myapplication 单例写法

MyApplication extends Application
private static MyApplication myApplication = null;

oncreate中：

 @Override
    public void onCreate () {
        super.onCreate();
        myApplication = this;
       
    }

getInstance 函数

 public static MyApplication getInstance(){
        return myApplication;
    }

最重要一点，清单文件中：application 节点下：

  android:name=".MyApplication"