MaxLength on editable combobox stops working when mahapps is referenced

[Chrullbo]

We have set maxlength on a editable combobox by dependency property and when mahapps is referenced the maxlenght is ignored. We use the string "PART_EditableTextBox" to find the textbox in the visualtree of the combobox that is revealed when editing is enabled

[punker76]

@Chrullbo i figured it out, that the loaded stuff should be respect

so this works for me™ (and maybe it can be added to MahApps directly)

        public static readonly DependencyProperty MaxLengthProperty = DependencyProperty.RegisterAttached("MaxLength", typeof(int), typeof(ComboBoxHelper), new FrameworkPropertyMetadata(0, MaxLengthPropertyChangedCallback), new ValidateValueCallback(MaxLengthValidateValue));

        private static bool MaxLengthValidateValue(object value)
        {
            return ((int)value) >= 0;
        }

        private static void MaxLengthPropertyChangedCallback(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
        {
            var comboBox = dependencyObject as ComboBox;
            if (comboBox != null)
            {
                comboBox.Loaded -= comboBox_Loaded;
                if (e.NewValue != e.OldValue && e.NewValue is int)
                {
                    if (comboBox.IsLoaded)
                    {
                        SetMaxLengthToTextBox(comboBox, (int)e.NewValue);
                    }
                    else
                    {
                        comboBox.Loaded += comboBox_Loaded;
                    }
                }
            }
        }

        static void comboBox_Loaded(object sender, RoutedEventArgs e)
        {
            SetMaxLengthToTextBox((ComboBox)sender, GetMaxLength((ComboBox)sender));
        }

        private static void SetMaxLengthToTextBox(ComboBox comboBox, int maxLength)
        {
            var textBox = comboBox.FindChild<TextBox>("PART_EditableTextBox");
            if (textBox != null)
            {
                textBox.MaxLength = maxLength;
            }
        }

        public static void SetMaxLength(DependencyObject obj, int value)
        {
            obj.SetValue(MaxLengthProperty, value);
        }

        public static int GetMaxLength(DependencyObject obj)
        {
            return (int)obj.GetValue(MaxLengthProperty);
        }

usage

<TextBox Text="{Binding ElementName=ComboBoxTest, Path=(Controls:ComboBoxHelper.MaxLength), Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
<ComboBox Width="200"
            x:Name="ComboBoxTest"
            Controls:TextBoxHelper.ClearTextButton="True"
            Margin="0, 10, 0, 0"
            SelectedIndex="0"
            Controls:ComboBoxHelper.MaxLength="3"
            IsEditable="True">
    <ComboBoxItem Content="Item 1" />
    <ComboBoxItem Content="Item 2" />
    <ComboBoxItem Content="Very long Item 3 for MahApps.Metro" />
    <ComboBoxItem Content="Item 4" />
</ComboBox>

[Chrullbo]

thx, that worked like a charm

[thoemmi]

LGTM, though I would add comboBox.Loaded -= comboBox_Loaded in comboBox_Loaded.

[punker76]

@thoemmi you're right. for MahApps i can use the attached property directly
with binding, so the loaded stuff is not needed.
Am 01.06.2015 19:29 schrieb "Thomas Freudenberg" notifications@github.com:

LGTM, though I would add comboBox.Loaded -= comboBox_Loaded in
comboBox_Loaded.

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#1948 (comment)
.

[thoemmi]

+1 on integrating it in MA.M 😄

[punker76]

@thoemmi -> #1949