Callback with extended EditText

Question

I'm trying to create a custom EditText that provides an onLostFocus event. However, I can't get my head around how I tell the custom class what method to run when the focus is lost.

This is my extended EditText:

public class smtyEditText extends EditText {    
    public smtyEditText(Context context) {
        super(context);
    }

    public smtyEditText(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public smtyEditText(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public void setFocusChangeListener() {
        this.setOnFocusChangeListener(new View.OnFocusChangeListener() {
            public void onFocusChange(View v, boolean hasFocus) {
                if (!hasFocus) {
                    // notify the relevant activity, probably passing it some parameters like what instance of smtyEditText triggered the event.    
                }
            }
        });
    }
}

The intention of the setFocusChangeListener function was that from any given activity I could do something like:

public class AddMeal extends ActionBarActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_meal);

        EditText etMealName = (EditText) findViewById(R.id.txtmealName);
        etMealName.setFocusChangeListener(this.fieldLostFocus)
    }

    // then
    public void fieldLostFocus(eventSource) {
        // run some kind of validation on the field text.
    }
}

Clearly I'm "code paraphrasing" here. I also get that Interfaces, and some other "EventNotifier" class might be needed. These are the resources I've tried to decipher so far:

• http://www.javaworld.com/article/2077462/learn-java/java-tip-10--implement-callback-routines-in-java.html
• How to Define Callbacks in Android?
• http://www.justinmccandless.com/blog/Setting+Up+a+Callback+Function+in+Android

But for whatever reason I can't crystallize what is needed. Do you have any suggestions on how I can achieve this?

Answer 1

You don't need the inheritance... it only adds an unnecessary layer of indirection. Just add the focus change handler in your activity.

public class AddMeal extends ActionBarActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_meal);

        EditText etMealName = (EditText) findViewById(R.id.txtmealName);
        etMealName.setFocusChangeListener(new View.OnFocusChangeListener() {
        public void onFocusChange(View v, boolean hasFocus) {
            if (!hasFocus) {
                // call method to handle loss of focus 
            }
        }
    });
    }

    // then
    public void fieldLostFocus(eventSource) {
        // run some kind of validation on the field text.
    }
}