Question

Below is my code from my activity. I call setKey() to set the key, but when I use getKey() it returns "";

public class SharedData {
    // This is a singleton class that provides a global data
    private SharedData instance = null;

    private SharedData() {
    }

    // Data to be shared
    private String key = "";

    public static SharedData getInstance() {
        instance = new SharedData();
        return instance;
    }

    public String getKey() {
        return key;
    }

    public void setKey(String skey) {
        key = skey;
    }
}

Answer 1

It seems that every time you are creating new instance for SharedData everytime

  public class SharedData {

        // this is a singleton class that provides a global data        
        private static SharedData instance = null;

        private SharedData() {

        }

        // data to be shared
        private String key = "";

        public static SharedData getInstance() {
            if (null == instance) {
            instance = new SharedData();
        }

        return instance;
        }


        public String getKey() {
            return key;
        }

        public void setKey(String skey) {
            key = skey;
        }
    }

now you need to below lines to use the same instance every time:

SharedData data = SharedData.getInstance();
data.setKey("some string");//to set value
data.getKey(); //to get value