Xamarin-将命令绑定到用户控件内对象的属性 [英] Xamarin - Binding Command to property of object inside User Control
问题描述
几天前，我已经开始学习XAML，但是在解决这个问题时遇到了麻烦.
I have began learning XAML a few days ago and I have a trouble with wrapping my head around this problem.
在Xamarin Forms中，我想创建一个用户控件，其中将包含标签和按钮，并能够将命令绑定到使用我的用户控件的另一个页面中的XAML中的用户控件.
In Xamarin Forms, I want to create a user control which will contain a label and a button and be able to bind a command to usercontrol in XAML from another page which uses my user control.
我目前遇到异常:
Xamarin.Forms.Xaml.XamlParseException:'位置8:24.无法分配属性"Test1":属性不存在或不可分配，或者值与属性之间的类型不匹配
Xamarin.Forms.Xaml.XamlParseException: 'Position 8:24. Cannot assign property "Test1": Property does not exists, or is not assignable, or mismatching type between value and property'
这是我目前想开始使用的精简版本.
Here is a dumbed down version of it I am currently trying to get to work.
我的自定义控件XAML
My Custom Control XAML
<?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="App3.Controls.Control1">
<StackLayout>
<Button Command="{Binding Test1}" Text="Test"/>
</StackLayout>
</ContentView>
使用我的自定义控件XAML进行控制
Control using my Custom Control XAML
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:App3"
xmlns:controls="clr-namespace:App3.Controls"
x:Class="App3.MainPage">
<controls:Control1 Test1="{Binding Test2}" />
</ContentPage>
隐藏了我的自定义控制代码
My Custom Control Codebehind
using System.Windows.Input;
using Xamarin.Forms;
namespace App3.Controls
{
public partial class Control1 : ContentView
{
private static readonly BindableProperty controlProperty = BindableProperty.Create("Test1", typeof(ICommand), typeof(Control1), null);
public Control1()
{
InitializeComponent();
}
public ICommand Test1
{
get
{
return (ICommand)GetValue(controlProperty);
}
set
{
SetValue(controlProperty, value);
}
}
}
}
使用自定义控件"查看页面模型
View Model of page using Custom Control
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows.Input;
using Xamarin.Forms;
namespace App3
{
public class MainPageViewModel : INotifyPropertyChanged
{
public MainPageViewModel()
{
this.Test2 = new Command(test);
}
public void test()
{
Application.Current.MainPage.DisplayAlert("it works", "it works", "it works");
}
public ICommand Test2
{
get; set;
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
}
推荐答案
如果要从Xaml检测到可绑定的BindableProperty，可以遵循以下命名约定:
There are a few naming convention to follow if you want your BindableProperty detected, and bindable, from Xaml:
创建标识符字段时，请使用注册时属性的名称以及后缀"Property"来命名此字段.此字段是您依赖项属性的标识符，以后将用作您将在包装器中进行的SetValue和GetValue调用的输入，通过您自己的代码通过对该属性的任何其他代码访问，或者通过任何外部代码访问，您允许，通过属性系统，还可以通过XAML处理器.
When you create the identifier field, name this field by the name of the property as you registered it, plus the suffix Property. This field is your identifier for the dependency property, and it will be used later as an input for the SetValue and GetValue calls you will make in the wrappers, by any other code access to the property by your own code, by any external code access you allow, by the property system, and potentially by XAML processors.
和
将DependencyProperty标识符定义为所有者类型上的公共静态只读字段.
Define a DependencyProperty identifier as a public static readonly field on the owner type.
(这是DependencyProperty的文档，但是在这种情况下，它非常适用于BindableProperties.请参见
(this is the documentation for DependencyProperty, but it applies to BindableProperties quite well in this case. See https://msdn.microsoft.com/en-us/library/ms753358(v=vs.110).aspx)
您可以通过替换来修复代码
You can fix your code by replacing
private static readonly BindableProperty controlProperty = BindableProperty.Create("Test1", typeof(ICommand), typeof(Control1), null);
public ICommand Test1
{
get { return (ICommand)GetValue(controlProperty); }
set { SetValue(controlProperty, value); }
}
作者
public static readonly BindableProperty Test1Property = BindableProperty.Create("Test1", typeof(ICommand), typeof(Control1), null);
public ICommand Test1
{
get { return (ICommand)GetValue(Test1Property); }
set { SetValue(Test1Property, value); }
}
这应该可以防止属性检测问题.
That should prevent the property detection issue.
为使您的全部内容正常工作，Button命令绑定应将其源设置为控件本身，并且应将MainPageViewModel设置为BindingContext作为MainPage.
to get your full stuff working, the Button command binding should have it's source set to the control itself, and you should set your MainPageViewModel as BindingContext for MainPage.
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