Question

我正在使用Xamarin和MvvmCross为Android开发应用程序。在我的axml中，我定义了EditText：

<EditText
    local:MvxBind="Text PorcentagemDesconto"
    android:inputType="number"
    android:layout_width="1dp"
    android:layout_weight="0.3"
    android:layout_height="wrap_content"
    android:hint="%" />

PorcentagemDesconto 字段以这种方式声明：

private decimal? _porcentagemDesconto;
public decimal? PorcentagemDesconto
{
    get { return _porcentagemDesconto; }
    set
    {
        _porcentagemDesconto = value;
    }
}

我们说我在EditText上插入值 256 。然后，我在属性的set方法上插入一个断点，然后，删除所有数字（按退格键3次），断点只会被 2次，将私有变量保留为 2 的非期望值。

这方面有一些解决方法，或者我在这里做错了什么？

Answer 1

这是因为值转换失败。如果附加了调试器，您将在调试输出中看到类似的内容：

MvxBind:Error: 47,35 SetValue failed with exception - ArgumentException: Object of type 'System.String' cannot be converted to type 'System.Nullable`1[System.Decimal]'.
03-15 22:11:40.939 I/mono-stdout(25671): MvxBind:Error: 47,35 SetValue failed with exception - ArgumentException: Object of type 'System.String' cannot be converted to type 'System.Nullable`1[System.Decimal]'.
      at System.RuntimeType.CheckValue (System.Object value, System.Reflection.Binder binder, System.Globalization.CultureInfo culture, BindingFlags invokeAttr) [0x00062] in /Users/builder/data/lanes/1196/e79c13cd/source/mono/mcs/class/corlib/ReferenceSources/RuntimeType.cs:131 
  at System.Reflection.MonoMethod.ConvertValues (System.Reflection.Binder binder, System.Object[] args, System.Reflection.ParameterInfo[] pinfo, System.Globalization.CultureInfo culture, BindingFlags invokeAttr) [0x0007f] in /Users/builder/data/lanes/1196/e79c13cd/source/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:335 
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00014] in /Users/builder/data/lanes/1196/e79c13cd/source/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:283 
  at System.Reflection.MonoProperty.SetValue (System.Object obj, System.Object value, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] index, System.Globalization.CultureInfo culture) [0x0006a] in /Users/builder/data/lanes/1196/e79c13cd/source/mono/mcs/class/corlib/System.Reflection/MonoProperty.cs:445 
  at System.Reflection.PropertyInfo.SetValue (System.Object obj, System.Object value, System.Object[] index) [0x00000] in /Users/builder/data/lanes/1196/e79c13cd/source/mono/mcs/class/corlib/System.Reflection/PropertyInfo.cs:111

信息的重要部分是

'System.String'类型的对象无法转换为'System.Nullable`1 [System.Decimal]'类型。

您可以在核心库中使用值转换器来解决此问题

public class NullableValueConverter : MvxValueConverter
{
    public override object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value;
    }

    public override object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (string.IsNullOrEmpty(value?.ToString()))
            return null;

        return value;
    }
}

并将您的价值绑定为

<EditText
    local:MvxBind="Text PorcentagemDesconto, Converter=Nullable"
    android:inputType="number"
    android:layout_width="1dp"
    android:layout_weight="0.3"
    android:layout_height="wrap_content"
    android:hint="%" />

当我从EditText

1 个答案: