[英]Cast Binding Path so it recognises ViewModel property at Design-Time
Ok this is more of an annoyance than a problem.好吧,这比问题更令人烦恼。 There is no error
没有错误
Page页
<ContentPage
...
x:Name="This"
//hack to have typed xaml at design-time
BindingContext="{Binding Source={x:Static viewModels:ViewModelLocator.ChooseTargetLocationVm}}"
SubView子视图
<views:ProductStandardView
...
BindingContext="{Binding Product}">
<Grid.Triggers>
<DataTrigger
Binding="{Binding Path=BindingContext.IsVacate, Source={x:Reference This}}"
TargetType="Grid"
Value="true">
<Setter Property="BackgroundColor" Value="{StaticResource WarningColor}" />
</DataTrigger>
</Grid.Triggers>
When Binding to BindingContext
from the Source Reference of This
, i get a XAML "warning"当从
This
的源引用绑定到BindingContext
,我收到 XAML“警告”
Cannot resolve property 'IsVacate' in data context of type 'object'
无法在“对象”类型的数据上下文中解析属性“IsVacate”
Binding="{Binding Path=BindingContext.IsVacate, Source={x:Reference This}}"
Obviously the BindingContext is an object and untyped.显然BindingContext是一个对象并且是无类型的。 However the above code compiles and works
但是上面的代码编译并工作
What i want to do is cast it, firstly because i have OCD, however mainly because its easy to spot real problems on the IDE page channel bar我想做的是投射它,首先是因为我有强迫症,但主要是因为它很容易在 IDE 页面通道栏上发现真正的问题
The following seems logical but doesn't work以下似乎合乎逻辑但不起作用
Binding="{Binding Path=BindingContext.(viewModels:ChooseTargetLocationVm.IsVacate),
Source={x:Reference This}}"
In the output i get在输出中我得到
[0:] Binding: '(
viewModels:ChooseTargetLocationVm
' property not found on 'Inhouse.Mobile.Standard.ViewModels.ChooseTargetLocationVm
', target property: 'Inhouse.Mobile.Standard.Views.ProductStandardView.Bound
'[0:] 绑定:'(
viewModels:ChooseTargetLocationVm
'属性未在'Inhouse.Mobile.Standard.ViewModels.ChooseTargetLocationVm
'上找到,目标属性:'Inhouse.Mobile.Standard.Views.ProductStandardView.Bound
'
I understand the error, yet how else would i cast?我明白这个错误,但我还能如何施展?
And just for stupidity, obviously the following wont compile只是为了愚蠢,显然以下不会编译
Binding="{Binding Path=((viewModels:ChooseTargetLocationVm)BindingContext).IsVacate, Source={x:Reference This}}"
So is there a way to cast a BindingContext to a ViewModel so any SubProperty references are typed at design time?那么有没有办法将BindingContext转换为ViewModel,以便在设计时输入任何SubProperty引用?
Update更新
This is relevant for inside a DataTemplate
or in this case when the control has its own BindingContext
which is why i need to use the Source={x:Reference This}
to target the page.这与
DataTemplate
内部相关,或者在这种情况下,当控件具有自己的BindingContext
,这就是为什么我需要使用Source={x:Reference This}
来定位页面的原因。
Note : <ContentPage.BindingContext>
doesn't work for me as i'm using prism and unity and it doesn't seem to play with well a default constructor on initial tests, though i might play around with this some more注意:
<ContentPage.BindingContext>
对我不起作用,因为我正在使用棱镜和统一,并且它似乎在初始测试中与默认构造函数一起使用效果不佳,尽管我可能会更多地使用它
You can extend ContentPage
to create a generic type - that supports type parameter for view-model - which in turn can be used in Binding
markup extension.您可以扩展
ContentPage
以创建通用类型 - 支持视图模型的类型参数 - 反过来可以在Binding
标记扩展中使用。
Although it may not give you intellisense like support - but should definitely remove the warning for you.虽然它可能不会为您提供类似智能感知的支持 - 但绝对应该为您删除警告。
For eg:例如:
/// <summary>
/// Create a base page with generic support
/// </summary>
public class ContentPage<T> : ContentPage
{
/// <summary>
/// This property basically type-casts the BindingContext to expected view-model type
/// </summary>
/// <value>The view model.</value>
public T ViewModel { get { return (BindingContext != null) ? (T)BindingContext : default(T); } }
/// <summary>
/// Ensure ViewModel property change is raised when BindingContext changes
/// </summary>
protected override void OnBindingContextChanged()
{
base.OnBindingContextChanged();
OnPropertyChanged(nameof(ViewModel));
}
}
<?xml version="1.0" encoding="utf-8"?>
<l:ContentPage
...
xmlns:l="clr-namespace:SampleApp"
x:TypeArguments="l:ThisPageViewModel"
x:Name="This"
x:Class="SampleApp.SampleAppPage">
...
<Label Text="{Binding ViewModel.PropA, Source={x:Reference This}}" />
...
</l:ContentPage>
Code-behind代码隐藏
public partial class SampleAppPage : ContentPage<ThisPageViewModel>
{
public SampleAppPage()
{
InitializeComponent();
BindingContext = new ThisPageViewModel();
}
}
View model查看模型
/// <summary>
/// Just a sample viewmodel with properties
/// </summary>
public class ThisPageViewModel
{
public string PropA { get; } = "PropA";
public string PropB { get; } = "PropB";
public string PropC { get; } = "PropC";
public string[] Items { get; } = new[] { "1", "2", "3" };
}
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