Slider上的WPF绑定不会在最大更改时更新

Question

• combobox1.SelectedItem绑定到SelectedItemProperty。
• 设置SelectedItemProperty时，计算MaxValueProperty

• MaxValueProperty绑定到slider1.Maximum

• slider1.Value绑定到SliderValueProperty

这些都可以正常工作，除非combobox1.SelectedItem更改，MaxValueProperty已计算，并且小于SliderValueProperty。

在视图中：

• slider1.Maximum已更新，因为MaxValueProperty已更改，
• slider1.Value设置为slider1.Maximum作为滑块的默认行为，当max更改为小于该值时。

但是，如果发生这种情况，SliderValueProperty不会更新为新slider1.Value

<Slider Name="slider1" Maximum="{Binding Path=MaxValueProperty, Mode=TwoWay}" Value="{Binding Path=SliderValueProperty, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />

我知道slider1.Value正在改变，因为我有一个标签绑定它，标签改变了

<Label Content="{Binding ElementName=slider, Path=Value, Converter={StaticResource NumberToStringConverter}}" />

如何确保更新绑定？

Answer 1

在计算TwoWay setter PropertyChanged绑定，而是引发SelectedItemProperty事件>，首先使用新的最大值在“SliderValueProperty”上，然后在“MaxValueProperty”上使用第二个。在您的私人支持字段上进行计算，而不是在公共属性上进行计算。

这将导致系统首先调整滑块的值，然后调整maxvalue，它应该为您移动滑块位置。

将slider1的Maximum上的绑定模式设置为OneWay;我认为这样做会有所帮助。

如下所示使用这样的viewmodel：

Class viewmodel
    Implements INotifyPropertyChanged
Private _selectedItemProperty As ComboBoxItem
Public Property SelectedItemProperty As ComboBoxItem

    Get
        Return _selectedItemProperty
    End Get
    Set(value As ComboBoxItem)
        MaxValueProperty = value.Content
        If _sliderValueProperty > _maxValueProperty Then _sliderValueProperty = _maxValueProperty
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("MaxValueProperty"))
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("SliderValueProperty"))
    End Set
End Property
Private _maxValueProperty, _sliderValueProperty as Single
Public Property MaxValueProperty As Single ' with setter that will raise PropertyChanged and use the backing field

'...

Public Property SliderValueProperty As Single ' with a setter that will raise PropertyChanged and use the backing field

'...

End Class

XAML看起来有点像这样：

    <Grid>
    <ComboBox Height="23" HorizontalAlignment="Left" Margin="40,38,0,0" Name="ComboBox1" VerticalAlignment="Top" Width="120" SelectedItem="{Binding SelectedItemProperty}">
        <ComboBoxItem Content="50" />
        <ComboBoxItem Content="30" />
        <ComboBoxItem Content="10" />
    </ComboBox>
    <Slider Name="slider1" Height="23" HorizontalAlignment="Left" Margin="87,135,0,0"  VerticalAlignment="Top" Width="100" Value="{Binding SliderValueProperty}" Minimum="1" Maximum="{Binding MaxValueProperty}" />
    <Label Content="{Binding ElementName=slider1, Path=Value}" Margin="40,174,293,96" />

</Grid>