wpf 设计时 XAML 的默认值
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Default value at design time XAML
提问by Sherlock
I have a binded TextBlock, XAML:
我有一个绑定的TextBlockXAML：
<TextBlock Text="{Binding MyText}"/>
I know the FallbackValuecan be used if the Binding isn't available, but this happens at run time ? Is there any way to show a default value at design time ? It would make things easier if I could see a value when designing my windows instead of an empty TextBlock.
我知道FallbackValue如果 Binding 不可用，则可以使用它，但这会在运行时发生吗？有没有办法在设计时显示默认值？如果我在设计窗口时可以看到一个值而不是一个空的TextBlock.
Thanks
谢谢
回答by Scroog1
If you would prefer a less verbose version of Ian Bamforth's answer, you can just do
如果您更喜欢Ian Bamforth 的答案的不那么冗长的版本，您可以这样做
<TextBlock Text="{Binding MyText, FallbackValue=None}"/>
回答by IBam
回答by user3618238
If you have this data bound and are using the MVVM architecture then setting a DEFAULT value for the model item it is bound to will display the value at design time
如果您绑定了此数据并且正在使用 MVVM 架构，则为其绑定的模型项设置 DEFAULT 值将在设计时显示该值
I am just using:
我只是在使用：
Model.cs:
模型.cs：
private int frame = 999999;
public int Frame
{
get { return frame; }
set
{
frame = value;
NotifyPropertyChanged(m => m.Frame);
}
}
and in my XAML:
在我的 XAML 中：
<TextBlock Text="{Binding Path=Frame}" />
and the default value of "999999" is being displayed in the designer
并且在设计器中显示“999999”的默认值
回答by Thomas Levesque
Using FallbackValueis wrong, because it also affects the runtime behavior (the fallback value is used if the binding fails to obtain a value from the source).
使用FallbackValue是错误的，因为它还会影响运行时行为（如果绑定无法从源获取值，则使用回退值）。
I came up with a custom markup extension that mimics Binding(ideally I would have preferred to inherit from Binding, but the ProvideValuemethod is not virtual...):
我想出了一个模仿的自定义标记扩展Binding（理想情况下我宁愿继承自Binding，但该ProvideValue方法不是虚拟的......）：
using System;
using System.ComponentModel;
using System.Windows;
using System.Windows.Data;
using System.Windows.Markup;
namespace MyNamespace
{
public class BindingEx : MarkupExtension
{
private readonly Binding _binding;
public BindingEx()
{
_binding = new Binding();
}
public BindingEx(string path)
{
_binding = new Binding(path);
}
public PropertyPath Path
{
get => _binding.Path;
set => _binding.Path = value;
}
public BindingMode Mode
{
get => _binding.Mode;
set => _binding.Mode = value;
}
public RelativeSource RelativeSource
{
get => _binding.RelativeSource;
set => _binding.RelativeSource = value;
}
public string ElementName
{
get => _binding.ElementName;
set => _binding.ElementName = value;
}
public IValueConverter Converter
{
get => _binding.Converter;
set => _binding.Converter = value;
}
public object DesignValue { get; set; }
public override object ProvideValue(IServiceProvider serviceProvider)
{
var target = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget));
if (target.TargetObject is DependencyObject d && DesignerProperties.GetIsInDesignMode(d))
return DesignValue;
return _binding.ProvideValue(serviceProvider);
}
}
}
You can use it just like Binding, with the addition of the DesignValueproperty:
您可以像 一样使用它Binding，并添加以下DesignValue属性：
<TextBlock Text="{my:BindingEx Name, DesignValue=John Doe}" />
Note that BindingExdoesn't have all the properties from Binding, but you can easily add them if necessary.
请注意，BindingEx没有来自 的所有属性Binding，但您可以在必要时轻松添加它们。
