CODEWITHSUNDEEP
c#wpf
Julien Leray
Julien Leray

Reputation: 1687

Get hard coded param from WPF UserControl to code behind

I 'm trying to do something really simple: I have a UserControl, where I want to pass a simple string parameter.

WPF MessagePage.xaml

<Page
    x:Class="MuchroomPhone.MessagePage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:MuchroomPhone"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

//...
<PivotItem Header="Nouveaux">
                <local:MessageUC MessType="new"/>
        </PivotItem>
        <PivotItem Header="Lus" >
            <local:MessageUC MessType="read"/>
        </PivotItem>
        <PivotItem Header="Envoyés" >
            <local:MessageUC MessType="send"/>
        </PivotItem>
        <PivotItem Header="Tous" >
            <local:MessageUC MessType="all"/>
        </PivotItem>
//...

I want to get the MessType from the code behind of the MessageUC.

eg. : I want to get the string "new" in the MessageUC.xaml.cs

I've tried that so far:

MessageUC.xaml

<UserControl
    x:Class="MuchroomPhone.MessageUC"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:MuchroomPhone"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300"
    d:DesignWidth="400">
//I don't think the content of the UC is important for my issue, but if you wanted to I can give it too.

MessageUC.xaml.cs

 public sealed partial class MessageUC : UserControl
    {
        public string _messType;

        public string MessType
        {
           get{ return _messType;}
           set{this._messType = value;}
        }
        public ObservableCollection<Message> listMessages { get; set; }

        public MessageUC()
        {
            this.InitializeComponent();
            Debug.WriteLine(MessType);
            this.fetchUserData();           
        }

But the MessType string is empty... Any ideas how to achieve that?

PS: I think there should be a way less verbose way for do that, so if you know a "simple" trick, would be great! Thanks

EDIT: So If I use a simple property, it's should work? Cause I still have null on MessType...

I've also tried with a Dependency Property, and MessType is an empty string.

EDIT 2: I think I understand what is wrong. Actually MessType doesn't exist on MessageUC.xaml. So the code behind can't find it. Perhaps isn it possible to just pass variable to my Page MessagePage.xaml directly to the User Control MessageUC?

Upvotes: 0

Views: 123

Answers (3)

Liero
Liero

Reputation: 27360

all you need is move fetchUserData to loaded event:

public sealed partial class MessageUC : UserControl
{
    public string MessType { get; set; }

    public MessageUC()
    {
        InitializeComponent();
        Debug.Writeline(MessType); //null
        Loaded += MessageUC_Loaded;
    }

    public void MessageUC_Loaded(object sender, EventArgs e)
    {
        Debug.Writeline(MessType); //new
        this.fetchUserData();
    }
}

DependencyProperty is not needed! Your original code doesn't work, because ctor in invoked before the property is set. DependecyProperty does not solve this, but enables databinding, styling, animating of the property.

Upvotes: 1

PiotrWolkowski
PiotrWolkowski

Reputation: 8792

This is a set of instructions that should work. However you didn't show the definition of your control so the code below may need some modifications and adjustments.

So start with registering a dependency property:

public static readonly DependencyProperty _messTypeProperty =
    DependencyProperty.Register("_messType", typeof(String),
    typeof(MessageUC), new FrameworkPropertyMetadata(string.Empty));

public String _messType
{
    get { return GetValue(_messTypeProperty).ToString(); }
    set { SetValue(_messTypeProperty, value); }
}

Add a name to your control in XAML:

<UserrControl x:Class="myNamespace.MessageUC"
    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"
    x:Name="MyUserControl">

In the XAML definition of your MessageUC control, in the code where you implement MessType bind it to the property in the code behind. Point to your control using the name you added to the control definition:

MessType="{Binding Path=_messType, ElementName=MyUserControl}"

Upvotes: 0

Rob Dunbar
Rob Dunbar

Reputation: 161

You only need a DependencyProperty if you want to data bind to it. In your case you can just use a normal property.

Upvotes: 0

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