public class MainActivity extends Activity {

  private RelativeLayout countDown;
  // 倒計時
  private TextView daysTv, hoursTv, minutesTv, secondsTv;
  private long mDay = 10;
  private long mHour = 10;
  private long mMin = 30;
  private long mSecond = 00;// 天 ,小時,分鐘,秒
  private boolean isRun = true;
  private Handler timeHandler = new Handler() {

    @Override
    public void handleMessage(Message msg) {
      super.handleMessage(msg);
      if (msg.what==1) {
        computeTime();
        daysTv.setText(mDay+"");
        hoursTv.setText(mHour+"");
        minutesTv.setText(mMin+"");
        secondsTv.setText(mSecond+"");
        if (mDay==0&&mHour==0&&mMin==0&&mSecond==0) {
          countDown.setVisibility(View.GONE);
        }
      }
    }
  };

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

    countDown = (RelativeLayout) findViewById(R.id.countdown_layout);
    daysTv = (TextView) findViewById(R.id.days_tv);
    hoursTv = (TextView) findViewById(R.id.hours_tv);
    minutesTv = (TextView) findViewById(R.id.minutes_tv);
    secondsTv = (TextView) findViewById(R.id.seconds_tv);

    startRun();
  }

  /**
   * 開啟倒計時
   */
  private void startRun() {
    new Thread(new Runnable() {

      @Override
      public void run() {
        // TODO Auto-generated method stub
        while (isRun) {
          try {
            Thread.sleep(1000); // sleep 1000ms
            Message message = Message.obtain();
            message.what = 1;
            timeHandler.sendMessage(message);
          } catch (Exception e) {
            e.printStackTrace();
          }
        }
      }
    }).start();
  }

  /**
   * 倒計時計算
   */
  private void computeTime() {
    mSecond--;
    if (mSecond < 0) {
      mMin--;
      mSecond = 59;
      if (mMin < 0) {
        mMin = 59;
        mHour--;
        if (mHour < 0) {
          // 倒計時結束
          mHour = 23;
          mDay--;
        }
      }
    }
  }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:id="@+id/countdown_layout"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:background="@android:color/white"
  android:gravity="center" >

  <RelativeLayout
    android:id="@+id/daojishi_rl"
    android:layout_width="match_parent"
    android:layout_height="40.0dip"
    android:layout_marginLeft="10.0dip"
    android:layout_marginRight="10.0dip"
    android:gravity="center" >

    <ImageView
      android:id="@+id/describe_iv"
      android:layout_width="40.0dip"
      android:layout_height="40.0dip"
      android:background="@drawable/clock"
      android:gravity="center_vertical" />

    <TextView
      android:id="@+id/describe_tv"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerVertical="true"
      android:layout_marginRight="5.0dip"
      android:layout_toRightOf="@+id/describe_iv"
      android:text="距離活動還有 "
      android:textSize="25sp" />

    <TextView
      android:id="@+id/days_tv"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerVertical="true"
      android:layout_toRightOf="@+id/describe_tv"
      android:textColor="@color/colorAccent"
      android:gravity="center"
      android:text="20"
      android:textSize="20sp" />

    <TextView
      android:id="@+id/colon0"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerVertical="true"
      android:layout_marginLeft="5.0dip"
      android:layout_marginRight="3.0dip"
      android:layout_toRightOf="@+id/days_tv"
      android:text="天"
      android:textSize="20sp"
      android:textStyle="bold" />
  </RelativeLayout>

  <RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/daojishi_rl"
    android:gravity="center_horizontal" >

    <TextView
      android:id="@+id/hours_tv"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerVertical="true"
      android:layout_toLeftOf="@+id/colon1"
      android:textColor="@color/colorAccent"
      android:gravity="center"
      android:text="23"
      android:textSize="20sp" />

    <TextView
      android:id="@+id/colon1"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerVertical="true"
      android:layout_marginLeft="3.0dip"
      android:layout_marginRight="3.0dip"
      android:layout_toLeftOf="@+id/minutes_tv"
      android:text=":"
      android:textSize="20sp"
      android:textStyle="bold" />

    <TextView
      android:id="@+id/minutes_tv"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerVertical="true"
      android:layout_toLeftOf="@+id/colon2"
      android:textColor="@color/colorAccent"
      android:gravity="center"
      android:text="59"
      android:textSize="20sp" />

    <TextView
      android:id="@+id/colon2"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerVertical="true"
      android:layout_marginLeft="3.0dip"
      android:layout_marginRight="3.0dip"
      android:layout_toLeftOf="@+id/seconds_tv"
      android:text=":"
      android:textSize="20sp"
      android:textStyle="bold" />

    <TextView
      android:id="@+id/seconds_tv"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignParentRight="true"
      android:layout_centerVertical="true"
      android:gravity="center"
      android:text="59"
      android:textColor="@color/colorAccent"
      android:textSize="20sp" />
  </RelativeLayout>

</RelativeLayout>