1、實現效果
如下圖所示:
2、代碼實現
新建一個名爲CountdownTime
的項目,activity_main.xml
代碼如下:
<?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:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="@+id/countdownTimeTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="@string/maxTime"
android:textSize="60sp" />
</RelativeLayout>
MainActivity.class
代碼如下:
public class MainActivity extends AppCompatActivity {
/**
* 倒計時標記
*/
public static final int COUNTDOWN_TIME_CODE = 99999;
/**
* 倒計時間隔
*/
public static final int DELAY_MILLIS = 1000;
/**
* 倒計時最大值
*/
public static final int MAX_COUNT = 10;
/**
* 文本控件
*/
private TextView countdownTimeTextView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//初始化文本控件
countdownTimeTextView = findViewById(R.id.countdownTimeTextView);
//創建一個handler
CountdownTimeHandler handler = new CountdownTimeHandler(this);
//新建一個message
Message message = Message.obtain();
message.what = COUNTDOWN_TIME_CODE;
message.arg1 = MAX_COUNT;
//第一次發送message
handler.sendMessageDelayed(message, DELAY_MILLIS);
}
public static class CountdownTimeHandler extends Handler {
/**
* 倒計時最小值
*/
public static final int MIN_COUNT = 0;
//創建MainActivity弱引用
final WeakReference<MainActivity> mWeakReference;
public CountdownTimeHandler(MainActivity activity) {
this.mWeakReference = new WeakReference<>(activity);
}
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
//獲取對MainActivity的弱引用
MainActivity activity = mWeakReference.get();
switch (msg.what) {
case COUNTDOWN_TIME_CODE:
int value = msg.arg1;
activity.countdownTimeTextView.setText(String.valueOf(value--));
//循環發送消息的控制
if (value >= MIN_COUNT) {
Message message = Message.obtain();
message.what = COUNTDOWN_TIME_CODE;
message.arg1 = value;
sendMessageDelayed(message, DELAY_MILLIS);
}
break;
}
}
}
}
3、快捷鍵總結
Ctrl+Alt+F:改變變量的域
Ctrl+Alt+T:surrounded with快捷鍵
Ctrl+P:查看方法的參數