Creating widgets, setting/getting data from them - Pattern problem

Question

Lets say I have a Widget class. I also have TextWidget, ComboWidget, ChoiceWidget classes that inherited from Widget class.

I create this widgets based on the situation. After creating the widget, I just show some data on widget and get one from the user. After that the widget gets destroyed. My current code is something like this: (The code is totally arbitrary)

Widget createWidget(DataType type, Data data) {
    Widget widget;
    if (type == DataType.Text) {
        widget = new TextWidget();
        widget.setText(data.toStrig());
    } else if (type == DataType.Choice) {
        widget = new ChoiceWidget();
        widget.setChoices(data.toChoices())
    } else if (type == DataType.MultiText)
        widget = new ComboWidget();
        widget.setItems(data.toItems())
    }
    return widget;
}

After creating, I get some data from user using that widget. Then I just destroy it.

void widgetReturnPressedEvent(Widget widget) {
    UserData data;
    if (widget.type() == TextWidget)
        data.setText(((TextWidget)widget).getText())
    // ...
    // You get the idea.
}

I'm using this at different parts of my program. So doing if-else every time is not a good way to handle this situation. So what should I do here? Can something like this works, or is there a good pattern for this situation?

class DataWidget {
    Widget widget;
    Widget createWidget(DataType type) {
        Widget w;
        //...
        this.widget = w;
    }

    void setData(Data data) {
        if (this.widget == TextWidget)
            this.widget.setText(data.toString());
        //...
    }

    Data getData() {
        Data data;
        // set data
        return data;
    }

    Widget widget() {
        return this.widget;
    }
}

Answer 1

• Been there, done that. Factory Method Pattern.

• Factory has a static HashMap<String,WidgetCreator> so creating a widget is a matter of looking up it's creator in the Map and calling the create method. That's why no if or switchis needed.

• You can put all creators and the Factory in a separate package for a cleaner workspace.

• Also, as each type of Widget knows what method to call on Data, why not pass data instead?

• I assumed choises and items are List<String>, you can choose otherwise.

• UML first (this software paints interfaces purple instead of putting <<name>> in the title)

• Code bellow.

==> Factory.java <==

import java.util.HashMap;
import java.util.Map;

public class Factory {
    private static Map<String,WidgetCreator> widgetCreators = new HashMap<String,WidgetCreator>();

    static {
        widgetCreators.put("TEXT",new TextWidgetCreator());
        widgetCreators.put("CHOICE",new ChoiceWidgetCreator());
        widgetCreators.put("COMBO",new ComboWidgetCreator());
        // add as many creators as types od widgets you have
        // tags must be unique, feel free to use CONSTANSTS      
        // instead of magic literals for the tags
    }

    public static Widget getWidget(String tag) throws UnknownWidgetTagException{
        WidgetCreator c = widgetCreators.get(tag);
        if (c == null) {
            throw new UnknownWidgetTagException(tag);
        }
        return c;
    }
}

==> WidgetCreator.java <==

public interface WidgetCreator {
    public Widget createWidget(Data data);
}

==> Widget.java <==

public interface Widget {
    public void setData(Data data);
    public Data getData();
}

==> Data.java <==

import java.util.List;

public interface Data {
    public String toString();
    public List<String> toChoises();
    public List<String> toItems();
}

==> UnknownWidgetTagException.java <==

public class UnknownWidgetTagException extends Exception {

    public UnknownWidgetTagException(String tag) {
        System.out.println("No Widget registered with tag: "+tag);
    }

}

==> TextWidgetCreator.java <==

public class TextWidgetCreator implements WidgetCreator {

    @Override
    public Widget createWidget(Data data) {
        Widget w = new TextWidget();
        w.setData(data);
        return w;
    }

}

==> ChoiceWidgetCreator.java <==

public class ChoiceWidgetCreator implements WidgetCreator {

    @Override
    public Widget createWidget(Data data) {
        Widget w = new ChoiceWidget();
        w.setData(data);
        return w;
    }    
}

==> ComboWidgetCreator.java <==

public class ComboWidgetCreator implements WidgetCreator {

    @Override
    public Widget createWidget(Data data) {
        Widget w = new ComboWidget();
        w.setData(data);
        return w;       
    }
}

==> TextWidget.java <==

public class TextWidget implements Widget {

    private String text;
    private Data data;

    @Override
    public void setData(Data data) {
        this.data = data;
        this.text = data.toString();        
    }

    @Override
    public Data getData() {
        return data;
    }
}

==> ChoiceWidget.java <==

import java.util.List;

public class ChoiceWidget implements Widget {

    private List<String> choices;
    private Data data;

    @Override
    public void setData(Data data) {
        this.data = data;
        this.choices = data.toChoises();        
    }

    @Override
    public Data getData() {
        return data;
    }
}

==> ComboWidget.java <==

import java.util.List;

public class ComboWidget implements Widget {

    private List<String> items;
    private Data data;

    @Override
    public void setData(Data data) {
        this.data = data;
        this.items = data.toItems();        
    }

    @Override
    public Data getData() {
        return data;
    }

}

============

void widgetReturnPressedEvent(Widget widget) {
    UserData data;
    widget.setData(data); // widget already knows how to handle the data
}

===============