In WPF, what's the difference between null and Identity for RenderTransform?

Question

If I want to clear the RenderTransform on a UIElement, what is the preferred way to do it? Both seem to work:

MyGrid.RenderTransform = null;

or

MyGrid.RenderTransform = Transform.Identity;

Does anyone know the difference or if there will be any side effects by setting it to null?

From MSDN:

https://msdn.microsoft.com/en-us/library/system.windows.media.transform.identity(v=vs.110).aspx

When you apply an identity matrix, it does not change the object. It is like multiplying by 1.

Also, the default value for UIElement.RenderTransform is Transform.Identity.

https://msdn.microsoft.com/en-us/library/system.windows.uielement.rendertransform(v=vs.110).aspx

Answer 1

There is no difference. In UIElement.ArrangeCore source code you can see:

protected virtual void ArrangeCore(Rect finalRect)
{
    this.RenderSize = finalRect.Size;
    Transform transform = this.RenderTransform;
    if (transform == Transform.Identity)
        transform = (Transform) null;
    // the rest ...
}

So if RenderTransform is identity - it's treated as if it was null.

Answer 2

除此之外，如果将RenderTransform属性设置为null或Transform.Identity ，也没有太大的区别，您可能只想通过以下方式将属性重置为其默认值：

MyGrid.ClearValue(UIElement.RenderTransformProperty);