Android -从计时器线程更新位图

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.ImageView;
import androidx.appcompat.app.AppCompatActivity;

import java.util.Timer;
import java.util.TimerTask;

public class MainActivity extends AppCompatActivity {

    private ImageView imageView;
    private Bitmap bitmap;
    private Handler handler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            if (msg.what == 1) {
                imageView.setImageBitmap(bitmap);
            }
            return true;
        }
    });

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        imageView = findViewById(R.id.imageView);

        // 初始化位图
        bitmap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        canvas.drawColor(Color.BLUE);

        // 设置计时器
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new TimerTask() {
            int count = 0;
            @Override
            public void run() {
                // 在后台线程中更新位图
                Canvas canvas = new Canvas(bitmap);
                canvas.drawColor(Color.argb(255, count * 10, 255 - count * 10, 0));
                count++;

                // 发送消息到UI线程更新ImageView
                handler.sendEmptyMessage(1);
            }
        }, 0, 1000); // 每秒更新一次
    }
}

@Override
protected void onDestroy() {
    super.onDestroy();
    timer.cancel();
}