How to Dynamically Adjust the Width of Blazor DropDownList?

The Blazor DropDownList component is a versatile control that enables users to select an option from a list. While the width of the DropDownList is static by default, there are instances where a dynamic adjustment of the DropDownList width based on the length of the selected text is desirable. This can be accomplished using the Width property in combination with Bitmap.

Overview

The approach involves using the ValueChange event of the DropDownList to detect when the selected value changes. When this event is triggered, the text of the selected item is retrieved and its width when rendered in a specific font is calculated. This width calculation is done using a Bitmap object, which is a part of the System.Drawing namespace in .NET.


A Bitmap is a two-dimensional grid of pixels that can be manipulated individually or collectively to create graphics. In this case, a Bitmap is used to create a Graphics object, which provides methods for drawing text, shapes, and images onto the Bitmap. The MeasureString method of the Graphics object is then used to calculate the width of the selected text when rendered in a specific font.


Once the width of the selected text is obtained, the width of the DropDown List is adjusted accordingly. If no item is selected, the width of the DropDownList is set to a default value.

Setting up the DropDownList

First, the DropDownList is set up with a dynamic width and a ValueChange event handler.

<div id="ControlRegion" style="margin:150px auto;width:100%">
    <SfDropDownList ID="ddl" TItem="GameFields" Width="@DDLwidth" TValue="string" ShowClearButton="true" Placeholder="Select a game" DataSource="@Games">
        <DropDownListEvents TItem="GameFields" TValue="string" ValueChange="@ValueChangeHandler"></DropDownListEvents>
        <DropDownListFieldSettings Text="Text" Value="ID"></DropDownListFieldSettings>
    </SfDropDownList>
</div>

Defining the Data Model

A simple data model for the items in the DropDownList is defined.

public class GameFields
{
    public string ID { get; set; }
    public string Text { get; set; }
}

Populating the DropDownList

Next, the DropDownList is populated with some sample data.

public List<GameFields> Games = new List<GameFields>() {
    new GameFields(){ ID= "Game1", Text= "American Football" },
    new GameFields(){ ID= "Game2", Text= "Badminton" },
    new GameFields(){ ID= "Game4", Text= "Cricket" },
    new GameFields(){ ID= "Game6", Text= "Golf" }
};

Handling Value Changes

When the selected value changes, the width of the selected text is calculated and the width of the DropDownList is adjusted.

private void ValueChangeHandler(ChangeEventArgs<string, GameFields> args)
{
    var Selected_Text = (args.ItemData != null) ? args.ItemData.Text : "";
    DDLwidth = (Selected_Text != "") ? (MeasureTextWidth(Selected_Text, new Font("Arial", 14, FontStyle.Regular)) + 30).ToString() + "px" : "50%";
    StateHasChanged();
}

Measuring Text Width

A method that measures the width of a given text string when rendered in a specified font is defined.

public static float MeasureTextWidth(string text, Font font)
{
    using (Bitmap bitmap = new Bitmap(1, 1))
    {
        using (Graphics g = Graphics.FromImage(bitmap))
        {
            SizeF size = g.MeasureString(text, font);
            return size.Width;
        }
    }
}

This approach effectively adjusts the width of the DropDownList based on the length of the selected text, providing a practical solution to a common requirement in numerous web applications.

Sample:

For a live demonstration of the dynamic Adjust the Width of a DropDownList Component in Blazor, you can refer to the following sample:

Conclusion
I hope you enjoyed learning how to dynamically adjust the width of Blazor DropDownList.
You can refer to our Blazor DropDownList feature tour page to know about its other groundbreaking feature representations and documentation, and how to quickly get started for configuration specifications. You can also explore our Blazor DropDownList example to understand how to create and manipulate data.

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