Android 中的 Handler 消息处理

主要用途:

1. 未来某时做某事.
2. 线程间通信.

package com.example.hello;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;

import com.example.hello.util.ToastUtil;

public class HandlerActivity extends AppCompatActivity {
    
    

    private Handler handler;

    @SuppressLint("HandlerLeak")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_handler);
        handler = new Handler();
        // 3 秒后执行
        handler.postDelayed(() -> {
    
    
            Intent intent = new Intent(HandlerActivity.this, ButtonActivity.class);
            startActivity(intent);
        }, 3000);

        handler = new Handler() {
    
    
            @Override
            public void handleMessage(@NonNull Message msg) {
    
    
                super.handleMessage(msg);
                switch (msg.what) {
    
    
                    case 1:
                        ToastUtil.showShortToast(HandlerActivity.this, "1 线程通信成功");
                        break;
                    default:
                        throw new IllegalStateException("Unexpected value: " + msg.what);
                }
            }
        };

        new Thread() {
    
    
            @Override
            public void run() {
    
    
                super.run();
                Message message = new Message();
                message.what = 1;
                handler.sendMessage(message);
            }
        }.start();

    }
}