动态网格填充绑定问题ActualWidth的 [英] Binding issue ActualWidth on dynamic filled Grid

问题描述

考虑下面，简单code：

Consider the following, simple code:

XAML：

<Grid Height="60" Name="grid">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="162*" />
        <ColumnDefinition x:Name="coltest" Width="316*" />
        <ColumnDefinition Width="239*" />
    </Grid.ColumnDefinitions>
</Grid>
<Label MouseDoubleClick="TextBox_MouseDoubleClick" 
    Content="{Binding ElementName=coltest, Path=ActualWidth}" Grid.Row="1"/>

的 MouseDoubleClick 事件：

The MouseDoubleClick event:

private void TextBox_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
    grid.RowDefinitions.Add(new RowDefinition());
    for (int i = 0; i < grid.ColumnDefinitions.Count; i++)
    {
        Random r = new Random();
        Label l = new Label { Content = r.Next(10, 1000000000).ToString() };
        grid.Children.Add(l);
        Grid.SetRow(l, grid.RowDefinitions.Count - 1);
        Grid.SetColumn(l, i);
    }
}

---

我的标签包含通过绑定第二列的 ActualWidth的属性。在Visual Studio中我看到包含我的标签值316，所以结合的作品。

---

My label contains the ActualWidth property of the second column via a binding. In Visual Studio I see my label containing the value 316, so the binding works.

双击标签触发其事件并增加了一个额外的行到网格，所有随机长度。

Double clicking the label triggers its event and adds an extra row to the grid, all with a random length.

我希望看到我的标签的新价值，但（该计算运行时间）0不会改变！

I expect to see a new value at my label, but (the at runtime calculated) 0 does not change!

我是什么在这里失踪？

推荐答案

主要的问题是， ActualWidth的的 Col​​umnDefinition 不是一个依赖项属性，也没有实施 INotifyPropertyChanged的所以绑定没有办法知道的 ActualWidth的 COLTEST已经改变了。

The main problem is that ActualWidth of a ColumnDefinition isn't a Dependency Property, nor does it implement INotifyPropertyChanged so the Binding has no way of knowing that the ActualWidth of coltest has changed.

您需要显式地更新绑定

EDIT2：在这种情况下，你也许可以在时，SizeChanged 绑定 $ C>事件的电网因为列有 * 宽度。这不会与自动工作宽度100％，但由于宽度将改变基于 Col​​umnDefinition <元素/ p>

In this case, you might be able to update the Binding in the SizeChanged event for the Grid since the Columns have * width. This won't work 100% with Auto width though since the width will change based on the elements in the ColumnDefinition

<Grid Name="grid"
      SizeChanged="grid_SizeChanged">
    <!--...-->
</Grid>

的事件处理程序的

void grid_SizeChanged(object sender, SizeChangedEventArgs e)
{
    BindingExpression be = label.GetBindingExpression(Label.ContentProperty);
    be.UpdateTarget();
}

编辑：提出了一些小的变化到XAML。这将更新您双击第一个标签上的绑定每次

Made some small changes to the Xaml. This will update the Binding everytime you doubleclick the first Label

<Grid Name="grid">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="162*" />
        <ColumnDefinition x:Name="coltest" Width="316*" />
        <ColumnDefinition Width="239*" />
        <ColumnDefinition Width="239*" />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
    </Grid.RowDefinitions>
    <Label MouseDoubleClick="TextBox_MouseDoubleClick"
           Name="label"
           Content="{Binding ElementName=coltest, Path=ActualWidth}" Grid.Row="0"/>
</Grid>

的事件处理程序的

private void TextBox_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
    grid.RowDefinitions.Add(new RowDefinition());
    for (int i = 0; i < grid.ColumnDefinitions.Count; i++)
    {
        Random r = new Random();
        Label l = new Label { Content = r.Next(10, 1000000000).ToString() };
        grid.Children.Add(l);
        Grid.SetRow(l, grid.RowDefinitions.Count - 1);
        Grid.SetColumn(l, i);
    }
    BindingExpression be = label.GetBindingExpression(Label.ContentProperty);
    be.UpdateTarget();
}

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