如何将Xamarin.Forms条目绑定到非字符串类型,例如Decimal

Question

我创建了Entry,我试图将它绑定到Decimal属性,如下所示:

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输入Entry时,我收到以下错误.

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

Answer 1

在撰写本文时,在绑定时没有内置转换(但这是有效的),因此绑定系统不知道如何将DownPayment字段(小数)转换为Entry.Text(字符串).

如果OneWay绑定是您所期望的,字符串转换器将完成这项工作.这适用于Label:

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

对于a Entry,您希望绑定在两个方向都有效,因此您需要一个转换器:

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,您可以在绑定中使用该转换器的实例:

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