ScaleTransform 有什么用？

Question

why I should use ScaleX="2" for example instead of double the width of my control??

<Button Width = "100" Content="Button1"/>


<Button Width = "50" Content="Button2">
   <Button.RenderTransform>
      <ScaleTransform ScaleX="2" />
   </Button.RenderTransform>
</Button>

both buttons look exactly the same so again, what scale is good for

Answer 1

Your concept of "exactly the same" seems to be different from mine.

The sizes you specify with Width and Height affect how much space the control takes up in the layout, this means that the control may take more or less space but the font size will stay the same for example. The RenderTransform is a manipulation on top of this which no longer concerns the layout and hence may distort the control.

A render transform does not regenerate layout size or render size information. Render transforms are typically intended for animating or applying a temporary effect to an element. For example, the element might zoom when focused or moused over, or might jitter on load to draw the eye to that part of the user interface (UI).

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See also the LayoutTransform property, which does affect layout but still distorts the control.

Answer 2

It's useful when you don't have the ability to scale some parts of a control. Consider the DatePicker control. The default implementation has a drop-down calendar that was too small for my users' liking, so I introduced this snippet of XAML into my App.xaml file:

<Style TargetType="w:DatePicker">
    <Setter Property="CalendarStyle">
        <Setter.Value>
            <Style TargetType="w:Calendar">
                <Setter Property="LayoutTransform">
                    <Setter.Value>
                        <ScaleTransform ScaleX="1.5" ScaleY="1.5" />
                    </Setter.Value>
                </Setter>
            </Style>
        </Setter.Value>
    </Setter>
</Style>

Now the calendar is 1.5 times as big, and my users are happy. There is no "CalendarWidth" or "CalendarHeight" property that I can set directly, so the ScaleTransform saved the day.

Answer 3

What if it was more complicated than a Button with a Width? What if you had a complex Path/Geometry, or maybe even a group of controls? You wouldn't want to go and manually change everything. What if you had a custom control, where you wanted to give one instance the size 100x100, and another instance 150x150? What if you were implementing zoom functionality (think google maps)?

In short, for your specific example, it doesn't provide much use. But there are many other cases where it does.