问题
At work I have several pages, each with buttons in the same places, and with the same properties. Each page also has minor differences. To that end, we created a userControl Template and put all the buttons in it, then applied that user control to all the pages. However, now it's rather hard to access the buttons and modify them from each page's xaml, because they are inside a UserControl on the page..... How do I elegantly access the buttons from each page?
What I've tried:
Currently, we bind to a bunch of dependency properties. I don't like this option because I have a lot of buttons, and need to control a lot of properties on those buttons. The result is hundreds of dependency properties, and a real mess to wade through when we need to change something.
Another method is to use styles. I like this method generally, but because these buttons are inside another control it becomes difficult to modify them, and the template would only be exactly right for one button, at one time.
Adam Kemp posted about letting the user just insert their own button here, and this is the method I'm currently trying to impliment / modify. Unfortunately, I don't have access to Xamarin.
Although the template is inserted when the code runs, the template is not updating the button correctly. If I put a breakpoint in the MyButton Setter, I can see that value is actually an empty button, rather than the one I assigned in my main window. How do I fix this?
Here's some simplified Code:
My Template UserControl's xaml:
<UserControl x:Class="TemplateCode.Template"
x:Name="TemplatePage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="350"
d:DesignWidth="525"
DataContext="{Binding RelativeSource={RelativeSource Self}}"
Background="DarkGray">
<Grid>
<Button x:Name="_button" Width="200" Height="100" Content="Template Button"/>
</Grid>
</UserControl>
My Template UserControl's Code Behind:
using System.Windows.Controls;
namespace TemplateCode
{
public partial class Template : UserControl
{
public static Button DefaultButton;
public Template()
{
InitializeComponent();
}
public Button MyButton
{
get
{
return _button;
}
set
{
_button = value; //I get here, but value is a blank button?!
// Eventually, I'd like to do something like:
// Foreach (property in value)
// {
// If( value.property != DefaultButton.property) )
// {
// _button.property = value.property;
// }
// }
// This way users only have to update some of the properties
}
}
}
}
And now the application where I want to use it:
<Window x:Class="TemplateCode.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
xmlns:templateCode="clr-namespace:TemplateCode"
Title="MainWindow"
Height="350"
Width="525"
Background="LimeGreen"
DataContext="{Binding RelativeSource={RelativeSource Self}}" >
<Grid>
<templateCode:Template>
<templateCode:Template.MyButton>
<Button Background="Yellow"
Content="Actual Button"
Width="200"
Height="100"/>
</templateCode:Template.MyButton>
</templateCode:Template>
</Grid>
</Window>
And Now the Code Behind:
Using System.Windows;
Namespace TemplateCode
{
Public partial class MainWindow : Window
{
Public MainWindow()
{
InitializeComponent();
}
}
}
Edit: While I want to remove unnecessary dependency properties in the template userControl, I'd still like to set bindings on the button's properties from the XAML.
回答1:
rather than use many dependency properties, prefer style approach. Style contains every property available for a Button control.
I would create a DependencyProperty for each button style in UserControl.
public partial class TemplateUserControl : UserControl
{
public TemplateUserControl()
{
InitializeComponent();
}
public static readonly DependencyProperty FirstButtonStyleProperty =
DependencyProperty.Register("FirstButtonStyle", typeof (Style), typeof (TemplateUserControl));
public Style FirstButtonStyle
{
get { return (Style)GetValue(FirstButtonStyleProperty); }
set { SetValue(FirstButtonStyleProperty, value); }
}
public static readonly DependencyProperty SecondButtonStyleProperty =
DependencyProperty.Register("SecondButtonStyle", typeof (Style), typeof (TemplateUserControl));
public Style SecondButtonStyle
{
get { return (Style)GetValue(SecondButtonStyleProperty); }
set { SetValue(SecondButtonStyleProperty, value); }
}
}
and then modify xaml for buttons to pick these styles:
<UserControl x:Class="MyApp.TemplateUserControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="200" d:DesignWidth="300"
Background="DarkGray">
<StackPanel>
<Button x:Name="_button" Width="200" Height="100"
Style="{Binding Path=FirstButtonStyle, RelativeSource={RelativeSource AncestorType=UserControl}}"/>
<Button x:Name="_button2" Width="200" Height="100"
Style="{Binding Path=SecondButtonStyle, RelativeSource={RelativeSource AncestorType=UserControl}}"/>
</StackPanel>
</UserControl>
now when buttons have to be customized, that can achieved by custom styles:
<StackPanel>
<StackPanel.Resources>
<!--common theme properties-->
<Style TargetType="Button" x:Key="TemplateButtonBase">
<Setter Property="FontSize" Value="18"/>
<Setter Property="Foreground" Value="Blue"/>
</Style>
<!--unique settings of the 1st button-->
<!--uses common base style-->
<Style TargetType="Button" x:Key="BFirst" BasedOn="{StaticResource TemplateButtonBase}">
<Setter Property="Content" Value="1st"/>
</Style>
<Style TargetType="Button" x:Key="BSecond" BasedOn="{StaticResource TemplateButtonBase}">
<Setter Property="Content" Value="2nd"/>
</Style>
</StackPanel.Resources>
<myApp:TemplateUserControl FirstButtonStyle="{StaticResource BFirst}"
SecondButtonStyle="{StaticResource BSecond}"/>
</StackPanel>
回答2:
You could register a Dependency Property Button on your UserControland handle the initialization in its PropertyChangedCallback.
Template.xaml.cs
using System;
using System.Windows;
using System.Windows.Controls;
using System.Collections.Generic;
using System.Windows.Markup.Primitives;
namespace TemplateCode
{
public partial class Template : UserControl
{
public Template()
{
InitializeComponent();
}
public static readonly DependencyProperty ButtonProperty =
DependencyProperty.Register("Button", typeof(Button), typeof(Template),
new UIPropertyMetadata(new PropertyChangedCallback(ButtonChangedCallback)));
public Button Button
{
get { return (Button)GetValue(ButtonProperty); }
set { SetValue(ButtonProperty, value); }
}
public static List<DependencyProperty> GetDependencyProperties(Object element)
{
List<DependencyProperty> properties = new List<DependencyProperty>();
MarkupObject markupObject = MarkupWriter.GetMarkupObjectFor(element);
if (markupObject != null)
{
foreach (MarkupProperty mp in markupObject.Properties)
{
if (mp.DependencyProperty != null)
{
properties.Add(mp.DependencyProperty);
}
}
}
return properties;
}
private static void ButtonChangedCallback(object sender, DependencyPropertyChangedEventArgs args)
{
// Get button defined by user in MainWindow
Button userButton = (Button)args.NewValue;
// Get template button in UserControl
UserControl template = (UserControl)sender;
Button templateButton = (Button)template.FindName("button");
// Get userButton props and change templateButton accordingly
List<DependencyProperty> properties = GetDependencyProperties(userButton);
foreach(DependencyProperty property in properties)
{
if (templateButton.GetValue(property) != userButton.GetValue(property))
{
templateButton.SetValue(property, userButton.GetValue(property));
}
}
}
}
}
Template.xaml
UserControl DataContext is inherited from parent, no need not to set it explicitly
<UserControl x:Class="TemplateCode.Template"
x:Name="TemplatePage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="350"
d:DesignWidth="525"
Background="DarkGray">
<Grid>
<Button x:Name="button" Width="200" Height="100" Content="Template Button"/>
</Grid>
</UserControl>
MainWindow.xaml
You were setting Button.Content instead of Button
<Window x:Class="TemplateCode.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
xmlns:templateCode="clr-namespace:TemplateCode"
Title="MainWindow"
Height="350"
Width="525">
<Window.Resources>
<Button x:Key="UserButton"
Background="Yellow"
Content="Actual Button"
Width="200"
Height="100"
/>
</Window.Resources>
<Grid>
<templateCode:Template Button="{StaticResource UserButton}"/>
</Grid>
</Window>
EDIT - Binding Button.Content
3 ways to do this:
1. Dependency Properties
By far the best method. Creating UserControl DP's for every property on the Button is certainly overkill, but for those you want bound to the ViewModel / MainWindow DataContext it makes sense.
Adding in Template.xaml.cs
public static readonly DependencyProperty TextProperty =
DependencyProperty.Register("Text", typeof(string), typeof(Template));
public string Text
{
get { return (string)GetValue(TextProperty); }
set { SetValue(TextProperty, value); }
}
Template.xaml
<UserControl x:Class="TemplateCode.Template"
...
DataContext="{Binding RelativeSource={RelativeSource Self}}">
<Grid>
<Button x:Name="button" Width="200" Height="100" Content="{Binding Text}"/>
</Grid>
</UserControl>
MainWindow.xaml
<Window.Resources>
<Button x:Key="UserButton"
Background="Yellow"
Width="200"
Height="100"
/>
</Window.Resources>
<Grid>
<templateCode:Template
Button="{StaticResource UserButton}"
Text="{Binding DataContext.Txt,
RelativeSource={RelativeSource AncestorType={x:Type Window}}}"/>
</Grid>
Or
<Window.Resources>
<Button x:Key="UserButton"
Background="Yellow"
Content="Actual Button"
Width="200"
Height="100"
/>
</Window.Resources>
<Grid>
<templateCode:Template
Button="{StaticResource UserButton}"/>
</Grid>
Value precedence: UserButton Content > DP Text, so setting the Content in Resources wins.
2. Creating the Button in your ViewModel
MVVM purists won't like this, but you could use the Binding mark up instead of StaticResource.
MainWindow.xaml
<Grid>
<templateCode:Template
Button="{Binding DataContext.UserButton,
RelativeSource={RelativeSource AncestorType={x:Type Window}}}"/>
</Grid>
3. Setting the binding in code
As you already noticed, a ViewModel prop (e.g. Txt) can't be referenced in Resources because of the order everything is initialized. You can still do it in code later, but it gets a bit messy with the error to prove.
System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Window', AncestorLevel='1''. BindingExpression:Path=DataContext.Txt; DataItem=null; target element is 'Button' (Name=''); target property is 'Content' (type 'Object')
Note you need to define the full path on the Content property (setting DataContext on parent won't do).
MainWindow.xaml
<Window.Resources>
<Button x:Key="UserButton"
Background="Yellow"
Width="200"
Height="100"
Content="{Binding DataContext.Txt,
RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
/>
</Window.Resources>
<Grid>
<templateCode:Template Button="{StaticResource UserButton}"/>
</Grid>
Template.xaml.cs
private static void ButtonChangedCallback(object sender, DependencyPropertyChangedEventArgs args)
{
// Get button defined by user in MainWindow
Button userButton = (Button)args.NewValue;
// Get template button in UserControl
UserControl template = (UserControl)sender;
Button templateButton = (Button)template.FindName("button");
// Get userButton props and change templateButton accordingly
List<DependencyProperty> properties = GetDependencyProperties(userButton);
foreach (DependencyProperty property in properties)
{
if (templateButton.GetValue(property) != userButton.GetValue(property))
templateButton.SetValue(property, userButton.GetValue(property));
}
// Set Content binding
BindingExpression bindingExpression = userButton.GetBindingExpression(Button.ContentProperty);
if (bindingExpression != null)
templateButton.SetBinding(Button.ContentProperty, bindingExpression.ParentBinding);
}
回答3:
If you can group your changes to your buttons to one or multiple properties on your datacontext, you could work with DataTriggers:
<Button x:Name="TestButton">
<Button.Style>
<Style>
<Style.Triggers>
<DataTrigger Binding="{Binding IsButtonEnabled}" Value="True">
<Setter TargetName="TestButton" Property="Background" Value="Red" />
</DataTrigger>
</Style.Triggers>
</Style>
</Button.Style>
</Button>
You can even use multiple conditions with MultiDataTriggers.
回答4:
The main problem is that Template components are initialized before mainwindow components.I mean all properties of the button in mainwindow are set after the button in template class is initialized. Therefore, as you said value sets to null. All I want to say is about sequence of initializing objects.If you make a trick such a way as follows ;
public partial class Template : UserControl
{
private Button _btn ;
public Template()
{
}
public Button MyButton
{
get
{
return _button;
}
set
{
_btn = value;
_button = value;
}
}
protected override void OnInitialized(EventArgs e)
{
InitializeComponent();
base.OnInitialized(e);
this._button.Content = _btn.Content;
this._button.Background = _btn.Background;
this.Width = _btn.Width;
this.Height = _btn.Height;
}
}
It is going to work undoubtly.
回答5:
Another Option based on @Funk's answer is to make a content control instead of a button on the template, then bind the content control's content to your ButtonProperty in the code behind:
on the template:
<ContentControl Content={Binding myButton} Width="200" Height="100"/>
in the template code behind:
public static readonly DependencyProperty myButtonProperty =
DependencyProperty.Register("Button", typeof(Button), typeof(Template),
new UIPropertyMetadata(new PropertyChangedCallback(ButtonChangedCallback)));
and then on the Main Window:
<Window.Resources>
<Button x:Key="UserButton"
Background="Yellow"
Content="Actual Button"
/>
</Window.Resources>
<Grid>
<templateCode:Template myButton="{StaticResource UserButton}"/>
</Grid>
The nice thing about this is that Visual Studio is smart enough to show this code at design time, as well as having less code overall.
You can set things constant things (like location, font, and coloring) for your button either on the content control or in a default style, and then modify just the parts you need for you button.
回答6:
One option is to simply start writing C# on the xaml page using < ![CDATA[ *** ]]>
In the Main Window.xaml you change to:
<templateCode:Template x:Name="test">
<x:Code><![CDATA[
Void OnStartup()
{
test.MyButton.Content="Actual Button";
test.MyButton.Background = new SolidColorBrush(Color.FromArgb(255,255,255,0));
}
]]>
</x:Code>
Then right after Initialize Object() you call OnStartup().
Although this does let you edit specific properties in the xaml, this is about the same as just writing the code in the code behind, where others expect it to be.
来源：https://stackoverflow.com/questions/39886903/how-do-i-access-buttons-inside-a-usercontrol-from-xaml