[英]XAML TwoWay binding to Nullable types
环境:WinRt / XAML / C#
我正在尝试对float类型的属性进行两种方式的绑定。 但是,如果那是可为null的类型(float?或Nullable),则绑定将不起作用。 我为此应用了事件转换器,它仍然没有显示任何可绑定性的迹象。
C#:ViewModel
public class MyViewModel : INotifyPropertyChanged
{
private float _quantity1;
public float Quantity1
{
get
{
return this._quantity1;
}
set
{
this._quantity1 = value;
RaisePropertyChanged("Quantity1");
}
}
private float? _quantity2;
public float? Quantity2
{
get
{
return this._quantity2;
}
set
{
this._quantity2 = value;
RaisePropertyChanged("Quantity2");
}
}
private Nullable<float> _quantity3;
public Nullable<float> Quantity3
{
get
{
return this._quantity3;
}
set
{
this._quantity3 = value;
RaisePropertyChanged("Quantity3");
}
}
public MyViewModel()
{
this.Quantity1 = 100.01F;
this.Quantity2 = 200.02F;
this.Quantity3 = 300.03F;
}
public event PropertyChangedEventHandler PropertyChanged;
protected void RaisePropertyChanged(string propertyName)
{
System.ComponentModel.PropertyChangedEventHandler propertyChanged = this.PropertyChanged;
if ((propertyChanged != null))
{
propertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs(propertyName));
}
}
}
C#:转换器:
public sealed class NullableFloatConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, string language)
{
if (value == null)
return 0F;
else
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
if (value != null)
return value;
else
return 0;
}
}
XAML:
<Page
x:Class="Test_Binding.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:Test_Binding"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Page.Resources>
<local:NullableFloatConverter x:Key="nullConverter" />
</Page.Resources>
<Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
<StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="Quantity1: " Width="150" />
<TextBox Text="{Binding Quantity1, Mode=TwoWay}" />
<TextBlock Text="{Binding Quantity1}" />
</StackPanel>
<!-- the second text block doesnt get an updated value -->
<StackPanel Orientation="Horizontal">
<TextBlock Text="Quantity2: " Width="150"/>
<TextBox Text="{Binding Quantity2, Mode=TwoWay, Converter={StaticResource nullConverter}}" />
<TextBlock Text="{Binding Quantity2, Converter={StaticResource nullConverter}}" />
</StackPanel>
<!-- the second text block doesnt get an updated value -->
<StackPanel Orientation="Horizontal">
<TextBlock Text="Quantity2 (No Converter): " Width="150"/>
<TextBox Text="{Binding Quantity2, Mode=TwoWay}" />
<TextBlock Text="{Binding Quantity2}" />
</StackPanel>
<!-- the second text block doesnt get an updated value -->
<StackPanel Orientation="Horizontal">
<TextBlock Text="Quantity3: " Width="150"/>
<TextBox Text="{Binding Quantity3, Mode=TwoWay}" />
<TextBlock Text="{Binding Quantity3}" />
</StackPanel>
</StackPanel>
</Grid>
仅“第一个”文本块被更新(例如,Quantity1)。 我无法获取其他(Quantity2和Quantity3)进行更新。 有什么建议么 ?
我认为convertBack方法并没有从头开始,这是我从stackoverflow.com/questions/15406336/databind-a-nullable-type-in-xaml-windows-8-store-app中获得的
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
string s = value as string;
float result;
if (!string.IsNullOrWhiteSpace(s) && float.TryParse(s, out result))
{
return result;
}
return null;
}
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