如何从代码隐藏构造函数访问 DependencyProperty 值?
我有一个名为 SmartForm 的 UserControl,它有一个名为 Status 的 DependencyProperty。
在我的 Window1.xaml 中,我有元素
。
我认为在 SmartForm 对象的构造函数中,Status 将等于“Ready”,但它等于 null。
为什么 SmartForm 的构造函数中 Status 属性的值为 NULL?
如果不在 UserControl 构造函数中,那么我什么时候可以访问该值?
Window1.xaml:
<Window x:Class="TestPropertyDefine23282.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TestPropertyDefine23282"
Title="Window1" Height="300" Width="300">
<Grid>
<local:SmartForm Status="Ready"/>
</Grid>
</Window>
SmartForm.xaml:
<UserControl x:Class="TestPropertyDefine23282.SmartForm"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Height="300" Width="300">
<Grid>
<TextBlock x:Name="TestingMessage"/>
</Grid>
</UserControl>
SmartForm.xaml.cs:
using System.Windows;
using System.Windows.Controls;
namespace TestPropertyDefine23282
{
public partial class SmartForm : UserControl
{
public SmartForm()
{
InitializeComponent();
TestingMessage.Text = Status; //WHY IS STATUS NOT YET SET HERE?
}
#region DependencyProperty: Status
public string Status
{
get
{
return (string)GetValue(StatusProperty);
}
set
{
SetValue(StatusProperty, value);
}
}
public static readonly DependencyProperty StatusProperty =
DependencyProperty.Register("Status", typeof(string), typeof(SmartForm),
new FrameworkPropertyMetadata());
#endregion
}
}
I have a UserControl called SmartForm which has a DependencyProperty called Status.
In my Window1.xaml, I have the element <local:SmartForm Status="Ready"/>
.
I would think then in the constructor of the SmartForm object, that Status would equal "Ready" but instead it equals null.
Why is then the value of the Status property NULL in the constructor of SmartForm?
If not in the UserControl constructor, when do I have access to the value, then?
Window1.xaml:
<Window x:Class="TestPropertyDefine23282.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TestPropertyDefine23282"
Title="Window1" Height="300" Width="300">
<Grid>
<local:SmartForm Status="Ready"/>
</Grid>
</Window>
SmartForm.xaml:
<UserControl x:Class="TestPropertyDefine23282.SmartForm"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Height="300" Width="300">
<Grid>
<TextBlock x:Name="TestingMessage"/>
</Grid>
</UserControl>
SmartForm.xaml.cs:
using System.Windows;
using System.Windows.Controls;
namespace TestPropertyDefine23282
{
public partial class SmartForm : UserControl
{
public SmartForm()
{
InitializeComponent();
TestingMessage.Text = Status; //WHY IS STATUS NOT YET SET HERE?
}
#region DependencyProperty: Status
public string Status
{
get
{
return (string)GetValue(StatusProperty);
}
set
{
SetValue(StatusProperty, value);
}
}
public static readonly DependencyProperty StatusProperty =
DependencyProperty.Register("Status", typeof(string), typeof(SmartForm),
new FrameworkPropertyMetadata());
#endregion
}
}
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评论(4)
翻译为:
当调用 setter 时,您将可以访问该值。
Translates to:
You will have access to that value when the setter is called.
您可以将该测试消息设置为:
或设置为:
You can set that testing message as:
Or as:
Szymon Rozga 很好地解释了这个问题。 您可以在设置参数之前、构造函数初始化之后检查参数。
一个好的解决方案是使用已加载的事件,如下所示:(
未经测试)
Szymon Rozga exlained the problem in a great way. You check the parameter before it is set but after the constructor is initialized.
A good solution is using the loaded event instead like so:
(Untested)
这是第三种,但为什么你需要这个二传手呢?
This is kind of tertiary, but why do you need this setter at all?