Question

我有两个依赖属性，Value和MinVal 我希望默认值“Value”取决于“MinVal” 由xaml设置的“MinVal”只有一次我怎么能这样做？

以下是代码：

    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

基本上，您可以为依赖项属性添加强制方法。您的默认值位于元数据中。但是你希望值在加载XAML之后显示它们之前会相互作出反应，并且强制就是这样。

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;
}

元数据构造函数如下所示

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)
        ),
);

参考

依赖项属性默认值取决于另一个依赖项属性

1 个答案: