设置 ViewBox 的最大比例

Question

是否可以通过某种方式设置 ViewBox 中内容的最大比例？例如，如果我有这段代码，我想确保文本的缩放比例不超过 200%

<Grid>
    <Viewbox>
        <TextBox Text="Hello world" />
    </Viewbox>
</Grid>

Answer 1

您需要在 ViewBox 上设置 MaxWidth 和 MaxHeight:

<Grid>
    <Viewbox x:Name="MyViewBox">
        <TextBox x:Name="MyTextBox" Text="Hello world" />
    </Viewbox>
</Grid>

在后面的代码中：

MyViewBox.MaxWidth = MyTextBox.ActualWidth * 2d;
MyViewBox.MaxHeight = MyTextBox.ActualHeight * 2d;

或者更好的转换器解决方案：

public class ViewBoxMaxWidthOrHeightConverter : IValueConverter
{

    public object Convert(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        double textBoxWidthOrHeight = (double) value;
        return textBoxWidthOrHeight*2d;
    }

    public object ConvertBack(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new System.NotImplementedException();
    }
}

和XAML：

<local:ViewBoxMaxWidthOrHeightConverter x:Key="ViewBoxMaxWidthOrHeightConverter"/>
                <Grid>
                    <Viewbox x:Name="MyViewBox" 
                             MaxWidth="{Binding ElementName=MyTextBox, Path=ActualWidth, Converter={StaticResource ViewBoxMaxWidthOrHeightConverter}, Mode=OneWay}"
                             MaxHeight="{Binding ElementName=MyTextBox, Path=ActualHeight, Converter={StaticResource ViewBoxMaxWidthOrHeightConverter}, Mode=OneWay}">
                        <TextBox x:Name="MyTextBox" Text="Hello world" />
                    </Viewbox>
                </Grid>

Answer 2

对于未来的读者，我根据 user2250152 的回答编写了一个更优雅的方法，该方法使用附加的属性:

public static class ViewboxExtensions
{
    public static readonly DependencyProperty MaxZoomFactorProperty =
        DependencyProperty.Register("MaxZoomFactor", typeof(double), typeof(ViewboxExtensions), new PropertyMetadata(1.0, OnMaxZoomFactorChanged));

    private static void OnMaxZoomFactorChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var viewbox = d as Viewbox;
        if (viewbox == null)
            return;
        viewbox.Loaded += OnLoaded;
    }

    private static void OnLoaded(object sender, RoutedEventArgs e)
    {
        var viewbox = sender as Viewbox;
        var child = viewbox?.Child as FrameworkElement;
        if (child == null)
            return;

        child.SizeChanged += (o, args) => CalculateMaxSize(viewbox);
        CalculateMaxSize(viewbox);
    }

    private static void CalculateMaxSize(Viewbox viewbox)
    {
        var child = viewbox.Child as FrameworkElement;
        if (child == null)
            return;
        viewbox.MaxWidth = child.ActualWidth * GetMaxZoomFactor(viewbox);
        viewbox.MaxHeight = child.ActualHeight * GetMaxZoomFactor(viewbox);
    }

    public static void SetMaxZoomFactor(DependencyObject d, double value)
    {
        d.SetValue(MaxZoomFactorProperty, value);
    }

    public static double GetMaxZoomFactor(DependencyObject d)
    {
        return (double)d.GetValue(MaxZoomFactorProperty);
    }
}

附件属性可以像这样添加到视图框：

<Viewbox extensions:ViewboxExtensions.MaxZoomFactor="2.0">...</Viewbox>

设置 ViewBox 的最大比例

Set maximum scale of ViewBox

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