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是否可以从另一个动态资源中为动态资源赋值?
例如如何根据另一个动态资源定义动态资源的值?
<sys:Double x:Key="ButtonWidth">48</sys:Double>
<sys:Double x:Key="SmallButtonWidth"> ButtonWidth/2 </sys:Double>
是否可以从另一个动态资源中为动态资源赋值?
例如如何根据另一个动态资源定义动态资源的值?
<sys:Double x:Key="ButtonWidth">48</sys:Double>
<sys:Double x:Key="SmallButtonWidth"> ButtonWidth/2 </sys:Double>
,能够使用自定义MarkupExtension
变换的值。
例如
<Window.Resources xmlns:ms="clr-namespace:WpfApplication1.MathShit">
<sys:Double x:Key="ButtonWidth">48</sys:Double>
<ms:Calculation x:Key="SmallButtonWidth">
<ms:Product Operand1="{ms:Value {StaticResource ButtonWidth}}"
Operand2="0.5" />
</ms:Calculation>
</Window.Resources>
namespace WpfApplication1.MathShit
{
[ContentProperty("Expression")]
public class Calculation : MarkupExtension
{
public IExpression Expression { get; set; }
public override object ProvideValue(IServiceProvider serviceProvider)
{
if (Expression == null) throw new Exception("Expression cannot be null.");
return Expression.CalculateValue();
}
}
[TypeConverter(typeof(ExpressionConverter))]
public interface IExpression
{
double CalculateValue();
}
public abstract class BinaryOperation : IExpression
{
public IExpression Operand1 { get; set; }
public IExpression Operand2 { get; set; }
public double CalculateValue()
{
if (Operand1 == null) throw new Exception("Operand1 cannot be null.");
if (Operand2 == null) throw new Exception("Operand2 cannot be null.");
return CalculateBinaryOperation();
}
protected abstract double CalculateBinaryOperation();
}
public class Sum : BinaryOperation
{
protected override double CalculateBinaryOperation()
{
return Operand1.CalculateValue() + Operand2.CalculateValue();
}
}
public class Product : BinaryOperation
{
protected override double CalculateBinaryOperation()
{
return Operand1.CalculateValue() * Operand2.CalculateValue();
}
}
public class Value : MarkupExtension, IExpression
{
public double? Double { get; set; }
public Value() { }
public Value(double @double)
: this()
{
this.Double = @double;
}
public double CalculateValue()
{
if (Double == null) throw new Exception("Double");
return Double.Value;
}
// Allows easy object instantiation in XAML attributes. (Result of StaticResource is not piped through ExpressionConverter.)
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
}
public class ExpressionConverter : DoubleConverter
{
public override object ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value)
{
var doubleValue = (double)base.ConvertFrom(context, culture, value);
return (IExpression)new Value(doubleValue);
}
public override object ConvertTo(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value, Type destinationType)
{
var val = (Value)value;
return base.ConvertTo(context, culture, val.CalculateValue(), destinationType);
}
}
}
有了这个,你可以建立任意表达式树(这是很多比数学解析字符串,如果你不介意的麻烦,你可以做,当然也更容易)。