CODEWITHSUNDEEP
c#wpf
Sebastian Ax
Sebastian Ax

Reputation: 1350

How to get the next line with TextPointer.GetLineStartPosition() in a RichTextBox

I'm trying to get the lines of the RichTextBox.

Here they show how to do it:
Using GetLineStartPosition to get the end of a line in WPF RichTextBox

But for whatever reason I always get null as the return of GetLineStartPosition(1).

XAML

    <Grid>
        <StackPanel>
            <Button Height="40" Click="Button_Click"></Button>

            <RichTextBox x:Name="rtbEditor">
                <FlowDocument>
                    <Paragraph>Hello, world!
                        a
                        <LineBreak/>
                        b
                        <LineBreak/>
                        c
                        <LineBreak/>
                        d
                    </Paragraph>
                </FlowDocument>
            </RichTextBox>
        </StackPanel>
    </Grid>

Code

        public MainWindow()
        {
            InitializeComponent();

            rtbEditor.AppendText("testtext" + "\r");
            rtbEditor.AppendText("testtext" + "\r");
            rtbEditor.AppendText("testtext" + "\r");
            rtbEditor.AppendText("testtext" + "\r\n");
            rtbEditor.AppendText("testtext" + "\r\n");
            rtbEditor.AppendText("testtext" + "\r\n");
            rtbEditor.AppendText("testtext" + "\n");
            rtbEditor.AppendText("testtext" + "\n");
            rtbEditor.AppendText("testtext" + "\n");
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            TextPointer contentStart = rtbEditor.Document.ContentStart;
            var nextStart = contentStart.GetLineStartPosition(1);
        }

nextStart is null. What am I doing wrong here?

Upvotes: 1

Views: 420

Answers (1)

Keith Stein
Keith Stein

Reputation: 6724

This took a bit of research into how FlowDocuments and TextPointers worked. I'd suggest reading the TextPointer Remarks Section because it really helped me understand this.

My theory is that the GetLineStartPosition method won't work if the current TextPointer doesn't have a Paragraph to reference. Document.ContentStart gives you a TextPointer that's just before the first Paragraph in the FlowDocument. You can call GetNextInsertionPosition(LogicalDirection.Forward) to return a TextPointer to the next valid insertion point- in this case the first valid insertion point- in the document. From there you are inside the first Paragraph and GetLineStartPosition starts to work.

TextPointer contentStart = rtbEditor.Document.ContentStart.GetNextInsertionPosition(LogicalDirection.Forward);
var nextStart = contentStart.GetLineStartPosition(1);

Upvotes: 1

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