android - Android中的单例

Question

我已关注此链接并成功在 Android 中制作了单例类。 http://www.devahead.com/blog/2011/06/extending-the-android-application-class-and-dealing-with-singleton/

问题是我想要一个对象。就像我有 Activity A 和 Activity B。在 Activity A 中，我从 Singleton class 访问对象.我使用该对象并对其进行了一些更改。

当我移动到 Activity B 并从 Singleton Class 访问对象时，它给了我初始化的对象，并且不保留我在 Activity A 中所做的更改。有没有其他方法可以保存更改？请高手帮帮我。这是MainActivity

public class MainActivity extends Activity {
    protected MyApplication app;        
    private OnClickListener btn2=new OnClickListener() {    
        @Override
        public void onClick(View arg0) {
            Intent intent=new Intent(MainActivity.this,NextActivity.class);
            startActivity(intent);              
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Get the application instance
        app = (MyApplication)getApplication();

        // Call a custom application method
        app.customAppMethod();

        // Call a custom method in MySingleton
        Singleton.getInstance().customSingletonMethod();

        Singleton.getInstance();
        // Read the value of a variable in MySingleton
        String singletonVar = Singleton.customVar;

        Log.d("Test",singletonVar);
        singletonVar="World";
        Log.d("Test",singletonVar);

        Button btn=(Button)findViewById(R.id.button1);
        btn.setOnClickListener(btn2);
    }

}

这是 NextActivity

public class NextActivity extends Activity {

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

            String singletonVar = Singleton.customVar;

            Log.d("Test",singletonVar);
        }
  }

Singleton类

public class Singleton
{
    private static Singleton instance;

    public static String customVar="Hello";

    public static void initInstance()
    {
    if (instance == null)
    {
      // Create the instance
      instance = new Singleton();
    }
    }

    public static Singleton getInstance()
    {
     // Return the instance
     return instance;
     }

     private Singleton()
     {
     // Constructor hidden because this is a singleton
     }

     public void customSingletonMethod()
     {
     // Custom method
     }
 }

和MyApplication

public class MyApplication extends Application
    {
    @Override
    public void onCreate()
    {
    super.onCreate();

     // Initialize the singletons so their instances
     // are bound to the application process.
     initSingletons();
     }

     protected void initSingletons()
     {
     // Initialize the instance of MySingleton
     Singleton.initInstance();
     }

     public void customAppMethod()
     {
     // Custom application method
    }
}

当我运行这段代码时，我得到了我在 Singleton 中初始化的 Hello然后是我在 MainActivity 中给出的 World并再次在 NextActivity 中显示 Hello在日志中。我希望它在 NextActivity 中再次向世界展示.请帮我纠正这个问题。

Answer 1

提示:在 Android Studio 中创建单例类，右键单击您的项目并打开菜单:

New -> Java Class -> Choose Singleton from dropdown menu