Question

我只需要运行一次函数（当它晚上，更改图像视图的图像），当我在oncreate（）中使用它时，它每次启动时都会运行活性。

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
                startAnim();
    }
}

private void startAnim(){
    Date dateNow=new Date();
    SimpleDateFormat sdf=new SimpleDateFormat("yy-MM-dd HH:mm:ss");
    String night=String.format("%tF",dateNow)+" 19:00:00";
    try {
        Date dateNight=sdf.parse(night);
        if(dateNow.after(dateNight)){
             DisplayMetrics metric = new DisplayMetrics();
            getWindowManager().getDefaultDisplay().getMetrics(metric);
            int width = metric.widthPixels;  // 屏幕宽度（像素）
            int height = metric.heightPixels;  // 屏幕高度（像素）
            RotateAnimation ra=new RotateAnimation(0,100,width/2,height/2-80);
            ra.setDuration(4000);
            sunMoon.startAnimation(ra);
              } catch (ParseException e) {
        e.printStackTrace();
    }
}
}

Answer 1

记录上次在文件中运行startAnim()的时间。当您开始活动以决定是否运行startAnim()时，请阅读此文件。

Answer 2

共享首选项中的文件或商店。保存方法的示例：

public String reverseString( String str )
{
    if(str.length()==1){
        return str;
    }
    return str.charAt( str.length() - 1 ) + reverseString( str.substring( 0, str.length() - 1 ) );

}
// initialize pos to 0
public int getLargest( int[] arr, int pos )
{
    int largest = arr[pos];
    if ( pos + 1 >= arr.length ) {
        return largest;
    }

    int second = getLargest( arr, pos + 1 );
    return largest > second ? largest : second;
}

示例检查：

private void saveLastRanTime(String key, long lastRunTime) {
    SharedPreferences prefs = getApplicationContext().getSharedPreferences(getPackageName(), Context.MODE_PRIVATE);
    SharedPreferences.Editor editor = prefs.edit();
    editor.putLong(key, lastRunTime); // Store the key somewhere instead of passing in each time
    editor.apply();
}

这将使你的startAnim（）方法看起来更像：

private boolean wasLastRunToday(String keyOfPreference) {
    SharedPreferences prefs = getApplicationContext().getSharedPreferences(getPackageName(), Context.MODE_PRIVATE);
    long lastRanAt = prefs.getLong(keyOfPreference, -1); // Save key somewhere..
    if (lastRanAt == -1) { // In the event it was never saved before.
       return false;
    }

    Calendar cal = Calendar.getInstance();
    cal.setTimeInMillis(lastRanAt);
    int dayLastRanAt = cal.get(Calendar.DAY_OF_YEAR);

    cal.setTimeInMillis(System.currentTimeMillis());
    int today = cal.get(Calendar.DAY_OF_YEAR);

    return today == dayLastRanAt;
}

如何只运行一次函数

2 个答案: