Question

是否可以将UIViewController的Title绑定到ViewModel字符串属性？它似乎永远不会更新。作为一个副作用，如果你没有在绑定之前将标题设置为某个东西，那么当set.Apply（）被调用时，Mvvmcross代码会出现崩溃。

UIViewController没有.xib，我不确定这是否是问题的一部分。

public override void ViewDidLoad()
{
  base.ViewDidLoad();

  var set = this.CreateBindingSet<HomeView, HomeViewModel>();
  set.Bind(Title).To(vm => vm.ProjectName);
  set.Apply();
}

这是堆栈跟踪

2014-02-05 17：09：35.740 TerraFlex [9145：907] 02-05-2014 17：09：35：7403：1：[Info] HomeView已加载线程开始：＃12 2014-02-05 17：09：36.219 TerraFlex [9145：907] 02-05-2014 17：09：36：2190：1：[致命]发生了严重错误，应用程序已关闭 2014-02-05 17：09：36.250 TerraFlex [9145：907] 02-05-2014 17：09：36：2497：1：[致命]日期：5/02/2014 5:09:36 PM，[例外] ] 致命消息：对象引用未设置为对象的实例 Stack：在c：\ Projects \ Misc \ MVVMCROSS \ Cirrious \ Cirrious中的Cirrious.MvvmCross.Binding.Bindings.Target.Construction.MvxTargetBindingFactoryRegistry.TryCreateSpecificFactoryBinding（System.Object target，System.String targetName，IMvxTargetBinding＆amp; binding）[0x00001]。 MvvmCross.Binding \绑定\目标\建筑\ MvxTargetBindingFactoryRegistry.cs：69 在Cirrious.MvvmCross.Binding.Bindings.Target.Construction.MvxTargetBindingFactoryRegistry.CreateBinding（System.Object target，System.String targetName）[0x00001]在c：\ Projects \ Misc \ MVVMCROSS \ Cirrious \ Cirrious.MvvmCross.Binding \ Bindings \目标\建筑\ MvxTargetBindingFactoryRegistry.cs：22 在Cirrious.MvvmCross.Binding.Bindings.MvxFullBinding.CreateTargetBinding（System.Object target）[0x00003]在c：\ Projects \ Misc \ MVVMCROSS \ Cirrious \ Cirrious.MvvmCross.Binding \ Bindings \ MvxFullBinding.cs：135 在Cirrious.MvvmCross.Binding.Bindings.MvxFullBinding..ctor（Cirrious.MvvmCross.Binding.MvxBindingRequest bindingRequest）[0x00014]在c：\ Projects \ Misc \ MVVMCROSS \ Cirrious \ Cirrious.MvvmCross.Binding \ Bindings \ MvxFullBinding.cs： 60 at Cirrious.MvvmCross.Binding.Binders.MvxFromTextBinder.BindSingle（Cirrious.MvvmCross.Binding.MvxBindingRequest bindingRequest）[0x00001]在c：\ Projects \ Misc \ MVVMCROSS \ Cirrious \ Cirrious.MvvmCross.Binding \ Binders \ MvxFromTextBinder.cs：55 at Cirrious.MvvmCross.Binding.Binders.MvxFromTextBinder +＆lt;＆gt; c_ DisplayClass1.b _0（Cirrious.MvvmCross.Bindings.Bindings.MvxBindingDescription description）[0x00000]在c：\ Projects \ Misc \ MVVMCROSS \ Cirrious \ Cirrious.MvvmCross.Binding \装订\ MvxFromTextBinder.cs：37 在System.Linq.Enumerable + c__Iterator10 2[Cirrious.MvvmCross.Binding.Bindings.MvxBindingDescription,Cirrious.MvvmCross.Binding.Bindings.IMvxUpdateableBinding].MoveNext () [0x00000] in <filename unknown>:0 at Cirrious.MvvmCross.Binding.BindingContext.MvxBindingContextOwnerExtensions.AddBindings (IMvxBindingContextOwner view, IEnumerable 1个绑定，System.Object clearKey）[0x00028]在c：\ Projects \ Misc \ MVVMCROSS \ Cirrious \ Cirrious.MvvmCross.Binding \ BindingContext \ MvxBindingContextOwnerExtensions.cs：69 在Cirrious.MvvmCross.Binding.BindingContext.MvxBindingContextOwnerExtensions.AddBindings（IMvxBindingContextOwner视图，System.Object目标，IEnumerable 1 bindingDescriptions, System.Object clearKey) [0x00019] in c:\Projects\Misc\MVVMCROSS\Cirrious\Cirrious.MvvmCross.Binding\BindingContext\MvxBindingContextOwnerExtensions.cs:90 at Cirrious.MvvmCross.Binding.BindingContext.MvxBindingContextOwnerExtensions.AddBinding (IMvxBindingContextOwner view, System.Object target, Cirrious.MvvmCross.Binding.Bindings.MvxBindingDescription bindingDescription, System.Object clearKey) [0x0000e] in c:\Projects\Misc\MVVMCROSS\Cirrious\Cirrious.MvvmCross.Binding\BindingContext\MvxBindingContextOwnerExtensions.cs:83 at Cirrious.MvvmCross.Binding.BindingContext.MvxBaseFluentBindingDescription 1 [System.String] .Apply（）[0x00000] in：0 在Cirrious.MvvmCross.Binding.BindingContext.MvxFluentBindingDescriptionSet`2 [Trimble.TFM.FieldApp.HomeView，Trimble.TFM.FieldApp.Common.HomeViewModel] .Apply（）[0x00000] in：0

谢谢，乔恩

Answer 1

Fluent绑定使用如下代码：

 set
    .Bind(<target object for bind>)
    .For(<property on target object>) // leave this out to use the "default binding property for the target object"
    .To(<property/expression on source object>)
    .WithConversion(<converter>, <converter parameter>) // optional
    .OneWay() // optional - also: OneWayToSource(), TwoWay() or OneTime()
    .FallbackValue(<value to use for UnsetValue>(); // optional

您可以在以下网址了解更多相关信息：

https://github.com/MvvmCross/MvvmCross/wiki/Databinding#wiki-fluent

你的绑定是：

set.Bind(Title).To(vm => vm.ProjectName);

所以你有约束力：

.Bind(Title) - 当前Title对象中的任何内容（通常为null）
对于该对象的默认绑定属性 - 取决于对象类型 - 请参阅https://github.com/MvvmCross/MvvmCross/blob/v3.1/Cirrious/Cirrious.MvvmCross.Binding.Touch/MvxTouchBindingBuilder.cs#L104以获取基本列表
到您的DataContext上的ProjectName（通常是您的ViewModel）

我想你想要的是：

set.Bind(this).For(v => v.Title).To(vm => vm.ProjectName);

我认为你也可以这样做：

set.Bind().For(v => v.Title).To(vm => vm.ProjectName);

话虽如此，Mvx堆栈实际上不应该有null目标和属性 - 它不习惯 - 因此我会将此作为一个问题添加到调查并添加回归测试TryCreateSpecificFactoryBinding无法处理null的原因。

Mvvmcross（iOS）绑定UIViewController的标题

1 个答案: