Handler详解

Handler使用详解

1. 简单实现

1.1 基础知识

• void handleMessage(Message msg); 处理消息的方法,通常是用于被重写!
• sendEmptyMessage(int what); 发送空消息
• sendEmptyMessageDelayed(int what,long delayMillis); 指定延时多少毫秒后发送空信息
• sendMessage(Message msg); 立即发送信息
• sendMessageDelayed(Message msg); 指定延时多少毫秒后发送信息
• final boolean hasMessage(int what); 检查消息队列中是否包含what属性为指定值的消息 如果是参数为(int what,Object object):除了判断what属性,还需要判断Object属性是否为指定对象的消息

1.2 计时器实战

1. 页面布局activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    tools:context=".MainActivity">
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="35dp"
        android:id="@+id/tv_test"/>

</LinearLayout>

2. 主页面MainActivity.java

public class MainActivity extends AppCompatActivity {

    private TextView tv_test;

    String test[] = new String[]{
            "1", "2", "3", "4", "5", "6", "7", "8", "9"
    };
    int numStart = 0;

    Handler handler = new Handler() {
        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);
            if (msg.what == 0x123) {
                tv_test.setText(test[numStart++%9]);
                Log.d("MainActivity", "numStart:" + numStart);
            }
        }
    };


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
        new Timer().schedule(new TimerTask() {
            @Override
            public void run() {
                handler.sendEmptyMessage(0x123);
            }
        },0,1000);
    }

    private void initView() {
        tv_test = (TextView) findViewById(R.id.tv_test);
    }
}