Xamarin.ios DialogViewController中的CommandParameter绑定_Xamarin.ios_Mvvmcross

Xamarin.ios DialogViewController中的CommandParameter绑定

xamarin.ios

Xamarin.ios DialogViewController中的CommandParameter绑定,xamarin.ios,mvvmcross,Xamarin.ios,Mvvmcross,考虑这个简单的ViewModel： public class AboutViewModel : MvxViewModel { private readonly IMvxWebBrowserTask _webBrowserTask; public AboutViewModel(IMvxWebBrowserTask webBrowserTask) { _webBrowserTask = webBrowserTask; } private MvxCommand<

考虑这个简单的

ViewModel

：

public class AboutViewModel
    : MvxViewModel
{
    private readonly IMvxWebBrowserTask _webBrowserTask;
    public AboutViewModel(IMvxWebBrowserTask webBrowserTask) { _webBrowserTask = webBrowserTask; }

    private MvxCommand<string> _showInStoreCommand;
    public ICommand ShowInStoreCommand
    {
        get
        {
            _showInStoreCommand = _showInStoreCommand ?? new MvxCommand<string>(DoShowInStoreCommand);
            return _showInStoreCommand;
        }
    }

    private void DoShowInStoreCommand(string url)
    {
        _webBrowserTask.ShowWebPage(url);
    }

    public string Wp8StoreUrl
    {
        get { return "http://windowsphone.com/s?appId=myappid"; }
    }

    public string AndroidStoreUrl
    {
        get { return "https://play.google.com/store/apps/details?id=mypackagename"; }
    }

    public string TouchStoreUrl
    {
        get { return "http://itunes.com"; }
    }
}

为什么在

DoShowInStoreCommand

的

url

参数中总是给我

null

？绑定

元素时如何使用命令参数
编辑：
我尝试了以下方法，因为Slodge在回答中所写的内容与任何扩展方法签名都不匹配，但它在尝试绑定时给了我错误：
 new StringElement("Show in App Store")
                .Bind(bindings, "SelectedCommand CommandParameter(ShowInStoreCommand, TouchStoreUrl)")

错误：
MvxBind: Error:   2.37 Problem parsing Lang binding MvxException: Must follow binding option CommandParameter with an '=' in SelectedCommand CommandParameter(ShowInStoreCommand, TouchStoreUrl)
      at Cirrious.MvvmCross.Binding.Parse.Binding.MvxBindingParser.ParseEquals (System.String block) [0x0003c] in c:\Projects\Misc\MVVMCROSS\Cirrious\Cirrious.MvvmCross.Binding\Parse\Binding\MvxBindingParser.cs:83 
  at Cirrious.MvvmCross.Binding.Parse.Binding.Swiss.MvxSwissBindingParser.ParseNextBindingDescriptionOptionInto (Cirrious.MvvmCross.Binding.Parse.Binding.MvxSerializableBindingDescription description) [0x0019a] in c:\Projects\Misc\MVVMCROSS\Cirrious\Cirrious.MvvmCross.Binding\Parse\Binding\Swiss\MvxSwissBindingParser.cs:56 
  at Cirrious.MvvmCross.Binding.Parse.Binding.Tibet.MvxTibetBindingParser.ParseNextBindingDescriptionOptionInto (Cirriou
s.MvvmCross.Binding.Parse.Binding.MvxSerializableBindingDescription description) [0x00033] in c:\Projects\Misc\MVVMCROSS\Cirrious\Cirrious.MvvmCross.Binding\Parse\Binding\Tibet\MvxTibetBindingParser.cs:49 
  at Cirrious.MvvmCross.Binding.Parse.Binding.Swiss.MvxSwissBindingParser.ParseBindingDescription (ParentIsLookingForComma parentIsLookingForComma) [0x00014] in c:\Projects\Misc\MVVMCROSS\Cirrious\Cirrious.MvvmCross.Binding\Parse\Binding\Swiss\MvxSwissBindingParser.cs:176 
  at Cirrious.MvvmCross.Binding.Parse.Binding.Swiss.MvxSwissBindingParser.ParseBindingDescription () [0x00001] in c:\Projects\Misc\MVVMCROSS\Cirrious\Cirrious.MvvmCross.Binding\Parse\Binding\Swiss\MvxSwissBindingParser.cs:159 
  at Cirrious.MvvmCross.Binding.Parse.Binding.MvxBindingParser.ParseTargetPropertyNameAndDescription () [0x0000f] in c:\Projects\Misc\MVVMCROSS\Cirrious\Cirrious.MvvmCross.Binding\Parse\Binding\MvxBindingParser.cs:72 
  at Cirrious.MvvmCross.Binding.Parse.Binding.MvxBindingParser.TryParseBindingSpecification (System
.String text, Cirrious.MvvmCross.Binding.Parse.Binding.MvxSerializableBindingSpecification& requestedBindings) [0x0001a] in c:\Projects\Misc\MVVMCROSS\Cirrious\Cirrious.MvvmCross.Binding\Parse\Binding\MvxBindingParser.cs:51 

您在中创建的绑定：
    new StringElement("Show in App Store").Bind(
                                  bindings, 
                                  e => e.SelectedCommand, 
                                  vm => vm.ShowInStoreCommand, 
                                 new MvxCommandParameterValueConverter(), ViewModel.TouchStoreUrl),

是与ViewModel上的表达式vm=>vm.ShowInStoreCommand
的绑定，但它捕获ViewModel.TouchStoreUrl的当前值
如果您想在MvvmCross中使用多重绑定，那么可以使用zida
扩展名（请参阅）来实现这一点，但是这些扩展名在流畅的表达式语法中很难访问，因此您必须使用基于字符串的语法
因此，这种绑定可以通过以下方式实现：
    new StringElement("Show in App Store").Bind(
                                  bindings, 
                                  e => e.SelectedCommand, 
                                  "CommandParameter(ShowInStoreCommand, TouchStoreUrl)")

    new StringElement("Show in App Store").Bind(
                                  bindings, 
                                  e => e.SelectedCommand, 
                                  "CommandParameter(ShowInStoreCommand, TouchStoreUrl)")