CODEWITHSUNDEEP
c#xamlmvvmuwp
Bolke
Bolke

Reputation: 107

Textbox binding won't update on RaisePropertychanged

Using Mvvm library, UWP, C#.

Problem: View won't update content of a textbox if value is changed in the viewmodel and the textbox has focus on that moment. It is possible to update a viewmodel property of a textbox that hasn't got the focus.

To clear confusion: Textbox -> Has focus -> Something is typed -> Is passed to bound property -> Property set, changes value and calls RaisePropertyChange. -> Textbox does not update.

If the property that is bound to a different TextBox is changed in the ViewModel, and RaisePropertyChanged is called with that property as target, that TextBox does get updated.

The difference seems to be that the Textbox that has focus doesn't update on RaisePropertyChanged. It does do this in wpf.

Code below is an example, not the actual application. It does show the problem, and acts just like the actual application. Hyphen is added to change the input. If RaisePropertyChanged did work, the hyphen would show up in the editbox, it doesn't.

My page:

<Page x:Class="BindingTest.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:BindingTest.VML"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
DataContext="{Binding MainViewModel, Source={StaticResource Locator}}" >

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}" Margin="0,144,0,109">
    <TextBox x:Name="textBox1" 
             Text="{Binding Item1, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" 
             HorizontalAlignment="Left" 
             Margin="10,137,0,0" 
             TextWrapping="Wrap" 
             VerticalAlignment="Top" 
             Width="340"/>

    <TextBox x:Name="textBox2" 
             Text="{Binding Item2, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" 
             HorizontalAlignment="Left" 
             Margin="10,174,0,0" 
             TextWrapping="Wrap"
             VerticalAlignment="Top" 
             Width="340"/>
</Grid>

My ViewModel:

using GalaSoft.MvvmLight;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Input;

namespace BindingTest
{
    public class MainViewModel:ViewModelBase
    {        
        string _item1 = "";
        string _item2 = "";

        public string Item1 {
            get
            {
                return _item1;
            }
            set
            {
                _item1 = value + "-";
                RaisePropertyChanged("Item1");                               
            }
        }

        public string Item2
        {
            get {
                return _item2;
            }
            set
            {
                _item2 = value + "-";
                RaisePropertyChanged("Item2");
            }
        }
    }
}

If text is put into either one of the textboxes, the set of the properties is called, value is changed, value isn't updated in the textbox.

If I would call the propertychanged of textbox2 in the setter of textbox1, it will update:

        public string Item1 {
            get
            {
                return _item1;
            }
            set
            {
                _item2 = value + "-";
                RaisePropertyChanged("Item2");                               
            }
        }

It is as if the textbox that has the focus won't update it's content as long as it has the focus.

Upvotes: 2

Views: 1310

Answers (2)

Akli
Akli

Reputation: 1549

Here is trick I use:

Instead of calling RaisePropertyChanged() call the following method :

    public async void ForceRaisePropertyChanged(string propName)
    {
        await Task.Delay(1);
        RaisePropertyChanged(propName);
    }

It works like a charm.

Upvotes: 0

Alpine13
Alpine13

Reputation: 152

Try removing

updateSourceTrigger=PropertyChanged

from your textbox binding

RaisePropertyChanged on the viewmodel should be enough

Upvotes: 0

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