doing some mathematical calculation on custom dependency property values - wpf

Question

I have three dependency property. TestControlHeight, HalfValue1 and HalfValue2. Now, depending on these three value I have to calculate
a third value which will be assigned as the height of the inner control which will also be a dependency property.
height of inner control = TestControlHeight/ (HalfValue1 - HalfValue2);
Where can I write this code to calculate the height of the inner control (which si also a dependency property)
public static readonly DependencyProperty TestControlHeightProperty =
DependencyProperty.Register("TestControlHeight", typeof (double),
typeof (TestControl), new PropertyMetadata(default(double)));
public double TestControlHeight
{
get { return (double) GetValue(TestControlHeightProperty); }
set { SetValue(TestControlHeightProperty, value); }
}
public static readonly DependencyProperty HalfValue1Property =
DependencyProperty.Register("HalfValue1", typeof (double), typeof
(TestControl), new PropertyMetadata(default(double)));
public double HalfValue1
{
get { return (double) GetValue(HalfValue1Property); }
set { SetValue(HalfValue1Property, value); }
}
public static readonly DependencyProperty HalfValue2Property =
DependencyProperty.Register("HalfValue2", typeof (double), typeof
(TestControl), new PropertyMetadata(default(double)));
public double HalfValue2
{
get { return (double) GetValue(HalfValue2Property); }
set { SetValue(HalfValue2Property, value); }
}
Thanks & Regards,

Answer 1

From the WPF Unleashed book:
.NET property wrappers are bypassed at runtime when setting dependency properties
in XAML!
Although the XAML compiler depends on the property wrapper at compile time, WPF calls the underlying GetValue and SetValue methods directly at runtime! Therefore, to maintain parity between setting a property in XAML and procedural code, it’s crucial that property wrappers not contain any logic in addition to the GetValue/SetValue calls.
If you want to add custom logic, that’s what the registered callbacks are for. All of WPF’s built-in property wrappers abide by this rule, so this warning is for anyone writing a custom class with its own dependency properties.
So, your code could look like this (not tested):
public static readonly DependencyProperty TestControlHeightProperty =
DependencyProperty.Register("TestControlHeight", typeof(double), typeof(TestControl),
new PropertyMetadata(false, new PropertyChangedCallback(OnHeightChanged)));
public double TestControlHeight
{
get { return (double)GetValue(TestControlHeightProperty); }
set { SetValue(TestControlHeightProperty, value); }
}
public static readonly DependencyProperty HalfValue1Property =
DependencyProperty.Register("HalfValue1", typeof(double), typeof(TestControl),
new PropertyMetadata(false, new PropertyChangedCallback(OnHeightChanged)));
public double HalfValue1
{
get { return (double)GetValue(HalfValue1Property); }
set { SetValue(HalfValue1Property, value); }
}
public static readonly DependencyProperty HalfValue2Property =
DependencyProperty.Register("HalfValue2", typeof(double), typeof(TestControl),
new PropertyMetadata(false, new PropertyChangedCallback(OnHeightChanged)));
public double HalfValue2
{
get { return (double)GetValue(HalfValue2Property); }
set { SetValue(HalfValue2Property, value); }
}
public double MyInnerControlHeight
{
get { return (double)GetValue(MyInnerControlHeightPropertyProperty); }
set { SetValue(MyInnerControlHeightPropertyProperty, value); }
}
public static readonly DependencyProperty MyInnerControlHeightPropertyProperty =
DependencyProperty.Register("MyInnerControlHeightProperty", typeof(double), typeof(TestControl),
new PropertyMetadata(0));
private static void OnHeightChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var testControl = d as TestControl;
if (testControl != null)
{
testControl.MyInnerControlHeight = testControl.TestControlHeight / (testControl.HalfValue1 - testControl.HalfValue2);
}
}