在api级别30中，有2个构造函数已被弃用。
处理程序（）
处理程序（handler.callback）
谷歌解释了以下原因。
在处理程序构造期间隐式地选择一个循环器可能会导致错误，其中操作会自动丢失（如果处理程序不需要新任务并退出）、崩溃（如果处理程序有时是在没有活动循环器的线程上创建的）或争用条件，其中处理程序关联的线程不是作者预期的。相反，使用执行器或显式指定循环器，使用looper#getmainlooper、{link android.view.view#gethandler}或类似的方法。如果兼容性需要隐式线程本地行为，请使用新处理程序（looper.mylooper（），callback）向读者说明。
解决方案1：使用执行器
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：使用后请记住关闭执行器。

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

3.在后台线程中执行代码，并在主线程上更新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循环器。
处理程序（活套）
处理程序（looper，handler.callback）
1.在主线程中执行代码
1.1. 带活套的处理器

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

1.2带循环器和handler.callback的处理程序

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. 带活套的处理器

// 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. 带有循环器和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：使用后记得松开螺纹。

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

3.在后台线程中执行代码，并在主线程上更新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;
    }
});