在编写新文本之前清除RichTextBox

Question

I'm using Visual Studio, WPF, C#, XAML.

I have a RichTextBox that C# writes text to on button press.

Each time the button is pressed it appends the new text to the RichTextBox, leaving the old text.

I need it to clear the old text before writing the new, so it doesn't stack up.

XAML

<RichTextBox Name="richTextBox1" IsUndoEnabled="False" />

C#

Clear

richTextBox1.Document.Blocks.Clear();

---

public static System.Windows.Media.Brush White = (SolidColorBrush)(new BrushConverter().ConvertFrom("#FFFFFF"));
public static Paragraph paragraph = new Paragraph();

// Button
private void btnWrite_Click(object sender, RoutedEventArgs e) {

    //Clear() put here, does nothing


    // New Document
    richTextBox1.Document = new FlowDocument(paragraph);


    //Clear() put here works but wont write new text, stays blank


    //begin writing
    richTextBox1.BeginChange();

        //Clear() put here works but wont write new text, stays blank

        //write text
        paragraph.Inlines.Add(new Run("Hello, World.") { Foreground = White });

    //end writing
    richTextBox1.EndChange();


    richTextBox1.UpdateLayout(); //does nothing
}

Answer 1

There are three ways to clear the text of the RichTextBox:

1. Use the clear method:

    richTextBox1.Document.Blocks.Clear(); 

   As I mentioned, this way doesn't work for you

2. Select all of your RichTextBox and set the Text to "":

    richTextBox1.SelectAll(); richTextBox1.Selection.Text = ""; 

   Do this, before you start to change.

3. Use TextRange, to get the text and clear it with "":

    TextRange txt = new TextRange(richTextBox1.Document.ContentStart, richTextBox1.Document.ContentEnd); txt.Text=""; 

My answer is a conclusion from this question: how to clear text content in RichTextBox

---

Update : You can try the following:

1. Create an object from FlowDocument:

    FlowDocument ObjFdoc = new FlowDocument(); 

2. Create a paragraph:

    Paragraph paragraph = new Paragraph(); paragraph.Inlines.Add(new Run("Hello, World.") { Foreground = White }); 

3. Add the paragraph to the FlowDocument:

    ObjFdoc.Blocks.Add(ObjPara1); 

4. Set the RichtTextBox.Document:

    richTextBox1.Document=ObjFdoc; 

Every time you call your method, it will be generate a new flowdocument and gc deletes the old flowdocuments for you.

Answer 2

I need 50 reputation to comment...

Is there a particular reason for you to assign a new FlowDocument to the RichTextBox every time the button is pressed?

You're clearing the documents content in the Clear() method and than attach a new FlowDocument object with the entire paragraph to the RichTextBox , thus appending the new text to the same paragraph.

Try removing the richTextBox1.Document = new FlowDocument(paragraph); line.

Answer 3

Because the text was added in a paragraph (Block) contained in your FlowDocument( richtextBox1.Document ) it has to be cleared using this code:

 paragraph.Inlines.Clear(); 

Explanation: The issue here is that you are clearing all blocks from your FlowDocument, including your single paragraph so next time you want to append text in that paragraph it won't work, of course, the text is added to the paragraph referenced by paragraph but it is not part of the document any more.

Here are some unit Tests

 [Apartment(ApartmentState.STA)]
    public class Tests
    {
        public static System.Windows.Media.Brush White = (SolidColorBrush)(new BrushConverter().ConvertFrom("#FFFFFF"));
        protected Paragraph paragraph;
        protected RichTextBox richTextBox1;

        [SetUp]
        public void Setup()
        {
            richTextBox1 = new RichTextBox();
            paragraph = new Paragraph();
            richTextBox1.Document = new FlowDocument(paragraph);
        }

        /// <summary>
        /// This reproduce the issue
        /// </summary>
        [Test]
        public void Adding_Text_After_Blocks_Clear_Should_Not_Work_The_issue()
        {
            paragraph.AddText("Hello, World!");

            string content1 = richTextBox1.GetText();

            Assert.AreEqual("Hello, World!", content1);

            richTextBox1.Document.Blocks.Clear();

            string content2 = richTextBox1.GetText();

            Assert.AreEqual("", content2);

            paragraph.AddText("Howdy!");

            string content3 = richTextBox1.GetText();

            //are not equal
            Assert.AreNotEqual("Howdy!", content3);
        }

        [Test]
        public void Adding_TextAfter_Paragraph_Clear_Should_Work_Solution()
        {
            paragraph.AddText("Hello, World!");

            string content1 = richTextBox1.GetText();

            Assert.AreEqual("Hello, World!", content1);

            paragraph.Inlines.Clear();

            string content2 = richTextBox1.GetText();

            Assert.AreEqual("", content2);

            paragraph.AddText("Howdy!");

            string content3 = richTextBox1.GetText();

            Assert.AreEqual("Howdy!", content3);
        }

        /// <summary>
        /// Keep in mind tha if the  RichTextBox is not readonly, deleting text with CTRL-A + DELETE 
        /// Causes the same issues.
        /// </summary>
        [Test]
        public void Clearing_Blocks_Should_Remove_All_Paragraphs_The_Cause_of_issue()
        {
            paragraph.AddText("Hello, World!");

            string content1 = richTextBox1.GetText();

            Assert.AreEqual("Hello, World!", content1);

            var blocksBefore = richTextBox1.Document.Blocks.ToArray();

            Assert.IsTrue(ReferenceEquals(paragraph, blocksBefore[0]));

            richTextBox1.Document.Blocks.Clear();

            var blocksAfter = richTextBox1.Document.Blocks.ToArray();

            Assert.AreEqual(0, blocksAfter.Length);
        }


        [Test]
        public void Added_New_Text_after_Blocks_Clear_Should_Work()
        {
            paragraph.AddText("Hello, World!");

            string content1 = richTextBox1.GetText();

            Assert.AreEqual("Hello, World!", content1);

            richTextBox1.Document.Blocks.Clear();

            string content2 = richTextBox1.GetText();

            Assert.AreEqual("", content2);

            var p = new Paragraph();

            p.AddText("Howdy!");

            //Add this to the blocks collection!!!!
            richTextBox1.Document.Blocks.Add(p);

            string content3 = richTextBox1.GetText();

            Assert.AreEqual("Howdy!", content3);
        }
    }

    public static class RTBExtentions
    {
        public static string GetText(this RichTextBox rtb)
        {
            return new TextRange(rtb.Document.ContentStart, rtb.Document.ContentEnd).Text.TrimEnd();
        }
        public static void AddText(this Paragraph paragraph, string textToAdd, Brush foregroundColor = default(Brush))
        {
            paragraph.Inlines.Add(new Run(textToAdd) { Foreground = foregroundColor });
        }

        public static Block[] ToArray(this BlockCollection blocks)
        {
            List<Block> elements = new List<Block>();

            foreach (var item in blocks)  {  elements.Add(item);  }

            return elements.ToArray();
        }
    }