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自定义一个Range类型，利用CoerceValueCallback和PropertyChangeCallback实现三个属性Min,Max,Value，使其效果类似于Slider。Min总小于Max，并且Value总介于Min和Max之间。
public class Range : DependencyObject
{
public int Min
{
get { return (int)GetValue(MinProperty); }
set { SetValue(MinProperty, value); }
}
public int Max
{
get { return (int)GetValue(MaxProperty); }
set { SetValue(MaxProperty, value); }
}
public int Value
{
get { return (int)GetValue(ValueProperty); }
set { SetValue(ValueProperty, value); }
}
public static readonly DependencyProperty MinProperty;
public static readonly DependencyProperty MaxProperty;
public static readonly DependencyProperty ValueProperty;
public static FrameworkPropertyMetadata minMetadata;
public static FrameworkPropertyMetadata maxMetadata;
public static FrameworkPropertyMetadata valueMetadata;
static Range()
{
minMetadata = new FrameworkPropertyMetadata();
maxMetadata = new FrameworkPropertyMetadata(1); // Max的默认值为1
valueMetadata = new FrameworkPropertyMetadata();
minMetadata.CoerceValueCallback = MinCoerce;
maxMetadata.CoerceValueCallback = MaxCoerce;
valueMetadata.CoerceValueCallback = ValueCoerce;
minMetadata.PropertyChangedCallback = MinChanged;
maxMetadata.PropertyChangedCallback = MaxChanged;
MinProperty = DependencyProperty.Register("Min", typeof(int), typeof(Range), minMetadata);
MaxProperty = DependencyProperty.Register("Max", typeof(int), typeof(Range), maxMetadata);
ValueProperty = DependencyProperty.Register("Value", typeof(int), typeof(Range), valueMetadata);
}
public static object MinCoerce(DependencyObject d, object baseValue)
{
Range range = (Range)d;
if ((int)baseValue > range.Max)
return range.Max;
else
return (int)baseValue;
}
public static object MaxCoerce(DependencyObject d, object baseValue)
{
Range range = (Range)d;
if ((int)baseValue < range.Min)
return range.Min;
else
return (int)baseValue;
}
public static object ValueCoerce(DependencyObject d, object baseValue)
{
Range range = (Range)d;
int value = (int)baseValue;
if (value < range.Min)
return range.Min;
else if (value > range.Max)
return range.Max;
else
return value;
}
public static void MinChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
Range range = (Range)d;
range.CoerceValue(Range.MaxProperty); // Coerces the value of Dependcy Property
range.CoerceValue(Range.ValueProperty);
}
public static void MaxChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
Range range = (Range)d;
range.CoerceValue(Range.MinProperty);
range.CoerceValue(Range.ValueProperty);
}
}
// 执行以下语句，观察值的变化 Range range = new Range(); //Min=0, Max=1, Value=0 range.Value = 100; //Min=0, Max=1, Value=1 range.Min = 1; //Min=1, Max=1, Value=1 range.Max = 200; //Min=1, Max=200, Value=100
执行到最后一句时，当Max属性被改变之后，它会触发对Min和Value的强制。这一强制动作作用于最初设定的值。换句话说，WPF以依赖属性系统仍然保存了本地值100，并且现在该数值是可以接受的，它可以被应用到Value属性。
CoerceValueCallback 和 PropertyChangeCallBack
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原文地址：http://www.cnblogs.com/liuzeyuzh/p/4263931.html
