滑塊上的WPF綁定不會更新上最大更改

Question

• combobox1.SelectedItem綁定到SelectedItemProperty。
• 的時候SelectedItemProperty設置，MaxValueProperty計算

• MaxValueProperty勢必slider1.Maximum

• slider1.Value勢必SliderValueProperty

這些都做工精細，除了當combobox1.SelectedItem變化，MaxValueProperty是計算出來的，並且小於SliderValueProperty。

在查看：

• slider1.Maximum被更新，因爲MaxValueProperty改變，
• slider1.Value設置爲slider1.Maximum爲滑塊的默認行爲時，最大的變化小於該值。

然而，當這種情況發生，SliderValueProperty沒有更新到新slider1.Value

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

我知道slider1.Value正在得到改變，因爲我已經綁定了一個標籤，標籤更改

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

如何確保綁定更新？

Answer 1

而不是依靠滑塊的默認行爲和TwoWay綁定，你計算你的SelectedItemProperty二傳手新的最大後，首先在「SliderValueProperty」養PropertyChanged事件中使用新的最大值，然後第二次上「MaxValueProperty」。在私人支持領域進行計算，而不是在公共領域。

這將導致系統首先調整滑塊的值，然後將MAXVALUE，它應該移動滑塊位置爲您服務。

將slider1的Maximum的綁定模式設置爲OneWay;我認爲這會做到這一點。

與這樣的視圖模型如下：

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 

而XAML看起來有點像這樣：

<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>