双向绑定仅适用于一项，而不适用于另一项

Question

I am currently building an uwp where users can add custom xaml-elements to the GUI and set certain properties. There are also general properties of the page that can be set. To do this there is a properties panel on the designpage.In this properties panel I want to either display the changeable properties from the xaml-element that is selected or (if the user selects one specific element) it should display the general properties. I want to use two-way databinding so that the values are dynamically displayed in the property panel, but also so that changes made in the propertypanel are passed to the source.

I had no problems implementing this two-way binding for displaying the details of the selected xaml-element, but for the general properties the binding appears to go only one-way. When a general property is changed in code, it is passed to the target object, but when data is changed in the GUI it doesn't pass the data to the source.

So I have searched the web and tried modifying my code by adding dependency properties, changing private<-->public, implementing INotifyPropertyChanged in various ways, etc. Unfortunately none of it seems to be working.

Below I will provide the both the working and non-functional c# code/xaml. If anybody can spot the problem I'd be most grateful.

General xaml for the target control in design page

<StackPanel x:Name="PropsPanel" Grid.Column="1" Grid.Row="1" Grid.RowSpan="2" Orientation="Vertical" Background="GhostWhite" BorderThickness="1" BorderBrush="GhostWhite" Margin="4">
         <TextBlock Text="Properties" Margin="4,4,0,40" Foreground="Black" FontWeight="Bold"/>
         <ContentControl Name="PropertiesPanel" Foreground="Black">
         </ContentControl>
</StackPanel>

Datatemplate xaml with working two-way binding for properties xaml-element

<DataTemplate x:Key="TimerElementTemplate">
    <Grid HorizontalAlignment="Stretch">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <TextBlock Grid.Row="0" Grid.Column="0" Margin="2" Text="Timer" FontWeight="SemiBold"/>
        <TextBlock Grid.Row="1" Grid.Column="0" Margin="2" Text="Column "/>
        <TextBlock Grid.Row="1" Grid.Column="1" Margin="2" Text="{Binding Path=ShowColumn, Mode=OneWay}" />
        <TextBlock Grid.Row="2" Grid.Column="0" Margin="2" Text="Row " />
        <TextBlock Grid.Row="2" Grid.Column="1" Margin="2" Text="{Binding Path=ShowRow, Mode=OneWay}"/>
        <TextBlock Grid.Row="3" Grid.Column="0" Margin="2" Text="Name "/>
        <TextBox Grid.Row="3" Grid.Column="1" BorderThickness="1" Margin="2" Text="{Binding Path=ElementName, Mode=TwoWay}" />
        <TextBlock Grid.Row="4" Grid.Column="0" Margin="2" Text="Label " />
        <TextBox Grid.Row="4" Grid.Column="1" Margin="2" BorderThickness="1" Text="{Binding Path=Label, Mode=TwoWay}" />
    </Grid>
</DataTemplate>

Working code for setting the datacontext

private void GOnPointerReleased(object sender, PointerRoutedEventArgs pointerRoutedEventArgs)
    {
        if (_selectedGuiElement != null)
        {
            _selectedGuiElement.BorderThickness = new Thickness(0);
        }
        PropertiesPanel.DataContext = sender;
        PropertiesPanel.ContentTemplate = Resources[sender.GetType().Name + "Template"] as DataTemplate;
        var element = sender as GuiElement;
        element.BorderBrush = new SolidColorBrush(Colors.Crimson);
        element.BorderThickness = new Thickness(2.0);
        _selectedGuiElement = element;

    }

The elements with the displayable properties are GUIelements that inherit from the Grid Xaml-control. The properties I display are marked with the GUIElementProperty-attribute. The code for the GUI-element is below:

public class GuiElement : Grid
{
    protected string _elementType;

    public GuiElement(bool design)
    {
        DesignState = design;
        SetElementType();
        AddContent();
        if(DesignState)
        AllowDrop = true;
    }

    //overridable method to set Type and Type related properties
    public virtual void SetElementType()
    {
        _elementType = "";
        GuiBackground = new SolidColorBrush(Colors.DarkGray);
    }
    //overridable method to set lay-out content for each type
    public virtual void AddContent()
    {
        Background = GuiBackground;
        BorderThickness = new Thickness(1);
        BorderBrush = new SolidColorBrush(Colors.GhostWhite);
        SetColumnSpan(this, ColumnSpan);
        SetRowSpan(this, RowSpan);
    }


    // shortcuts for Grid.Column and Grid.Row properties and other general properties
    [GuiElementProperty("lbl", "Column", 2)]
    public int Column
    {
        get { return GetColumn(this); }
        set { SetColumn(this, value); }
    }

    public string ShowColumn
    {
        get { return Column.ToString(); }
    }

    [GuiElementProperty("lbl", "Row", 1)]
    public int Row
    {
        get { return GetRow(this); }
        set { SetRow(this, value); }
    }

    public string ShowRow
    {
        get { return Row.ToString(); }
    }

    public int ColumnSpan { get; set; } = 1;

    public int RowSpan { get; set; } = 1;

    public bool DesignState { get; set; }

    public SolidColorBrush GuiBackground { get; set; }

    public int Id { get; set; }

    [GuiElementProperty("lbl", "Type", 0)]
    public string ElementType { get { return _elementType; } }
}

}

So far the working code...now the problematic part

Datatemplate xaml for displaying the general properties with dysfunctional two-way binding

<DataTemplate x:Key="StartElementTemplate">
    <Grid HorizontalAlignment="Stretch">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <TextBlock Grid.Row="0" Grid.Column="0" Margin="2" Text="Session" FontWeight="SemiBold"/>
        <!--<Button Foreground="GhostWhite" Grid.Row="0" Grid.Column="1" Content="X" Click="ButtonDeleteFromProperties_OnClick"></Button>-->
        <TextBlock Grid.Row="1" Grid.Column="0" Margin="2" Text="Name "/>
        <TextBlock Grid.Row="1" Grid.Column="1" Margin="2" Text="{Binding Path=DesignName, Mode=OneWay}"/>
        <TextBlock Grid.Row="2" Grid.Column="0" Margin="2" Text="Time Limit (true/false) "/>
        <TextBox Grid.Row="2" Grid.Column="1" Margin="2" BorderThickness="1" Text="{Binding Path=LimitedTime, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
        <TextBlock Grid.Row="3" Grid.Column="0" Margin="2" Text="Max. duration (hh:mm:ss) "/>
        <TextBox Grid.Row="3" Grid.Column="1" BorderThickness="1" Margin="2" Text="{Binding Path=Timelimit, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
    </Grid>
</DataTemplate>

the code for the class with the general properties

 public class SessionProps : INotifyPropertyChanged   
{   private string _designname;
   private bool _limitedtime;
   private TimeSpan _timelimit;

   [GuiElementProperty("txtbx", "Design name", 0)]
    public string DesignName
    {
        get { return _designname; }
        set
        {
            _designname = value;
            NotifyPropertyChanged();
        }
    }

    [GuiElementProperty("bool", "Time limit", 1)]
   public bool LimitedTime
    {
        get { return _limitedtime; }
        set
        {
            _limitedtime = value;
            NotifyPropertyChanged();
        }
    }

    [GuiElementProperty("txtbx", "Max. Duration (hh:mm:ss)", 2)]
   public TimeSpan Timelimit
    {
       get { return _timelimit; }
       set
       {
           _timelimit = value;
            NotifyPropertyChanged();
        } 
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

Creating an instance of the general properties class

 public sealed partial class DesignPage : Page
{
    private SessionProps _props = new SessionProps() {DesignName = "", LimitedTime = false, Timelimit = TimeSpan.Zero};

code binding control to this source

 private void SOnPointerReleased(object sender, PointerRoutedEventArgs e)
    {
        if (_selectedGuiElement != null)
        {
            _selectedGuiElement.BorderThickness = new Thickness(0);
        }
        PropsPanel.DataContext = _props;
        PropertiesPanel.ContentTemplate = Resources[sender.GetType().Name + "Template"] as DataTemplate;
        var element = sender as GuiElement;
        element.BorderBrush = new SolidColorBrush(Colors.Crimson);
        element.BorderThickness = new Thickness(2.0);
        _selectedGuiElement = element;
    }

I'm hoping there is just something small I'm overlooking here, but any help will be appreciated! I hope I have provided sufficient information, but if there is anything that's still unclear, please ask.

Answer 1

The reason is that the LimitedTime is bool type, Timelimit is TimeSpan type and the text in TextBox is string type. When you edit the TextBox , it will get an Error: Converter failed to convert value of type 'Windows.Foundation.String' to type 'Boolean';

You can create a class that allows you to convert the format of your data between the source and the target by inheriting from IValueConverter .

You should always implement Convert with a functional implementation, but it's fairly common to implement ConvertBack so that it reports a not-implemented exception. You only need a ConvertBack method in your converter if you are using the converter for two-way bindings, or using XAML for serialization.

For more info, see INotifyPropertyChanged .

For example:

public class BoolFormatter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        return value.ToString();
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        if (value.ToString() == "true" || value.ToString() == "True")
        {
            return true;
        }
        else if (value.ToString() == "false" || value.ToString() == "False")
        {
            return false;
        }
        else
        {
            return "";
        }
    }
}

Create TimeSpanFormatter class:

public class TimeSpanFormatter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        if (value != null)
        {
            return value.ToString();
        }
        else
        {
            return null;
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        TimeSpan span;

        if (TimeSpan.TryParse(value.ToString(), out span))
        {
            return span;
        }
        else
        {
            return "";
        }
    }
}

In XAML:

<Page.Resources>
    <local:BoolFormatter x:Key="BoolConverter" />
    <local:TimeSpanFormatter x:Key="TimeSpanConverter" />
    <DataTemplate>
        <Grid HorizontalAlignment="Stretch">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto" />
                <ColumnDefinition Width="*" />
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto" />
                <RowDefinition Height="Auto" />
                <RowDefinition Height="Auto" />
                <RowDefinition Height="Auto" />
                <RowDefinition Height="Auto" />
            </Grid.RowDefinitions>
            <TextBlock Grid.Row="0" Grid.Column="0" Margin="2" Text="Session" FontWeight="SemiBold" />
            <!--<Button Foreground="GhostWhite" Grid.Row="0" Grid.Column="1" Content="X" Click="ButtonDeleteFromProperties_OnClick"></Button>-->
            <TextBlock Grid.Row="1" Grid.Column="0" Margin="2" Text="Name " />
            <TextBlock Grid.Row="1" Grid.Column="1" Margin="2" Text="{Binding Path=DesignName, Mode=TwoWay}" />
            <TextBlock Grid.Row="2" Grid.Column="0" Margin="2" Text="Time Limit (true/false) " />
            <TextBox Grid.Row="2" Grid.Column="1" Margin="2" BorderThickness="1" Text="{Binding Path=LimitedTime, Mode=TwoWay,Converter={StaticResource BoolConverter}}" />
            <TextBlock Grid.Row="3" Grid.Column="0" Margin="2" Text="Max. duration (hh:mm:ss) " />
            <TextBox Grid.Row="3" Grid.Column="1" BorderThickness="1" Margin="2" Text="{Binding Path=Timelimit, Mode=TwoWay,Converter={StaticResource TimeSpanConverter}}" />
        </Grid>
    </DataTemplate>
</Page.Resources>