Monday, June 28, 2010

A Chrome and Glass Theme- Part 8


In this post I’m going to show you how to make the radio buttons I blogged about previously. These buttons have gone through many iterations and I’m still not sure I’m quite happy with them just yet, but I’ll cover them anyway since they introduce a few interesting attached properties. Here is the sample I’ve been building up, now with the radio buttons:

You can grab the source here.

This post is the 8th in a series. If you are not familiar with styling controls in Blend, or working with Resource Dictionaries then I would recommend that you start at the beginning of the series.

The Radio Button

When I first attempted this button I ended up with horribly complicated arrangement of shapes to get it to scale properly. I had placeholders and spacers and grids within grids, with some of them having their height bound to their widths (which doesn’t work very well). And I had half circles on the ends with gradient blends merging seamlessly into the gradient blend on a rectangle in the middle. It was pretty awful.

The previous blog about Automatic Rectangle Radius X and Y should give you an idea of a simpler way to achieve the look. In the end I went with the attached properties since they work nicely both at run-time and design-time. If you grab the source from the link above, you may have to build it in Blend to get it to use the attached properties on the design surface.

The RadioButton inherits from the ToggleButton, as does the CheckBox. They all have a common theme of the button being checked, unchecked, or indeterminate; The radio button just has a different visual appearance, and adds the GroupName property. This style could be adapted for the ToggleButton too, but it wouldn’t really work as a style for a CheckBox.

The contents for this button are grouped in a grid with two columns; the left column contains the orb, the right column contains the ContentPresenter element.

Creating a custom style template for a radio button shouldn’t be difficult at all if you have been following along with the series, but I thought it might be worthwhile to look at some of the elements that make up this button.

Scalable Rounded Ends

A rectangle has the RadiusX and RadiusY properties that let you turn the sharp corners into rounded corners. For this button I want the rounded ends to stay rounded, at the right proportion, regardless of the size of the button. Unfortunately, there is no easy way to set those properties to be half of the height of the rectangle.

As mentioned in the post about Automatic Rectangle Radius X and Y I used an attached property to achieve the rounded ends since that gave me the best result when working with Blend. I use 3 rectangles in the button: one for the rim using the ChromeBorder resource brush, one for the main body using the ChromeFill resource brush, and one the same size that uses the ChromeDarkeningLinear resource brush to make the white text stand out better.

The ellipse is used on the right end of the button to add some dark shading to make the button look rounder, and the Orb grid uses the same principle as this post.

I created an attached property called IsRounded that, when true, uses another attached property called RoundCapsRatio (which defaults to 0.5 if unset) that it multiplies against height or width (whichever is smaller) and applies to the RadiusX and RadiusY properties of the rectangle it is attached to. You may have to build the solution once in Blend to have it applied properly, but then the corner radius automatically updates in blend as the rectangle it is applied to changes size.

Scalable Orb

The other attached properties I created are WidthRatio and HeightRatio (not used in this example). I use the WidthRatio attached property on the Orb grid to keep it perfectly square so the ellipses inside it stay round. I can’t have this happen without an attached property because there is no other way (that works in Blend) to set the width of an element to be relative to the height. I set the WidthRatio to the value “1” to achieve this. I could have just used a Boolean attached property, but having the ratio makes it more reusable.

If you use both the attached properties on a visual element, the handler will prefer the WidthRatio over the HeightRatio. Here is the method that applies the property values. It only applies the values if they have actually been set:

   1: private static void UpdateSizeRatio(FrameworkElement element)
   2: {
   3:     double ratio;
   4:     if (element.ReadLocalValue(WidthRatioProperty) != DependencyProperty.UnsetValue)
   5:     {
   6:         ratio = (double)element.GetValue(WidthRatioProperty);
   7:         double height = element.ActualHeight;
   8:         if (!double.IsNaN(height) && height > 0)
   9:         {
  10:             element.Width = height * ratio;
  11:         }
  12:     }
  13:     else if (element.ReadLocalValue(HeightRatioProperty) != DependencyProperty.UnsetValue)
  14:     {
  15:         ratio = (double)element.GetValue(HeightRatioProperty);
  16:         double width = element.ActualWidth;
  17:         if (!double.IsNaN(width) && width > 0)
  18:         {
  19:             element.Height = width * ratio;
  20:         }
  21:     }
  22: }


As far as radio buttons go, these are fairly limited in their application since they are so big. They are too big to use in the same way as you would normally use a radio button, but they do make quite good navigation buttons instead of using tabs.

The use of Attached Properties seems the best solution for adding behavior to a visual element that works at design time in Blend, but it’s not ideal – I would really rather have a way to do this using Blend that didn’t need me to swap into the XAML.


The icons are from the Tango Desktop Project.

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