Menambahkan tempat penampung pada Kotak Teks

Contoh berikut menunjukkan cara menampilkan teks tempat penampung dalam TextBox saat TextBox kosong. Ketika TextBox memiliki teks, teks tempat penampung disembunyikan. Teks tempat penampung membantu pengguna memahami jenis input yang diharapkan oleh TextBox.

Di artikel ini, Anda akan mempelajari cara:

Buat properti terlampirkan untuk menyediakan teks placeholder.
Buat sebuah adorner untuk menampilkan teks placeholder.
Tambahkan properti terlampir ke TextBox kontrol.

Membuat properti terlampir

Dengan properti terlampir, Anda dapat menambahkan nilai ke kontrol. Anda sering menggunakan fitur ini di WPF, seperti saat Anda mengatur Grid.Row atau Panel.ZIndex properti pada kontrol. Untuk informasi lebih lanjut, lihat Gambaran Umum Properti Terlampir. Contoh ini menggunakan properti terlampir untuk menambahkan teks placeholder ke TextBox.

Tambahkan kelas baru ke proyek Anda bernama TextBoxHelper dan buka.

Tambahkan namespace berikut:

using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Media;

Imports System.Linq
Imports System.Security.Cryptography
Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Documents
Imports System.Windows.Media

Buat properti dependensi baru bernama Placeholder.

Properti dependensi ini menggunakan callback perubahan properti delegasi.

public static string GetPlaceholder(DependencyObject obj) =>
    (string)obj.GetValue(PlaceholderProperty);

public static void SetPlaceholder(DependencyObject obj, string value) =>
    obj.SetValue(PlaceholderProperty, value);

public static readonly DependencyProperty PlaceholderProperty =
    DependencyProperty.RegisterAttached(
        "Placeholder",
        typeof(string),
        typeof(TextBoxHelper),
        new FrameworkPropertyMetadata(
            defaultValue: null,
            propertyChangedCallback: OnPlaceholderChanged)
        );

Public Shared Function GetPlaceholder(obj As DependencyObject) As String
    Return obj.GetValue(PlaceholderProperty)
End Function

Public Shared Sub SetPlaceholder(obj As DependencyObject, value As String)
    obj.SetValue(PlaceholderProperty, value)
End Sub

Public Shared ReadOnly PlaceholderProperty As DependencyProperty =
    DependencyProperty.RegisterAttached(
        "Placeholder",
        GetType(String),
        GetType(TextBoxHelper),
        New FrameworkPropertyMetadata(
            defaultValue:=Nothing,
            propertyChangedCallback:=AddressOf OnPlaceholderChanged)
        )

OnPlaceholderChanged Buat metode untuk mengintegrasikan properti terlampir dengan TextBox.

private static void OnPlaceholderChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    if (d is TextBox textBoxControl)
    {
        if (!textBoxControl.IsLoaded)
        {
            // Ensure that the events are not added multiple times
            textBoxControl.Loaded -= TextBoxControl_Loaded;
            textBoxControl.Loaded += TextBoxControl_Loaded;
        }

        textBoxControl.TextChanged -= TextBoxControl_TextChanged;
        textBoxControl.TextChanged += TextBoxControl_TextChanged;

        // If the adorner exists, invalidate it to draw the current text
        if (GetOrCreateAdorner(textBoxControl, out PlaceholderAdorner adorner))
            adorner.InvalidateVisual();
    }
}

Private Shared Sub OnPlaceholderChanged(d As DependencyObject, e As DependencyPropertyChangedEventArgs)
    Dim textBoxControl = TryCast(d, TextBox)

    If textBoxControl IsNot Nothing Then

        If Not textBoxControl.IsLoaded Then

            'Ensure that the events are not added multiple times
            RemoveHandler textBoxControl.Loaded, AddressOf TextBoxControl_Loaded
            AddHandler textBoxControl.Loaded, AddressOf TextBoxControl_Loaded

        End If

        RemoveHandler textBoxControl.TextChanged, AddressOf TextBoxControl_TextChanged
        AddHandler textBoxControl.TextChanged, AddressOf TextBoxControl_TextChanged

        'If the adorner exists, invalidate it to draw the current text
        Dim adorner As PlaceholderAdorner = Nothing
        If GetOrCreateAdorner(textBoxControl, adorner) Then
            adorner.InvalidateVisual()
        End If

    End If

End Sub

Ada dua cara metode ini dipanggil ketika nilai properti terlampir berubah:

Ketika properti terlampir pertama kali ditambahkan ke TextBox, metode ini dipanggil. Tindakan tersebut memberikan kesempatan bagi properti terlampir untuk diintegrasikan dengan peristiwa kontrol.
Setiap kali properti ini diubah, adorner dapat diatur ulang untuk memperbarui teks penempatan visual.

Metode GetOrCreateAdorner ini dibuat di bagian berikutnya.

Buat penanganan aktivitas untuk TextBox.

private static void TextBoxControl_Loaded(object sender, RoutedEventArgs e)
{
    if (sender is TextBox textBoxControl)
    {
        textBoxControl.Loaded -= TextBoxControl_Loaded;
        GetOrCreateAdorner(textBoxControl, out _);
    }
}

private static void TextBoxControl_TextChanged(object sender, TextChangedEventArgs e)
{
    if (sender is TextBox textBoxControl
        && GetOrCreateAdorner(textBoxControl, out PlaceholderAdorner adorner))
    {
        // Control has text. Hide the adorner.
        if (textBoxControl.Text.Length > 0)
            adorner.Visibility = Visibility.Hidden;

        // Control has no text. Show the adorner.
        else
            adorner.Visibility = Visibility.Visible;
    }
}

Private Shared Sub TextBoxControl_Loaded(sender As Object, e As RoutedEventArgs)
    Dim textBoxControl As TextBox = TryCast(sender, TextBox)

    If textBoxControl IsNot Nothing Then
        RemoveHandler textBoxControl.Loaded, AddressOf TextBoxControl_Loaded
        GetOrCreateAdorner(textBoxControl, Nothing)
    End If
End Sub

Private Shared Sub TextBoxControl_TextChanged(sender As Object, e As TextChangedEventArgs)
    Dim textBoxControl As TextBox = TryCast(sender, TextBox)
    Dim adorner As PlaceholderAdorner = Nothing

    If textBoxControl IsNot Nothing AndAlso GetOrCreateAdorner(textBoxControl, adorner) Then

        If textBoxControl.Text.Length > 0 Then
            'Control has text. Hide the adorner.
            adorner.Visibility = Visibility.Hidden
        Else
            'Control has no text. Show the adorner.
            adorner.Visibility = Visibility.Visible
        End If

    End If
End Sub

Peristiwa Loaded ditangani sehingga adorner dapat dibuat setelah templat kontrol diterapkan. Handler menghapus dirinya sendiri setelah acara dinaikkan dan adorner dibuat.

Peristiwa TextChanged ditangani untuk memastikan bahwa adorner disembunyikan atau ditampilkan tergantung apakah Text memiliki nilai tertentu.

Membuat penghias

Adorner adalah visual yang terikat ke kontrol dan dirender dalam AdornerLayer. Untuk informasi selengkapnya, lihat Gambaran Umum Adorners.

TextBoxHelper Buka kelas .

Tambahkan kode berikut untuk membuat GetOrCreateAdorner metode .

private static bool GetOrCreateAdorner(TextBox textBoxControl, out PlaceholderAdorner adorner)
{
    // Get the adorner layer
    AdornerLayer layer = AdornerLayer.GetAdornerLayer(textBoxControl);

    // If null, it doesn't exist or the control's template isn't loaded
    if (layer == null)
    {
        adorner = null;
        return false;
    }

    // Layer exists, try to find the adorner
    adorner = layer.GetAdorners(textBoxControl)?.OfType<PlaceholderAdorner>().FirstOrDefault();

    // Adorner never added to control, so add it
    if (adorner == null)
    {
        adorner = new PlaceholderAdorner(textBoxControl);
        layer.Add(adorner);
    }

    return true;
}

Private Shared Function GetOrCreateAdorner(textBoxControl As TextBox, ByRef adorner As PlaceholderAdorner) As Boolean

    'Get the adorner layer
    Dim layer As AdornerLayer = AdornerLayer.GetAdornerLayer(textBoxControl)

    'If nothing, it doesn't exist or the control's template isn't loaded
    If layer Is Nothing Then
        adorner = Nothing
        Return False
    End If

    'Layer exists, try to find the adorner
    adorner = layer.GetAdorners(textBoxControl)?.OfType(Of PlaceholderAdorner)().FirstOrDefault()

    'Adorner never added to control, so add it
    If adorner Is Nothing Then
        adorner = New PlaceholderAdorner(textBoxControl)
        layer.Add(adorner)
    End If

    Return True

End Function

Metode ini menyediakan cara yang aman untuk menambahkan atau mengambil Adorner. Adorner memerlukan keamanan ekstra karena ditambahkan ke kontrol AdornerLayer, yang mungkin tidak ada. Saat properti terlampir XAML diterapkan ke kontrol, templat kontrol belum diterapkan untuk membuat pohon visual, sehingga lapisan adorner tidak ada. Lapisan adorner harus diambil setelah kontrol dimuat. Lapisan adorner mungkin juga hilang jika templat yang menghilangkan lapisan adorner diterapkan pada kontrol.

Tambahkan kelas anak bernama PlaceholderAdorner ke kelas TextBoxHelper.

public class PlaceholderAdorner : Adorner
{
    public PlaceholderAdorner(TextBox textBox) : base(textBox) { }

    protected override void OnRender(DrawingContext drawingContext)
    {
        TextBox textBoxControl = (TextBox)AdornedElement;

        string placeholderValue = TextBoxHelper.GetPlaceholder(textBoxControl);

        if (string.IsNullOrEmpty(placeholderValue))
            return;

        // Create the formatted text object
        FormattedText text = new FormattedText(
                                    placeholderValue,
                                    System.Globalization.CultureInfo.CurrentCulture,
                                    textBoxControl.FlowDirection,
                                    new Typeface(textBoxControl.FontFamily,
                                                 textBoxControl.FontStyle,
                                                 textBoxControl.FontWeight,
                                                 textBoxControl.FontStretch),
                                    textBoxControl.FontSize,
                                    SystemColors.InactiveCaptionBrush,
                                    VisualTreeHelper.GetDpi(textBoxControl).PixelsPerDip);

        text.MaxTextWidth = System.Math.Max(textBoxControl.ActualWidth - textBoxControl.Padding.Left - textBoxControl.Padding.Right, 10);
        text.MaxTextHeight = System.Math.Max(textBoxControl.ActualHeight, 10);

        // Render based on padding of the control, to try and match where the textbox places text
        Point renderingOffset = new Point(textBoxControl.Padding.Left, textBoxControl.Padding.Top);

        // Template contains the content part; adjust sizes to try and align the text
        if (textBoxControl.Template.FindName("PART_ContentHost", textBoxControl) is FrameworkElement part)
        {
            Point partPosition = part.TransformToAncestor(textBoxControl).Transform(new Point(0, 0));
            renderingOffset.X += partPosition.X;
            renderingOffset.Y += partPosition.Y;

            text.MaxTextWidth = System.Math.Max(part.ActualWidth - renderingOffset.X, 10);
            text.MaxTextHeight = System.Math.Max(part.ActualHeight, 10);
        }

        // Draw the text
        drawingContext.DrawText(text, renderingOffset);
    }
}

Public Class PlaceholderAdorner
    Inherits Adorner

    Public Sub New(adornedElement As UIElement)
        MyBase.New(adornedElement)
    End Sub

    Protected Overrides Sub OnRender(drawingContext As DrawingContext)
        Dim textBoxControl As TextBox = DirectCast(AdornedElement, TextBox)

        Dim placeholderValue As String = TextBoxHelper.GetPlaceholder(textBoxControl)

        If String.IsNullOrEmpty(placeholderValue) Then
            Return
        End If

        'Create the formatted text object
        Dim text As New FormattedText(
            placeholderValue,
            System.Globalization.CultureInfo.CurrentCulture,
            textBoxControl.FlowDirection,
            New Typeface(textBoxControl.FontFamily,
                         textBoxControl.FontStyle,
                         textBoxControl.FontWeight,
                         textBoxControl.FontStretch),
            textBoxControl.FontSize,
            SystemColors.InactiveCaptionBrush,
            VisualTreeHelper.GetDpi(textBoxControl).PixelsPerDip)

        text.MaxTextWidth = Math.Max(textBoxControl.ActualWidth - textBoxControl.Padding.Left - textBoxControl.Padding.Right, 10)
        text.MaxTextHeight = Math.Max(textBoxControl.ActualHeight, 10)

        'Render based on padding of the control, to try and match where the textbox places text
        Dim renderingOffset As New Point(textBoxControl.Padding.Left, textBoxControl.Padding.Top)

        'Template contains the content part; adjust sizes to try and align the text
        Dim part As FrameworkElement = TryCast(textBoxControl.Template.FindName("PART_ContentHost", textBoxControl), FrameworkElement)

        If part IsNot Nothing Then
            Dim partPosition As Point = part.TransformToAncestor(textBoxControl).Transform(New Point(0, 0))
            renderingOffset.X += partPosition.X
            renderingOffset.Y += partPosition.Y

            text.MaxTextWidth = Math.Max(part.ActualWidth - renderingOffset.X, 10)
            text.MaxTextHeight = Math.Max(part.ActualHeight, 10)
        End If

        ' Draw the text
        drawingContext.DrawText(text, renderingOffset)
    End Sub

End Class

Seorang pujaan mewarisi dari Adorner kelas. Adorner khusus ini mengganti metode OnRender(DrawingContext) untuk menggambar teks tempat penampung. Mari kita uraikan kode:

Pertama, periksa apakah teks tempat penampung ada dengan memanggil TextBoxHelper.GetPlaceholder(textBoxControl).
Buat objek FormattedText. Objek ini berisi semua informasi tentang teks apa yang digambar pada visual.
FormattedText.MaxTextWidth Properti dan FormattedText.MaxTextHeight diatur ke wilayah kontrol. Mereka juga menetapkan nilai minimum 10 untuk memastikan FormattedText objek valid.
renderingOffset menyimpan posisi teks yang digambar.
Gunakan PART_ContentHost jika templat kontrol menyatakannya. Bagian ini mewakili tempat teks digambar pada templat kontrol. Jika bagian tersebut ditemukan, ubah renderingOffset untuk memperhitungkan posisinya.
Gambarkan teks dengan memanggil DrawText(FormattedText, Point) dan mengoper objek FormattedText serta posisi teks.

Terapkan properti terlampir

Setelah properti terlampir didefinisikan, ruang nama tersebut perlu diimpor ke dalam XAML, lalu direferensikan pada sebuah kontrol TextBox. Kode berikut memetakan namespace .NET DotnetDocsSample ke namespace XML l.

<Window x:Class="DotnetDocsSample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:l="clr-namespace:DotnetDocsSample"
        Title="Recipe Tracker" Width="400" SizeToContent="Height">
    <StackPanel Margin="10">
        <TextBlock FontSize="20" TextWrapping="Wrap">Welcome to Recipe Tracker! To get started, create a new account.</TextBlock>
        
        <Label Padding="0,5">Name</Label>
        <TextBox l:TextBoxHelper.Placeholder="Ex. Jeffry Goh" />
        
        <Label Padding="0,5">Email</Label>
        <TextBox l:TextBoxHelper.Placeholder="jeffry@contoso.com" />
        
        <Label Padding="0,5">Password</Label>
        <PasswordBox />
        
        <Button HorizontalAlignment="Right" Width="100" Margin="0,10,0,5">Submit</Button>
    </StackPanel>
</Window>

Properti terlampir ditambahkan ke TextBox menggunakan sintaks xmlNamespace:Class.Property.

Contoh lengkap

Kode berikut adalah kelas lengkap TextBoxHelper .

public static class TextBoxHelper
{
    public static string GetPlaceholder(DependencyObject obj) =>
        (string)obj.GetValue(PlaceholderProperty);

    public static void SetPlaceholder(DependencyObject obj, string value) =>
        obj.SetValue(PlaceholderProperty, value);

    public static readonly DependencyProperty PlaceholderProperty =
        DependencyProperty.RegisterAttached(
            "Placeholder",
            typeof(string),
            typeof(TextBoxHelper),
            new FrameworkPropertyMetadata(
                defaultValue: null,
                propertyChangedCallback: OnPlaceholderChanged)
            );

    private static void OnPlaceholderChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is TextBox textBoxControl)
        {
            if (!textBoxControl.IsLoaded)
            {
                // Ensure that the events are not added multiple times
                textBoxControl.Loaded -= TextBoxControl_Loaded;
                textBoxControl.Loaded += TextBoxControl_Loaded;
            }

            textBoxControl.TextChanged -= TextBoxControl_TextChanged;
            textBoxControl.TextChanged += TextBoxControl_TextChanged;

            // If the adorner exists, invalidate it to draw the current text
            if (GetOrCreateAdorner(textBoxControl, out PlaceholderAdorner adorner))
                adorner.InvalidateVisual();
        }
    }

    private static void TextBoxControl_Loaded(object sender, RoutedEventArgs e)
    {
        if (sender is TextBox textBoxControl)
        {
            textBoxControl.Loaded -= TextBoxControl_Loaded;
            GetOrCreateAdorner(textBoxControl, out _);
        }
    }

    private static void TextBoxControl_TextChanged(object sender, TextChangedEventArgs e)
    {
        if (sender is TextBox textBoxControl
            && GetOrCreateAdorner(textBoxControl, out PlaceholderAdorner adorner))
        {
            // Control has text. Hide the adorner.
            if (textBoxControl.Text.Length > 0)
                adorner.Visibility = Visibility.Hidden;

            // Control has no text. Show the adorner.
            else
                adorner.Visibility = Visibility.Visible;
        }
    }

    private static bool GetOrCreateAdorner(TextBox textBoxControl, out PlaceholderAdorner adorner)
    {
        // Get the adorner layer
        AdornerLayer layer = AdornerLayer.GetAdornerLayer(textBoxControl);

        // If null, it doesn't exist or the control's template isn't loaded
        if (layer == null)
        {
            adorner = null;
            return false;
        }

        // Layer exists, try to find the adorner
        adorner = layer.GetAdorners(textBoxControl)?.OfType<PlaceholderAdorner>().FirstOrDefault();

        // Adorner never added to control, so add it
        if (adorner == null)
        {
            adorner = new PlaceholderAdorner(textBoxControl);
            layer.Add(adorner);
        }

        return true;
    }

    public class PlaceholderAdorner : Adorner
    {
        public PlaceholderAdorner(TextBox textBox) : base(textBox) { }

        protected override void OnRender(DrawingContext drawingContext)
        {
            TextBox textBoxControl = (TextBox)AdornedElement;

            string placeholderValue = TextBoxHelper.GetPlaceholder(textBoxControl);

            if (string.IsNullOrEmpty(placeholderValue))
                return;

            // Create the formatted text object
            FormattedText text = new FormattedText(
                                        placeholderValue,
                                        System.Globalization.CultureInfo.CurrentCulture,
                                        textBoxControl.FlowDirection,
                                        new Typeface(textBoxControl.FontFamily,
                                                     textBoxControl.FontStyle,
                                                     textBoxControl.FontWeight,
                                                     textBoxControl.FontStretch),
                                        textBoxControl.FontSize,
                                        SystemColors.InactiveCaptionBrush,
                                        VisualTreeHelper.GetDpi(textBoxControl).PixelsPerDip);

            text.MaxTextWidth = System.Math.Max(textBoxControl.ActualWidth - textBoxControl.Padding.Left - textBoxControl.Padding.Right, 10);
            text.MaxTextHeight = System.Math.Max(textBoxControl.ActualHeight, 10);

            // Render based on padding of the control, to try and match where the textbox places text
            Point renderingOffset = new Point(textBoxControl.Padding.Left, textBoxControl.Padding.Top);

            // Template contains the content part; adjust sizes to try and align the text
            if (textBoxControl.Template.FindName("PART_ContentHost", textBoxControl) is FrameworkElement part)
            {
                Point partPosition = part.TransformToAncestor(textBoxControl).Transform(new Point(0, 0));
                renderingOffset.X += partPosition.X;
                renderingOffset.Y += partPosition.Y;

                text.MaxTextWidth = System.Math.Max(part.ActualWidth - renderingOffset.X, 10);
                text.MaxTextHeight = System.Math.Max(part.ActualHeight, 10);
            }

            // Draw the text
            drawingContext.DrawText(text, renderingOffset);
        }
    }
}

Public Class TextBoxHelper

    Public Shared Function GetPlaceholder(obj As DependencyObject) As String
        Return obj.GetValue(PlaceholderProperty)
    End Function

    Public Shared Sub SetPlaceholder(obj As DependencyObject, value As String)
        obj.SetValue(PlaceholderProperty, value)
    End Sub

    Public Shared ReadOnly PlaceholderProperty As DependencyProperty =
        DependencyProperty.RegisterAttached(
            "Placeholder",
            GetType(String),
            GetType(TextBoxHelper),
            New FrameworkPropertyMetadata(
                defaultValue:=Nothing,
                propertyChangedCallback:=AddressOf OnPlaceholderChanged)
            )

    Private Shared Sub OnPlaceholderChanged(d As DependencyObject, e As DependencyPropertyChangedEventArgs)
        Dim textBoxControl = TryCast(d, TextBox)

        If textBoxControl IsNot Nothing Then

            If Not textBoxControl.IsLoaded Then

                'Ensure that the events are not added multiple times
                RemoveHandler textBoxControl.Loaded, AddressOf TextBoxControl_Loaded
                AddHandler textBoxControl.Loaded, AddressOf TextBoxControl_Loaded

            End If

            RemoveHandler textBoxControl.TextChanged, AddressOf TextBoxControl_TextChanged
            AddHandler textBoxControl.TextChanged, AddressOf TextBoxControl_TextChanged

            'If the adorner exists, invalidate it to draw the current text
            Dim adorner As PlaceholderAdorner = Nothing
            If GetOrCreateAdorner(textBoxControl, adorner) Then
                adorner.InvalidateVisual()
            End If

        End If

    End Sub

    Private Shared Sub TextBoxControl_Loaded(sender As Object, e As RoutedEventArgs)
        Dim textBoxControl As TextBox = TryCast(sender, TextBox)

        If textBoxControl IsNot Nothing Then
            RemoveHandler textBoxControl.Loaded, AddressOf TextBoxControl_Loaded
            GetOrCreateAdorner(textBoxControl, Nothing)
        End If
    End Sub

    Private Shared Sub TextBoxControl_TextChanged(sender As Object, e As TextChangedEventArgs)
        Dim textBoxControl As TextBox = TryCast(sender, TextBox)
        Dim adorner As PlaceholderAdorner = Nothing

        If textBoxControl IsNot Nothing AndAlso GetOrCreateAdorner(textBoxControl, adorner) Then

            If textBoxControl.Text.Length > 0 Then
                'Control has text. Hide the adorner.
                adorner.Visibility = Visibility.Hidden
            Else
                'Control has no text. Show the adorner.
                adorner.Visibility = Visibility.Visible
            End If

        End If
    End Sub


    Private Shared Function GetOrCreateAdorner(textBoxControl As TextBox, ByRef adorner As PlaceholderAdorner) As Boolean

        'Get the adorner layer
        Dim layer As AdornerLayer = AdornerLayer.GetAdornerLayer(textBoxControl)

        'If nothing, it doesn't exist or the control's template isn't loaded
        If layer Is Nothing Then
            adorner = Nothing
            Return False
        End If

        'Layer exists, try to find the adorner
        adorner = layer.GetAdorners(textBoxControl)?.OfType(Of PlaceholderAdorner)().FirstOrDefault()

        'Adorner never added to control, so add it
        If adorner Is Nothing Then
            adorner = New PlaceholderAdorner(textBoxControl)
            layer.Add(adorner)
        End If

        Return True

    End Function

    Public Class PlaceholderAdorner
        Inherits Adorner

        Public Sub New(adornedElement As UIElement)
            MyBase.New(adornedElement)
        End Sub

        Protected Overrides Sub OnRender(drawingContext As DrawingContext)
            Dim textBoxControl As TextBox = DirectCast(AdornedElement, TextBox)

            Dim placeholderValue As String = TextBoxHelper.GetPlaceholder(textBoxControl)

            If String.IsNullOrEmpty(placeholderValue) Then
                Return
            End If

            'Create the formatted text object
            Dim text As New FormattedText(
                placeholderValue,
                System.Globalization.CultureInfo.CurrentCulture,
                textBoxControl.FlowDirection,
                New Typeface(textBoxControl.FontFamily,
                             textBoxControl.FontStyle,
                             textBoxControl.FontWeight,
                             textBoxControl.FontStretch),
                textBoxControl.FontSize,
                SystemColors.InactiveCaptionBrush,
                VisualTreeHelper.GetDpi(textBoxControl).PixelsPerDip)

            text.MaxTextWidth = Math.Max(textBoxControl.ActualWidth - textBoxControl.Padding.Left - textBoxControl.Padding.Right, 10)
            text.MaxTextHeight = Math.Max(textBoxControl.ActualHeight, 10)

            'Render based on padding of the control, to try and match where the textbox places text
            Dim renderingOffset As New Point(textBoxControl.Padding.Left, textBoxControl.Padding.Top)

            'Template contains the content part; adjust sizes to try and align the text
            Dim part As FrameworkElement = TryCast(textBoxControl.Template.FindName("PART_ContentHost", textBoxControl), FrameworkElement)

            If part IsNot Nothing Then
                Dim partPosition As Point = part.TransformToAncestor(textBoxControl).Transform(New Point(0, 0))
                renderingOffset.X += partPosition.X
                renderingOffset.Y += partPosition.Y

                text.MaxTextWidth = Math.Max(part.ActualWidth - renderingOffset.X, 10)
                text.MaxTextHeight = Math.Max(part.ActualHeight, 10)
            End If

            ' Draw the text
            drawingContext.DrawText(text, renderingOffset)
        End Sub

    End Class
End Class

Lihat juga

Ringkasan Kotak Teks
Gambaran Umum Adorners
Gambaran Umum Properti Terlampir

Saran dan Komentar

Apakah halaman ini membantu?

Last updated on 2025-05-07