在自定义UserControl上添加额外控件

Question

I need to create custom UserControl so I can easily add some control so all control that implement CustomUserControl can affected.

This is what I do

public class CustomUserControl : UserControl
    {
        public CustomUserControl()
        {
            var stack = new StackPanel();
            stack.Children.Add(new TextBox() { Width = 100, Height = 100 });
            Content = stack; // need to add extra control to content
            //AddChild("test"); // this also fail
            //AddChild(stack); // this result in hard error
        }
    }

in the xaml

<control:CustomUserControl x:Class="Sample"
             xmlns:control="clr-namespace:Sample.Controls;assembly=Sample"
             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="300" d:DesignWidth="300">
    <Grid>
            <TextBox Width="100" Height="100"/>
    </Grid>
</control:CustomUserControl>

I want it to show 2 textbox, but it only show one, maybe because content overrided by parent.

Answer 1

Your constructor code is executing after XAML generation. Your content first setting to "Grid" in XAML, then "Content = stack" in .cs file. You need to set name to your grid in xaml and use it name in .cs file. But don't do it, please, use MVVM.

Answer 2

If you want a custom user control with two text boxes in it, just do that in the control's XAML: you don't need to do it in the constructor.

In other words, delete your constructor:

public class CustomUserControl : UserControl
{
}

and get rid of the Grid in the XAML:

<control:CustomUserControl x:Class="Sample" ... >
    <StackPanel>
        <TextBox Width="100" Height="100"/>
        <TextBox Width="100" Height="100"/>
    </StackPanel>
</control:CustomUserControl>

Answer 3

After digging UserControl and trial error I finally get what I want, just override on render in user control

protected override void OnRender(System.Windows.Media.DrawingContext drawingContext)
        {
            if (_group == null) //private field, hack so it only adding content once
            {
                var grid = new StackPanel() { Orientation = Orientation.Vertical };
                _group = new WarningBoxControl();

                var content = Content as StackPanel;
                if (content != null)
                {
                    _group.DataContext = content.DataContext;
                    content.Children.Insert(0, _group);
                }
            }

            base.OnRender(drawingContext);
        }

The only problem with this is Control that implement CustomUserControl must have stack panel at its root. regardless this was easaier to maintain whenever I want to put extra control or something

Answer 4

But if you want to add it from code you to give a name to the grid, then add childs from code. For example XAML:

<UserControl x:Class="WpfApplication1.UserControl1"
         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="300" d:DesignWidth="300">
<Grid x:Name="MyGrid">
    <Grid.RowDefinitions>
        <RowDefinition Height="29*"/>
        <RowDefinition Height="271*"/>
    </Grid.RowDefinitions>
    <TextBlock Text="TextBox1 Text" Grid.Row="0"/>
</Grid>

And .cs file will be:

public UserControl1()
    {
        InitializeComponent();
        var textBlock2 = new TextBlock();
        textBlock2.Text = "TextBox2 Text";
        MyGrid.Children.Add(textBlock2);
        Grid.SetRow(textBlock2,1);
    }
}