Android 中不用线程如何实现倒计时

需求：

有多个组件可以开启倒计时，正常情况下默认倒计时时间终了后更新UI，另，用户可以取消指定倒计时。

这里使用CountDownTimer进行倒计时，其中回调函数onFinish是在倒计时终了时回调，onTick是在倒计时开始时回调，用户可以使用CountDownTimer对象的cancel方法取消倒计时。

这样做的好处：不需要使用繁琐的线程去控制倒计时，更方便的进行UI更新。

上代码：

MainActivity

package test.demo.countdowntest;
import android.os.Bundle;
import android.os.CountDownTimer;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity implements View.OnClickListener{
  private Button bt1, bt2, bt3;
  private ProgressBar pb1, pb2, pb3;
  private MyCount mc1,mc2, mc3;
  private boolean mc1Click = false;
  private boolean mc2Click = false;
  private boolean mc3Click = false;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    bt1 = ((Button) findViewById(R.id.bt1));
    bt2 = ((Button) findViewById(R.id.bt2));
    bt3 = ((Button) findViewById(R.id.bt3));
    bt1.setonClickListener(this);
    bt2.setonClickListener(this);
    bt3.setonClickListener(this);
    pb1 = ((ProgressBar) findViewById(R.id.pb1));
    pb2 = ((ProgressBar) findViewById(R.id.pb2));
    pb3 = ((ProgressBar) findViewById(R.id.pb3));
    mc1 = new MyCount(30000, 1000);
    mc1.setPb(bt1, pb1);
    mc2 = new MyCount(30000, 1000);
    mc2.setPb(bt2, pb2);
    mc3 = new MyCount(30000, 1000);
    mc3.setPb(bt3, pb3);
  }
  @Override
  public void onClick(View view) {
    switch (view.getId()) {
      case R.id.bt1:
 if (mc1Click) {
   mc1.cancel();
   pb1.setVisibility(View.GONE);
   mc1Click = false;
 } else {
   pb1.setVisibility(View.VISIBLE);
   mc1.start();
   mc1Click = true;
 }
 break;
      case R.id.bt2:
 if (mc2Click) {
   pb2.setVisibility(View.GONE);
   mc2.cancel();
   mc2Click = false;
 } else {
   pb2.setVisibility(View.VISIBLE);
   mc2.start();
   mc2Click = true;
 }
 break;
      case R.id.bt3:
 if (mc3Click) {
   pb3.setVisibility(View.GONE);
   mc3.cancel();
   mc3Click = false;
 } else {
   pb3.setVisibility(View.VISIBLE);
   mc3.start();
   mc3Click = true;
 }
 break;
    }
  }
  
  class MyCount extends CountDownTimer {
    Button mBt;
    ProgressBar mPb;
    public MyCount(long millisInFuture, long countDownInterval) {
      super(millisInFuture, countDownInterval);
    }
    public void setPb(Button bt, ProgressBar pb) {
      mBt = bt;
      mPb = pb;
    }
    @Override
    public void onFinish() {
      mPb.setVisibility(View.GONE);
    }
    @Override
    public void onTick(long millisUntilFinished) {
      mBt.setText("请等待30秒(" + millisUntilFinished / 1000 + ")...");
      Toast.makeText(MainActivity.this, millisUntilFinished / 1000 + "", Toast.LENGTH_LONG).show();
    }
  }
}

activity_main.xml

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