WPF 设计时错误对象引用未设置为对象的实例
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WPF design time error Object reference not set to an instance of an object
提问by Micha? Jankowski
Ok I am getting sick of this problem.
好吧，我厌倦了这个问题。
I am trying to make UserControl where I can populate its content from XAML. Previously I have created ObservableCollection DependencyProperty. It was working at runtime but at design time there was an error:
我正在尝试使 UserControl 可以从 XAML 填充其内容。之前我已经创建了 ObservableCollection DependencyProperty。它在运行时工作，但在设计时出现错误：
Object reference not set to an instance of an object.
你调用的对象是空的。
Now I did simpler version:
现在我做了更简单的版本：
public partial class UC : UserControl
{
public UC()
{
Labels = new ObservableCollection<Label>();
InitializeComponent();
Labels.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(Labels_CollectionChanged);
}
void Labels_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
foreach (Label uc in e.NewItems)
Container.Children.Add(uc);
}
private ObservableCollection<Label> _lables = new ObservableCollection<Label>();
public ObservableCollection<Label> Labels
{
get { return _lables; }
set { _lables = value; }
}
}
This is how I like to use my UserControll
这就是我喜欢使用我的 UserControll 的方式
<Window x:Class="WpfApplication1.MainWindow"
xmlns:gsh="clr-namespace:WpfApplication1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid Margin="0,0,0,30">
<gsh:UC x:Name="uC1">
<gsh:UC.Labels>
<Label Content="qwerty1" />
<Label Content="qwerty2" />
</gsh:UC.Labels>
</gsh:UC>
</Grid>
However it still gives me the error at design time:
但是它在设计时仍然给我错误：
Object reference not set to an instance of an object.
你调用的对象是空的。
So if anyone can help me please.
所以如果有人可以帮助我，请。
How can I make UserControl that I can use like native controls which I can populate with collection of elements? I am trying to find the answer second day already.
如何使 UserControl 可以像我可以使用元素集合填充的本机控件一样使用？我已经在第二天试图找到答案。
回答by Richard Friend
I usually check to see if i am in design time before wiring up events etc..
我通常在连接事件等之前检查我是否处于设计时间。
It could be that your Container is null in design mode.
可能是您的 Container 在设计模式下为空。
public class Utils
{
public static bool IsInDesignerMode
{
get
{
return ((bool)(DesignerProperties.IsInDesignModeProperty
.GetMetadata(typeof(DependencyObject)).DefaultValue));
}
}
}
Maybe in your constructor you should do this..
也许在你的构造函数中你应该这样做..
public UC()
{
InitializeComponent();
if (!Utils.IsInDesignerMode)
{
Labels = new ObservableCollection<Label>();
Labels.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(Labels_CollectionChanged);
}
}
On another note though i think you would be better using an ItemsControl
另一方面，尽管我认为您最好使用ItemsControl
