我正在尝试在使用 Catel MVVM 框架实现的项目上使用编译绑定(bind)(应该没关系)。然而,在生成的代码中,我得到编译器错误,因为我的 ViewModel 没有实现通常由 DependencyObjects 公开的某些函数:
CS1061 'MainViewModel' does not contain a definition for 'RegisterPropertyChangedCallback' and no extension method 'RegisterPropertyChangedCallback' accepting a first argument of type 'MainViewModel' could be found (are you missing a using directive or an assembly reference?)
还:
CS0039 Cannot convert type 'Windows.UI.Xaml.DependencyObject' to 'CatelCompiledBindingTest.ViewModels.MainViewModel' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion
x:Bind
引发错误的编译器生成的代码如下:public void DependencyPropertyChanged_VM_Visible(global::Windows.UI.Xaml.DependencyObject sender, global::Windows.UI.Xaml.DependencyProperty prop)
{
MainView_obj1_Bindings bindings = TryGetBindingObject();
if (bindings != null)
{
global::CatelCompiledBindingTest.ViewModels.MainViewModel obj = sender as global::CatelCompiledBindingTest.ViewModels.MainViewModel;
if (obj != null)
{
bindings.Update_VM_Visible(obj.Visible, DATA_CHANGED);
}
}
}
private global::CatelCompiledBindingTest.ViewModels.MainViewModel cache_VM = null;
private long tokenDPC_VM_Visible = 0;
public void UpdateChildListeners_VM(global::CatelCompiledBindingTest.ViewModels.MainViewModel obj)
{
if (obj != cache_VM)
{
if (cache_VM != null)
{
((global::System.ComponentModel.INotifyPropertyChanged)cache_VM).PropertyChanged -= PropertyChanged_VM;
cache_VM.UnregisterPropertyChangedCallback(global::CatelCompiledBindingTest.ViewModels.MainViewModel.VisibleProperty, tokenDPC_VM_Visible);
cache_VM = null;
}
if (obj != null)
{
cache_VM = obj;
((global::System.ComponentModel.INotifyPropertyChanged)obj).PropertyChanged += PropertyChanged_VM;
tokenDPC_VM_Visible = obj.RegisterPropertyChangedCallback(global::CatelCompiledBindingTest.ViewModels.MainViewModel.VisibleProperty, DependencyPropertyChanged_VM_Visible);
}
}
}
MainViewModel 相当简单(不包括 Catel 样板代码):
public class MainViewModel : ViewModelBase
{
public MainViewModel()
{
ToggleVisibility = new Command(OnToggleVisibilityExecute);
AddText = new Command(OnAddTextExecute);
SomeText = "";
}
//ViewModel properties
public string SomeText
{
get { return GetValue<string>(SometextProperty); }
set { SetValue(SometextProperty, value); }
}
public bool Visible
{
get { return GetValue<bool>(VisibleProperty); }
set { SetValue(VisibleProperty, value); }
}
//ViewModel Commands
public Command ToggleVisibility { get; private set; }
public void OnToggleVisibilityExecute()
{
Visible = !Visible;
}
public Command AddText { get; private set; }
public void OnAddTextExecute()
{
SomeText += "Random text! ";
}
}
View 如下:
<controls:Page
x:Class="CatelCompiledBindingTest.Views.MainView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:CatelCompiledBindingTest.Views"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:controls="using:Catel.Windows.Controls"
xmlns:converters="using:Catel.MVVM.Converters"
mc:Ignorable="d"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Page.Resources>
<converters:BooleanToCollapsingVisibilityConverter x:Key="BooleanToVisibilityConverter"/>
</Page.Resources>
<Grid>
<Grid.KeyboardAccelerators>
<KeyboardAccelerator Invoked="{x:Bind VM.OnToggleVisibilityExecute}" Key="T" Modifiers="Control"/>
<KeyboardAccelerator Invoked="{x:Bind VM.OnAddTextExecute}" Key="Add" Modifiers="Control"/>
</Grid.KeyboardAccelerators>
<Border Width="500" Height="500" Visibility="{x:Bind VM.Visible, Mode=OneWay}" Background="SlateGray">
<TextBlock Style="{ThemeResource HeaderTextBlockStyle}" Text="{x:Bind VM.SomeText, Mode=OneWay}"/>
</Border>
</Grid>
</controls:Page>
使用以下代码隐藏能够使用已编译的绑定(bind):
public sealed partial class MainView : Page
{
public MainView()
{
this.InitializeComponent();
VM = DataContext as MainViewModel;
}
public MainViewModel VM { get; set; }
}
现在的问题是:为什么编译器假定 MainViewModel 的类型为
DependencyObject
在编译器生成的DependencyPropertyChanged_VM_Visible
?根据Data Binding in Depth ViewModel 只需要实现 IPropertyChanged
它确实如此。我该如何解决这个问题(除了再次求助
{Binding}
)?我需要在 ViewModel 中包含哪些命名空间才能使编译的 Bindings 工作?
最佳答案
它假定它是一个依赖属性,因为 VM
属性在 View MainView
上声明.您应该定义 VM
属性作为依赖属性,因此可以绑定(bind)到(所以不是属性的值/类型,而是属性本身)。
关于c# - 做编译绑定(bind)(x :Bind) require the ViewModel to derive from DependencyObject?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51881013/