应用程序单例在Android中使用
我有一个facebook初始化sdk调用,我需要它来初始化应用程序启动的时刻:
我想使用我的Application类来做到这一点。 例如:
public class App extends Application { @Override public void onCreate() { super.onCreate(); FacebookSdk.sdkInitialize(getApplicationContext()); } }
我有facebook登录按钮的主要活动:
public class MainActivity extends AppCompatActivity { @BindView(R.id.login_button) LoginButton loginButton; private CallbackManager callbackManager; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ButterKnife.bind(this); callbackManager = CallbackManager.Factory.create(); loginButton.registerCallback(callbackManager, new FacebookCallback() { @Override public void onSuccess(LoginResult loginResult) { } @Override public void onCancel() { } @Override public void onError(FacebookException error) { } }); } }
如何调用我的应用程序单例? 如何使其onCreate()工作?
要使您的App类单例遵循Singleton设计模式:
public class App { // Create the instance private static App instance; public static App getInstance() { if (instance== null) { synchronized(App.class) { if (instance == null) instance = new App(); } } // Return the instance return instance; } private App() { // Constructor hidden because this is a singleton } public void initFBSdk() { FacebookSdk.sdkInitialize(getApplicationContext()); }
}
然后在任何其他类中使用它:
App.getInstance().initFBSdk();
如果这是你要求的..
当您扩展android.app.Application类时,您不必显式调用onCreate。 但请确保在AndroidManifest.xml中指定它,例如android:name =“完全限定名称”,例如:android:name =“com.example.MyApplication”
并且,要获取Application 的实例或您定义的Application的任何自定义子级,您只需调用context.getApplicationContext()即可 。 您不必实现Singleton模式。
参考https://developer.android.com/reference/android/app/Application.html
我想你正试图在java中创建一个线程安全的单例。 以下是我们的App
类所需的代码:
public class App extends Application { private static App instance; public static App getAppInstance() { return instance; } @Override public void onCreate() { super.onCreate(); instance = this; } public void initFacebookSdk() { FacebookSdk.sdkInitialize(getApplicationContext()); } }
这仅仅是对自身的引用。 我们想要实现Singleton for Multithreading。 然后我们将创建另一个类,在其构造函数中封装App
类,如下所示:
public class SingletonApp { private static App appInstance = null; private static SingletonApp instance = null; private static final Object mutex = new Object(); public static SingletonApp getInstance() { SingletonApp r = instance; if (r == null) { synchronized (mutex) { // While we were waiting for the sync, another r = instance; // thread may have instantiated the object. if (r == null) { r = new SingletonApp(); instance = r; } } } return r; } private SingletonDemo() { // Direct access the Application context calling appInstance = App.getAppInstance(); } public static getAppInstance() { return getInstance().appInstance; } }
然后在MainActivity
类中,您可以导入静态实例并在代码中使用它:
import static your.package.name.SingletonApp.getAppInstance;
例如,您可以在MainActivity
类中使用它,只需调用方法initFacebookSdk()
如下所示:
public class MainActivity extends AppCompatActivity { ... @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); initFacebookSdk(); ... } }