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AL_it
AL_it
Associate II
June 12, 2019
Solved

How to create a custom widget class by combining two(or more) existing widget classes?

  • June 12, 2019
  • 6 replies
  • 1663 views

I tried to create a TextBox widget which derived from Box widget and TextArea widget. Because of its multiple inheritances, I also made minor changes to library files by adding keyword "virtual" to solve ambiguity error("base class"touchgfx::Drawable" is ambiguous). Project compiled but it still didn't work.

I would like to know how to create a custom widget class if it's possible. Thank you.

This topic has been closed for replies.
Best answer by Martin KJELDSEN

Multiple inheritance of widgets is not the right way to go about creating custom widgets and you definitely should not have to modify core files.

One option, like @Community member​ suggests is to create a Custom Container through the designer interface that has a Box and a textarea on top. That container is reusable through your application.

Another option is to write your own c++ class, inherit from, e.g. Box and then use the draw() method to draw text. If you're interested in this i can show you an example. This class won't be usable through the designer.

A third option is to write templates that you can use to add the same functionality to a number of drawables (This is what we've done with Draggable, ClickListener, FadeAnimator, MoveAnimator that you can find in touchgfx/mixins/. These mixins are applicable through the designer for any drawable.

Let me know what you think

/Martin

6 replies

cameronf
cameronf
Associate
June 12, 2019

I don't know why what you're trying to do wouldn't work, though I would be hesitant to change library files, even just to switch to virtual inheritance from Drawable (also don't know if Box and TextArea sharing their Drawable members would break anything, even if it didn't, you're limited to making changes to the Drawable for both of them (rect size, etc)).

It may be easier to make a custom container that just has a Box and a TextArea in it and then you can configure them both separately.

If you provide source code for your widget and detail about what's not working someone might be able to help you with making it work as a custom widget though.

AL_it
AL_itAuthor
Associate II
June 13, 2019

Thank you for answering my question. I think I broke something when I did virtual inheritance. In TextArea.hpp file, I made a small change like this, class TextArea : virtual public Widget. After this change, textarea widget is no longer working, no texts display on screen, and when I called resizeToCurrentText() function, application generated exception thrown error(Access violation executing location 0x006E0069).

Those unexpected behaviors occur when I used virtual inheritance for TextArea widget class. My custom widget code didn't cause these behaviors, because I removed it from project.

I think I should use custom container instead as you suggested.

Martin KJELDSEN
Martin KJELDSENBest answer
Principal III
June 13, 2019

Multiple inheritance of widgets is not the right way to go about creating custom widgets and you definitely should not have to modify core files.

One option, like @Community member​ suggests is to create a Custom Container through the designer interface that has a Box and a textarea on top. That container is reusable through your application.

Another option is to write your own c++ class, inherit from, e.g. Box and then use the draw() method to draw text. If you're interested in this i can show you an example. This class won't be usable through the designer.

A third option is to write templates that you can use to add the same functionality to a number of drawables (This is what we've done with Draggable, ClickListener, FadeAnimator, MoveAnimator that you can find in touchgfx/mixins/. These mixins are applicable through the designer for any drawable.

Let me know what you think

/Martin

AL_it
AL_itAuthor
Associate II
June 13, 2019

Thank you for answering my question. I think I will go with first option - using custom container, it's definitely the easiest solution to implement.

When I tried to use virtual inheritance, I did something like this (class TextArea : virtual public Widget ) in TextArea.hpp. After this simple change, textarea widget stopped working, no texts display on screen, and got exception thrown error when resizeToCurrentText() function is called. No sure why these kinda behaviors occur.

And If you don't mind, can you show me the example how to use draw()method to draw text in Second Option. It also sounds interesting to me.

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