始，有 2 个构造函数被弃用。

谷歌解释了下面的原因。

在 Handler 构造期间隐式选择 Looper 可能会导致操作丢失（如果 Handler 不期待新任务并退出）、崩溃（如果有时在没有 Looper 活动的线程上创建处理程序）或竞争条件的错误，与处理程序关联的线程不是作者预期的。相反，使用 Executor 或显式指定 Looper，使用 Looper#getMainLooper、{link android.view.View#getHandler} 或类似方法。如果为了兼容性需要隐式线程本地行为，请使用 new Handler(Looper.myLooper(), callback) 让读者清楚。

解决方案 1：使用Executor

1.在主线程中执行代码。

// Create an executor that executes tasks in the main thread. 
Executor mainExecutor = ContextCompat.getMainExecutor(this);

// Execute a task in the main thread
mainExecutor.execute(new Runnable() {
    @Override
    public void run() {
        // You code logic goes here.
    }
});

2.在后台线程中执行代码

// Create an executor that executes tasks in a background thread.
ScheduledExecutorService backgroundExecutor = Executors.newSingleThreadScheduledExecutor();

// Execute a task in the background thread.
backgroundExecutor.execute(new Runnable() {
    @Override
    public void run() {
        // Your code logic goes here.
    }
});

// Execute a task in the background thread after 1 second.
backgroundExecutor.schedule(new Runnable() {
    @Override
    public void run() {
        // Your code logic goes here
    }
}, 1, TimeUnit.SECONDS);

注意：使用后记得关闭执行器。

backgroundExecutor.shutdown(); // or backgroundExecutor.shutdownNow();

3.在后台线程执行代码，在主线程更新UI。

// Create an executor that executes tasks in the main thread. 
Executor mainExecutor = ContextCompat.getMainExecutor(this);

// Create an executor that executes tasks in a background thread.
ScheduledExecutorService backgroundExecutor = Executors.newSingleThreadScheduledExecutor();

// Execute a task in the background thread.
backgroundExecutor.execute(new Runnable() {
    @Override
    public void run() {
        // Your code logic goes here.
        
        // Update UI on the main thread
        mainExecutor.execute(new Runnable() {
            @Override
            public void run() {
                // You code logic goes here.
            }
        });
    }
});

解决方案 2：使用以下构造函数之一显式指定 Looper。

1.在主线程中执行代码

1.1。带有 Looper 的处理程序

Handler mainHandler = new Handler(Looper.getMainLooper());

1.2带有 Looper 和 Handler.Callback 的 Handler

Handler mainHandler = new Handler(Looper.getMainLooper(), new Handler.Callback() {
    @Override
    public boolean handleMessage(@NonNull Message message) {
        // Your code logic goes here.
        return true;
    }
});

2.在后台线程中执行代码

2.1。带有 Looper 的处理程序

// Create a background thread that has a Looper
HandlerThread handlerThread = new HandlerThread("HandlerThread");
handlerThread.start();

// Create a handler to execute tasks in the background thread.
Handler backgroundHandler = new Handler(handlerThread.getLooper());

2.2. 带有 Looper 和 Handler.Callback 的处理程序

// Create a background thread that has a Looper
HandlerThread handlerThread = new HandlerThread("HandlerThread");
handlerThread.start();

// Create a handler to execute taks in the background thread.
Handler backgroundHandler = new Handler(handlerThread.getLooper(), new Handler.Callback() {
    @Override
    public boolean handleMessage(@NonNull Message message) {
        // Your code logic goes here.
        return true;
    }
});

注意：使用后记得松开线。

handlerThread.quit(); // or handlerThread.quitSafely();

3.在后台线程执行代码，在主线程更新UI。

// Create a handler to execute code in the main thread
Handler mainHandler = new Handler(Looper.getMainLooper());

// Create a background thread that has a Looper
HandlerThread handlerThread = new HandlerThread("HandlerThread");
handlerThread.start();

// Create a handler to execute in the background thread
Handler backgroundHandler = new Handler(handlerThread.getLooper(), new Handler.Callback() {
    @Override
    public boolean handleMessage(@NonNull Message message) {
        // Your code logic goes here.
        
        // Update UI on the main thread.
        mainHandler.post(new Runnable() {
            @Override
            public void run() {
                
            }
        });
        
        return true;
    }
});

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