MVVCross：传递一个枚举值作为Android的一个CommandParameter [英] MVVCross: Pass an enum value as a CommandParameter for Android

问题描述

我想传递一个枚举值作为CommandParameter。
我的枚举定义为：

 公共枚举MyEnum
{
   一，
   二
}
 

在我AXML我有：

 地方：MvxBind =点击MyCommand，CommandParameter = MyEnum.One
...
本地：MvxBind =点击MyCommand，CommandParameter = MyEnum.Two
 

和MyCommand在我的ViewModel定义为

 公共IMvxCommand MyCommand
{
  {返回新MvxCommand＆LT; MyEnum＆GT;（MyFunction的）; }
}私人无效MyFunction的（MyEnum p_enumParam）
{
  开关（p_enumParam）
  {
      案例MyEnum.One：
          doSomething1（）;
          打破;
      案例MyEnum.Two：
          了doSomething2（）;
          打破;
  }
}
 

当我运行它，我得到的错误System.InvalidCastException：不能从源类型到目标类型强制转换

显然，因为它不能施放 MyEnum.One 和 MyEnum.Two 来的MyEnum类型。所以，我怎么能说服它的 MyEnum.One 和 MyEnum.Two 是 MyEnum <的/ code>键入<？/ p>

谢谢，
巴氏

解决方案

MvvmCross不能从绑定声明猜枚举类型 - 所以它不能执行此结合

在这个最简单的路线可能是解决这一使用字符串！而非 - 然后你就需要使用 Enum.Parse 从字符串到您的视图模型的枚举。

---

另一种方法是，您还可以实现一个枚举解析ValueConverter刚刚解析字符串 - 例如你可以立足于<一个href=\"https://github.com/MvvmCross/MvvmCross/blob/v3.1/Cirrious/Cirrious.MvvmCross.Binding/ValueConverters/MvxCommandParameterValueConverter.cs\" rel=\"nofollow\">https://github.com/MvvmCross/MvvmCross/blob/v3.1/Cirrious/Cirrious.MvvmCross.Binding/ValueConverters/MvxCommandParameterValueConverter.cs - 您可以添加 Enum.Parse 来此创建：

 公共类MyEnumCommandValueConverter
    ：MvxValueConverter＆LT; ICommand的，ICommand的＆GT;
{
    保护覆盖的ICommand转换（ICommand的价值，System.Type的TARGETTYPE，对象参数，System.Globalization.CultureInfo文化）
    {
        返回新MvxWrappingCommand（值，Enum.Parse（typeof运算（MyEnum），parameter.ToString（）））;
    }
}
 

然后，您可以使用绑定嵌套 - 使用类似：

 地方：MvxBind =点击MyEnumCommand（MyCommand，'两'）
 

I want to pass an enum value as a CommandParameter. My enum is defined as:

public enum MyEnum
{
   One,
   Two
}

And in my axml I have:

local:MvxBind="Click MyCommand, CommandParameter=MyEnum.One"
...
local:MvxBind="Click MyCommand, CommandParameter=MyEnum.Two"

and MyCommand is defined in my ViewModel as

public IMvxCommand MyCommand
{
  get { return new MvxCommand<MyEnum>(myfunction); }
}

private void myfunction(MyEnum p_enumParam)
{
  switch (p_enumParam)
  {
      case MyEnum.One:
          doSomething1();
          break;
      case MyEnum.Two:
          doSomething2();
          break;
  }
}

When I run it, I get the error "System.InvalidCastException: Cannot cast from source type to destination type."

Obviously, because it cannot cast MyEnum.One and MyEnum.Two to the MyEnum type. So how can I convince it that MyEnum.One and MyEnum.Two are of MyEnum type?

Thanks, Pap

解决方案

MvvmCross can't guess the type of enum from the binding statement - so it can't perform this binding.

The easiest route on this is probably to workaround this using strings instead - and you will then need to use Enum.Parse from the string to the enum in your ViewModel.

---

An alternative is that you could also implement an enum parsing ValueConverter which just parsed the string - e.g. you could base on https://github.com/MvvmCross/MvvmCross/blob/v3.1/Cirrious/Cirrious.MvvmCross.Binding/ValueConverters/MvxCommandParameterValueConverter.cs - you could add Enum.Parse to this to create:

public class MyEnumCommandValueConverter
    : MvxValueConverter<ICommand, ICommand>
{
    protected override ICommand Convert(ICommand value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return new MvxWrappingCommand(value, Enum.Parse(typeof(MyEnum), parameter.ToString()));
    }
}

You could then bind using nesting - using something like:

local:MvxBind="Click MyEnumCommand(MyCommand, 'Two')"

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