// 在主線程創(chuàng)建Handler會自動關(guān)聯(lián)主線程的Looper
Handler mainHandler = new Handler(Looper.getMainLooper()) {
    @Override
    public void handleMessage(Message msg) {
        // 處理消息
        switch (msg.what) {
            case 1:
                String text = (String) msg.obj;
                textView.setText(text);
                break;
        }
    }
};

// 發(fā)送空消息
handler.sendEmptyMessage(1);
// 發(fā)送帶what的消息
Message msg = handler.obtainMessage();
msg.what = 2;
msg.obj = "Hello Handler";
handler.sendMessage(msg);
// 延遲發(fā)送
handler.sendEmptyMessageDelayed(1, 1000); // 1秒后發(fā)送
handler.sendMessageDelayed(msg, 2000); // 2秒后發(fā)送

new Thread(() -> {
    // 為當(dāng)前線程創(chuàng)建Looper
    Looper.prepare();
    Handler threadHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            // 處理子線程消息
        }
    };
    // 開始消息循環(huán)
    Looper.loop();
}).start();

new Thread(() -> {
    // 模擬耗時操作
    try {
        Thread.sleep(1000);
        // 通過Handler發(fā)送消息到主線程更新UI
        Message msg = mainHandler.obtainMessage();
        msg.what = 1;
        msg.obj = "更新后的文本";
        mainHandler.sendMessage(msg);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}).start();

// 延遲執(zhí)行
handler.postDelayed(() -> {
    Toast.makeText(this, "5秒后執(zhí)行", Toast.LENGTH_SHORT).show();
}, 5000);
// 循環(huán)執(zhí)行
final Runnable runnable = new Runnable() {
    @Override
    public void run() {
        // 執(zhí)行任務(wù)
        Log.d("Handler", "每隔1秒執(zhí)行");
        // 再次post實(shí)現(xiàn)循環(huán)
        handler.postDelayed(this, 1000);
    }
};
handler.postDelayed(runnable, 1000);
// 取消定時任務(wù)
handler.removeCallbacks(runnable);

// 工作線程
class WorkerThread extends Thread {
    public Handler workerHandler;
    @Override
    public void run() {
        Looper.prepare();
        workerHandler = new Handler(Looper.myLooper()) {
            @Override
            public void handleMessage(Message msg) {
                // 處理來自主線程的消息
                String task = (String) msg.obj;
                Log.d("WorkerThread", "執(zhí)行任務(wù): " + task);
                // 可以回傳結(jié)果給主線程
                Message resultMsg = mainHandler.obtainMessage();
                resultMsg.what = 2;
                resultMsg.obj = task + " 完成";
                mainHandler.sendMessage(resultMsg);
            }
        };
        Looper.loop();
    }
}
// 主線程發(fā)送任務(wù)給工作線程
WorkerThread worker = new WorkerThread();
worker.start();
// 等待workerHandler初始化
new Handler().postDelayed(() -> {
    if (worker.workerHandler != null) {
        Message msg = worker.workerHandler.obtainMessage();
        msg.obj = "下載文件";
        worker.workerHandler.sendMessage(msg);
    }
}, 1000);

// 創(chuàng)建HandlerThread
HandlerThread handlerThread = new HandlerThread("MyHandlerThread");
handlerThread.start();
// 獲取HandlerThread的Looper創(chuàng)建Handler
Handler threadHandler = new Handler(handlerThread.getLooper()) {
    @Override
    public void handleMessage(Message msg) {
        // 在后臺線程處理消息
    }
};
// 發(fā)送消息
threadHandler.post(() -> {
    // 在HandlerThread中執(zhí)行
});
// 退出時釋放資源
handlerThread.quitSafely();

// 使用靜態(tài)內(nèi)部類+弱引用
private static class SafeHandler extends Handler {
    private final WeakReference<Activity> activityRef;
    public SafeHandler(Activity activity) {
        super(Looper.getMainLooper());
        this.activityRef = new WeakReference<>(activity);
    }
    @Override
    public void handleMessage(Message msg) {
        Activity activity = activityRef.get();
        if (activity != null && !activity.isFinishing()) {
            // 安全處理消息
        }
    }
}
// 在Activity中使用
private SafeHandler safeHandler = new SafeHandler(this);

// 復(fù)用Message對象（推薦）
Message msg = handler.obtainMessage(WHAT_ARG, obj);
handler.sendMessage(msg);
// 設(shè)置回調(diào)代替繼承Handler
handler.sendMessage(Message.obtain(handler, () -> {
    // 回調(diào)處理
}));

@Override
protected void onDestroy() {
    super.onDestroy();
    handler.removeCallbacksAndMessages(null);
    if (handlerThread != null) {
        handlerThread.quitSafely();
    }
}