如何使用相同的事件处理程序在GWT（或Java AWT Swing）中的相同种类的多个对象上执行相同的功能

Question

I just started working on Gwt2.0. I have two textbox here. Both perform the same event operation. Using

addFocusListener()

What I have now is.

areaBox.addFocusListener(new FocusListener(){

        @Override
        @Deprecated
        public void onFocus(Widget arg0) {
            // TODO Auto-generated method stub
            areaBox.setTitle("Area");
        }
            @Override
            public void onLostFocus(Widget arg0) {
                if(areaBox.getText().length() >= 4 )
                {
                    areaBox.setStyleName("gwt-TextBox-Success");
                }
                else
                {
                    areaBox.setStyleName("gwt-TextBox-Error");
                    cityBox.setText("Enter Area Name ");
                    areaBox.addFocusListener(new FocusListener(){

                        @Override
                        @Deprecated
                        public void onFocus(Widget arg0) {
                            areaBox.setText(null);
                            areaBox.setStyleName("gwt-TextBox-AE");

                        }

                        @Override
                        @Deprecated
                        public void onLostFocus(Widget arg0) {

                        }

                    });

                }
            }

});
cityBox.addFocusListener(new FocusListener(){

    @Override
    @Deprecated
    public void onFocus(Widget arg0) {
        cityBox.setTitle("City");
    }
        @Override
        public void onLostFocus(Widget arg0) {
            if(cityBox.getText().length() >= 4 )
            {
                cityBox.setStyleName("gwt-TextBox-Success");
            }
            else
            {
                cityBox.setStyleName("gwt-TextBox-Error");
                cityBox.setText("Enter City Name ");

                cityBox.addFocusListener(new FocusListener(){

                    @Override
                    @Deprecated
                    public void onFocus(Widget arg0) {
                        cityBox.setText(null);
                        cityBox.setStyleName("gwt-TextBox-AE");

                    }

                    @Override
                    @Deprecated
                    public void onLostFocus(Widget arg0) {
                        // TODO Auto-generated method stub

                    }

                });

            }
        }

}); 

What the code does is. When Focused on Area TextBox, a tooltip appears, showing what to enter. When Focus on it is lost or comes to next textbox ie City TextBox, it checks whether the entered string is greater than 4 characters. if yes then SUCCESS css style is applied to the box, if not ERROR css style is applied. So, when clicked on it(AreaBox) again, The text is cleared and css style is reset.

The above is a sample between 2 textbox. Please help me, I have nearly 10 such fields, I want to minimize the code. I am thinking of using collections or custom widgets. But don't know where to start. Need your help and opinion. Thanks...

Answer 1

Here is how I would solve this problem:

areaBox.addFocusListener(generateFocusListener("Area", "Enter Area Name "));
cityBox.addFocusListener(generateFocusListener("City", "Enter City Name "));

FocusListener generateFocusListener(final String title, final String text) {
    return new FocusListener(){

            @Override
            @Deprecated
            public void onFocus(Widget widget) {
                // initial focus happens here
                TextBox box = (TextBox) widget;
                box.setTitle(title);
            }

            @Override
            public void onLostFocus(Widget widget) {
                // Focus is lost for the first time

                TextBox box = (TextBox) widget;
                if(box.getText().length() >= 4 )
                {
                    box.setStyleName("gwt-TextBox-Success");

                    // Change focus listener so that now once pressed it resets
                    box.addFocusListener(new FocusListener(){

                        @Override
                        @Deprecated
                        public void onFocus(Widget widget) {
                            TextBox box = (TextBox) widget;
                            box.setText(null);
                            box.setStyleName("gwt-TextBox-AE");
                        }

                        @Override
                        @Deprecated
                        public void onLostFocus(Widget widget) {
                            TextBox box = (TextBox) widget;
                            if(box.getText().length() >= 4 )
                            {
                                box.setStyleName("gwt-TextBox-Success");
                            }
                            else
                            {
                                box.setStyleName("gwt-TextBox-Error");
                                box.setText(text);
                            }

                        }

                    });
                }
                else
                {
                    box.setStyleName("gwt-TextBox-Error");
                    box.setText(text);
                }
            }

    };
}