无法从 UWP 文本框保存小数属性 [英] Cannot Save Decimal Property from UWP TextBox

问题描述

我在 UWP 中有 2 个文本框.它们绑定到模型实体上的整数和小数属性.整数属性被保存，但小数返回错误

I have 2 TextBoxes in UWP. They are bound to integer and decimal properties on the model entity. The integer property is saved but the decimal returns the error

Cannot save value from target back to source. BindingExpression: Path='ComponentDec' DataItem='Orders.Component'; target element is 'Windows.UI.Xaml.Controls.TextBox' (Name='null'); target property is 'Text' (type 'String').

相关的 XAML 是:

The relevant XAML is:

                    <ListView
                        Name="ComponentsList"
                        ItemsSource="{Binding Components}">
                        <ListView.ItemTemplate>
                            <DataTemplate>
                                <StackPanel Orientation="Horizontal">
                                    <TextBox Text="{Binding ComponentInt,Mode=TwoWay}"></TextBox>
                                    <TextBox Text="{Binding ComponentDec,Mode=TwoWay,Converter={StaticResource ChangeTypeConverter}}"></TextBox>
                                </StackPanel>
                            </DataTemplate>
                        </ListView.ItemTemplate>
                    </ListView>

实体类:

public class Component
{
    public string ComponentCode { get; set; }
    public string ComponentDescription { get; set; }
    public int ComponentInt { get; set; }
    public decimal ComponentDec { get; set; }
    public override string ToString()
    {
        return this.ComponentCode;
    }
}

转换器无耻地从模板 10 中借用:

The converter was shamelessly borrowed from Template 10:

public class ChangeTypeConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        if (targetType.IsConstructedGenericType && targetType.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
        {
            if (value == null)
            {
                return null;
            }
            targetType = Nullable.GetUnderlyingType(targetType);
        }

        if (value == null && targetType.GetTypeInfo().IsValueType)
            return Activator.CreateInstance(targetType);

        if (targetType.IsInstanceOfType(value))
            return value;

        return System.Convert.ChangeType(value, targetType);
    }

为什么小数属性不保存?

Why doesn't the decimal property save?

推荐答案

我通过将 Binding ComponentDec 更改为 x:Bind ComponentDec

我认为这是因为 x:Bind 允许将 targetType 作为 System.Decimal 传递.而 Binding 将 targetType 作为 System.Object 传递.

I think this is because x:Bind allows targetType to be passed as System.Decimal. Whereas Binding passes the targetType as System.Object.

要使用 Binding，我需要按照 @schumi1331 的建议编写一个 DecimalConverter.

To use Binding I will need to write a DecimalConverter as @schumi1331 suggested.

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