如何将Xamarin.Forms条目绑定到非字符串类型(如Decimal) [英] How to bind Xamarin.Forms Entry to a Non String Type such as Decimal

问题描述

我已经创建了Entry，并且正在尝试将其绑定到Decimal属性，例如:

I have and Entry created and I am trying to bind it to a Decimal property like such:

var downPayment = new Entry () {
    HorizontalOptions = LayoutOptions.FillAndExpand,
    Placeholder = "Down Payment",
    Keyboard = Keyboard.Numeric
};
downPayment.SetBinding (Entry.TextProperty, "DownPayment");

当我尝试在模拟器上键入Entry时，出现以下错误.

I am getting the following error when I try to type into the Entry on the simulator.

对象类型System.String无法转换为目标类型:System.Decimal

Object type System.String cannot be converted to target type: System.Decimal

推荐答案

在撰写本文时，在绑定时没有内置的转换(但是可以进行此操作)，因此绑定系统不知道如何将您的DownPayment字段(十进制)转换为Entry.Text(字符串).

At the time of this writing, there are no built-in conversion at binding time (but this is worked on), so the binding system does not know how to convert your DownPayment field (a decimal) to the Entry.Text (a string).

如果您希望使用OneWay绑定，则将使用字符串转换器完成此工作.这对于Label:

If OneWay binding is what you expect, a string converter will do the job. This would work well for a Label:

downPayment.SetBinding (Entry.TextProperty, new Binding ("DownPayment", stringFormat: "{0}"));

对于Entry，您希望绑定在两个方向上都有效，因此您需要一个转换器:

For an Entry, you expect the binding to work in both direction, so for that you need a converter:

public class DecimalConverter : IValueConverter
{
    public object Convert (object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value is decimal)
            return value.ToString ();
        return value;
    }

    public object ConvertBack (object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        decimal dec;
        if (decimal.TryParse (value as string, out dec))
            return dec;
        return value;
    }
}

现在您可以在Binding中使用该转换器的实例:

and you can now use an instance of that converter in your Binding:

downPayment.SetBinding (Entry.TextProperty, new Binding ("DownPayment", converter: new DecimalConverter()));

注意:

OP的代码应该在1.2.1及更高版本中开箱即用(来自Stephane对问题的评论).对于低于1.2.1的版本，这是一种解决方法

OP's code should work out of the box in version 1.2.1 and above (from Stephane's comment on the Question). This is a workaround for versions lower than 1.2.1

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