如何在 `onCreate()` 中只调用一次方法并在更改活动时保持 运行

Question

所以我有一个应用程序，它会在驾驶 4 小时后告诉您应该休息。当用户继续另一个 activity（比方说 settings 选项卡）并返回主 activity 时，该计时器从 0 重新开始。我如何停止它？

Answer 1

您可以通过多种方式解决该问题。

首先，您可以创建一个单例class。操作定时器。这样它就不会死。 二、可以在intent中传递对象 第三，您可以 运行 应用程序外的计时器 class 而不是 activity.

1. https://www.geeksforgeeks.org/singleton-class-java/

   class Timer{
       private static Timer timer=null;
           public get_instance(){
           if(timer==null){
              timer=new Timer();
           }
       return timer;
       }
   }
   

2. 使用意图传递

//To pass:
    intent.putExtra("MyTimer", obj);

// To retrieve object in second Activity
    getIntent().getSerializableExtra("MyTimer");

3. 正在使用应用程序 activity

    import android.app.Application;
   
    public class MyCustomApplication extends Application {
        // Called when the application is starting, before any other application objects have been created.
        // Overriding this method is totally optional!
        @Override
        public void onCreate() {
            super.onCreate();
            startTimer(); // This might be a better place for it
            // Required initialization logic here!
        }
   
        // Called by the system when the device configuration changes while your component is running.
        // Overriding this method is totally optional!
        @Override
        public void onConfigurationChanged(Configuration newConfig) {
            super.onConfigurationChanged(newConfig);
        }
   
        // This is called when the overall system is running low on memory, 
        // and would like actively running processes to tighten their belts.
        // Overriding this method is totally optional!
        @Override
        public void onLowMemory() {
            super.onLowMemory();
        }
    }