Search and Replace

A WPF word processor needs to find text for its users and for its own code: users look for a word or replace a name throughout a contract, and your code fills in placeholders or checks a document for a term. The WPF TextControl covers both with built-in Find and Replace dialog boxes, sidebars and a Find method that returns the position of a match.

The examples use a window with a TextControl named textControl1, as in Create Your First WPF Application. The text positions that Find returns are explained on Selections and Caret Position.

Find and Replace for Users

With the WPF ribbon, the Editing group of the Home tab has buttons to find, replace and go to a place in the document, which open dialog boxes or connected sidebars.

In your own buttons and menus, Find without parameters opens the built-in Find dialog box, and Replace the Replace dialog box. The dialog boxes search the main text and, if the user chooses, text frames and headers and footers. The Replace dialog box also offers to match case, to match whole words only and to search upward:

The following window has three buttons above the editor. MainWindow.xaml:

<Window x:Class="SampleApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:WPF="clr-namespace:TXTextControl.WPF;assembly=TXTextControl.WPF"
        Title="MainWindow" Height="450" Width="800">
    <DockPanel>
        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal">
            <Button Content="Find..." Click="Find_Click" />
            <Button Content="Replace..." Click="Replace_Click" />
            <Button Content="Replace All" Click="ReplaceAll_Click" />
        </StackPanel>
        <WPF:TextControl x:Name="textControl1" Loaded="TextControl1_Loaded" />
    </DockPanel>
</Window>

The code-behind comes in the section Replace All Occurrences. The built-in keyboard assignment of the editor doesn't include Ctrl+F or Ctrl+H; Keyboard Shortcuts shows how to add them.

Find and Replace in a Sidebar

A Sidebar shows the find and replace functions as a panel beside the document instead of a dialog box. Set its ContentLayout to Find or Replace from SidebarContentLayout, and set its TextControl property to the name of the editor:

<DockPanel>
    <WPF:Sidebar x:Name="replaceSidebar" DockPanel.Dock="Right" HorizontalAlignment="Right" Width="250"
                ContentLayout="Replace" TextControl="textControl1" />
    <WPF:TextControl x:Name="textControl1" />
</DockPanel>

A sidebar aligned to the left or right edge arranges its content vertically, one aligned to the top or bottom horizontally. To have the ribbon buttons open your sidebars, set FindSidebar and ReplaceSidebar of the RibbonFormattingTab to the names of vertical sidebars, and FindHorizontalSidebar and ReplaceHorizontalSidebar to horizontal ones. Sidebar and Panels covers the setup.

Find Text in Code

Two overloads of Find search without a dialog box and return a zero-based text position:

The return value is the position of the first character of the match, or -1 if nothing is found. The search covers the text part with the input focus: the main text, or a header, footer or text frame the user is editing.

FindOptions values are combined with |:

Set NoMessageBox whenever your code searches on its own, so that no message box interrupts it.

Replace All Occurrences

MainWindow.xaml.cs for the window above writes a sentence into the editor when it is loaded. Replace All replaces every "order" with "purchase", and the other two buttons open the dialog boxes. Replace SampleApp with the namespace of your project:

using System.Windows;
using TXTextControl;

namespace SampleApp;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void TextControl1_Loaded(object sender, RoutedEventArgs e)
    {
        textControl1.Text = "Invoice for order 1234. Thank you for your order.";
    }

    // Open the built-in dialog boxes
    private void Find_Click(object sender, RoutedEventArgs e) => textControl1.Find();

    private void Replace_Click(object sender, RoutedEventArgs e) => textControl1.Replace();

    private void ReplaceAll_Click(object sender, RoutedEventArgs e)
    {
        int count = ReplaceAll("order", "purchase");
        MessageBox.Show(this, count + " replacements");
    }

    private int ReplaceAll(string searchText, string replacementText)
    {
        FindOptions options = FindOptions.MatchWholeWord | FindOptions.NoMessageBox;
        int count = 0;

        // All replacements are undone in one step
        textControl1.BeginUndoAction("Replace All");

        try
        {
            int position = textControl1.Find(searchText, 0, options);

            while (position != -1)
            {
                textControl1.Select(position, searchText.Length);
                textControl1.Selection.Text = replacementText;
                count++;

                // Continue behind the inserted text
                position = textControl1.Find(searchText, position + replacementText.Length, options);
            }
        }
        finally
        {
            textControl1.EndUndoAction();
        }

        return count;
    }
}

Click Replace All: a message box reports 2 replacements, and the text reads "Invoice for purchase 1234. Thank you for your purchase."

The code works as follows:

• MatchWholeWord keeps "order" from matching inside words such as "orders", and NoMessageBox keeps the search silent.
• Select selects each match, and Selection.Text replaces it.
• The next search starts behind the inserted text, so a replacement that contains the search text is not found again.
• BeginUndoAction and EndUndoAction turn all replacements into one step that Ctrl+Z undoes at once. See Undo and Redo.

Search Headers, Footers and Text Frames

To search all parts of a document regardless of the input focus, loop through TextParts. It contains the main text, the headers and footers and the text frames, each an IFormattedText object with its own Find and Selection.

The following method, added to MainWindow.xaml.cs, gives every occurrence of a text a yellow background:

private void HighlightEverywhere(string searchText)
{
    foreach (IFormattedText textPart in textControl1.TextParts)
    {
        int position = textPart.Find(searchText, 0, FindOptions.NoMessageBox);

        while (position != -1)
        {
            textPart.Selection = new Selection(position, searchText.Length) { TextBackColor = System.Drawing.Color.Yellow };
            position = textPart.Find(searchText, position + searchText.Length, FindOptions.NoMessageBox);
        }
    }
}

TextBackColor of the shared Selection class is a System.Drawing.Color, also in a WPF application, so the color is written with its full name.

Search With Regular Expressions

Find searches for literal text. For patterns such as dates or email addresses, apply a .NET regular expression to the text and select the matches by their positions, as the blog article Advanced Smart Search with Regular Expressions in .NET C# shows.

Next Steps

• Undo and Redo: group changes into one undo step.
• Keyboard Shortcuts: assign Ctrl+F and Ctrl+H.
• Built-in Dialog Boxes: the other dialog boxes of the editor.
• Fields, Hyperlinks, and Bookmarks: mark text that your code replaces later, instead of searching for it.