android利用handler实现倒计时功能

本文实例为大家分享了android利用handler实现倒计时的具体代码，供大家参考，具体内容如下

xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
tools:context=".MainActivity">

<TextView
 android:id="@+id/text"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="Hello World!"
 app:layout_constraintBottom_toBottomOf="parent"
 app:layout_constraintLeft_toLeftOf="parent"
 app:layout_constraintRight_toRightOf="parent"
 app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

java

package com.tcy.handlertest;

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

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.TextView;

import java.lang.ref.WeakReference;

public class MainActivity extends AppCompatActivity {

/**
 * 倒计时标记handler code
 */
public static final int COUNT_DOWN_CODE = 10001;
/**
 * 倒计时最大值
 */
public static final int MAX_COUNT = 10;
/**
 * 倒计时间隔
 */
public static final int DELAY_MILLIS = 1000;
TextView textView;

@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 textView = findViewById(R.id.text);

CountdownTimeHandler handler = new CountdownTimeHandler(this);
 Message message = Message.obtain();
 message.what = COUNT_DOWN_CODE;
 message.arg1 = MAX_COUNT;
 handler.sendMessageDelayed(message, DELAY_MILLIS);

}

public static class CountdownTimeHandler extends Handler {
 //弱引用加在上下文上面
 final WeakReference<MainActivity> weakReference;

//这个方法要改一下，这样就能直接传进来上下文
 public CountdownTimeHandler(MainActivity activity) {
  this.weakReference = new WeakReference<>(activity);
 }

@Override
 public void handleMessage(@NonNull Message msg) {
  super.handleMessage(msg);

//得到上下文
  MainActivity activity = weakReference.get();

switch (msg.what) {
   case COUNT_DOWN_CODE:
    int value = msg.arg1;
    activity.textView.setText(String.valueOf(value--));

if (value >= 0) {
     //再把value发出去
     Message message = Message.obtain();
     message.what = COUNT_DOWN_CODE;
     message.arg1 = value;
     sendMessageDelayed(message, DELAY_MILLIS);
    }

break;
  }
 }
}
}

来源：https://blog.csdn.net/melocarter/article/details/109991275