Dependency Property default value depend on another Dependency Property - wpf

Question

I have two Dependency Property, Value and MinVal.
I want the default value of "Value" will depend on "MinVal".
The "MinVal" set by xaml only one time.
How can I do that?
Here is the code:
public int Value
{
get { return (int)GetValue(ValueProperty); }
set { SetValue(ValueProperty, value); }
}
// Using a DependencyProperty as the backing store for Value. This enables animation, styling, binding, etc...
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register("Value", typeof(int), typeof(NumericHexUpDown), new UIPropertyMetadata(0, ValueChanged));
private static void ValueChanged(object sender, DependencyPropertyChangedEventArgs e)
{
}
public int MinVal
{
get { return (int)GetValue(MinValProperty); }
set { SetValue(MinValProperty, value); }
}
// Using a DependencyProperty as the backing store for MinVal. This enables animation, styling, binding, etc...
public static readonly DependencyProperty MinValProperty =
DependencyProperty.Register("MinVal", typeof(int), typeof(NumericHexUpDown), new UIPropertyMetadata(0, MinValueChanged));
private static void MinValueChanged(object sender, DependencyPropertyChangedEventArgs e)
{
}

Answer 1

Basically you add coerce methods to your dependency properties. Your default values are in the metadata. But you want the values to react to each other before they are displayed after the XAML is loaded, and coercion does just that.
private static void OnMinValChanged(DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
((NumericHexUpDown)d).CoerceValue(ValueProperty);
}
private static void OnValueChanged(DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
((NumericHexUpDown)d).CoerceValue(MinValProperty);
}
private static object CoerceMinVal(DependencyObject d,
object value)
{
double min = ((NumericHexUpDown)d).MinVal;
return value;
}
private static object CoerceValue(DependencyObject d,
object value)
{
double min = ((NumericHexUpDown)d).MinVal;
double val = (double)value;
if (val < min) return min;
return value;
}
The metadata constructor looks like this
public static readonly DependencyProperty MinValProperty = DependencyProperty.Register(
"MinVal", typeof(int), typeof(NumericHexUpDown),
new FrameworkPropertyMetadata(
0,
new PropertyChangedCallback(OnMinimumChanged),
new CoerceValueCallback(CoerceMinimum)
),
);
public static readonly DependencyProperty ValueProperty = DependencyProperty.Register(
"Value", typeof(int), typeof(NumericHexUpDown),
new FrameworkPropertyMetadata(
0,
new PropertyChangedCallback(OnValueChanged),
new CoerceValueCallback(CoerceValue)
),
);
References
http://drwpf.com/blog/2010/05/05/value-coercion-for-the-masses/
http://msdn.microsoft.com/en-us/library/ms745795.aspx