如何为发送到移动设备的垂直居中消息创建WYSIWYG TextBox控件编辑器？

Question

I have a WPF TextBox that holds seven lines of text and has word wrapping enbabled.

<TextBox TextWrapping="Wrap" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" MaxLines="7"/>

As you can see in the XAML above the text is centered vertically and horizontally. When I type a short phrase that fits on a single line, the text appears on the 4th line of the control as expected since the VerticalContentAlignment is "Center".

The text that is entered by the user is meant to be sent to a mobile device that has a display that holds seven lines of text and uses the "\\n" to wrap to the next line. The intent is that the display of text on the mobile device looks the same as what is entered into the TextBox control. At least as far as number of lines of text, centering, and where line breaks occur.

So when the the user finishes entering the text into the TextBox control and clicks the "Send Message" button, some post-processing must be done on the entered text before sending it to the mobile device.

The text entered into TextBox control needs to have newline (\\n) characters added wherever the text wraps to a new line in the TextBox control. For example, in cases where the control is showing multiple lines of text, I copy the TextBox's text and add a newline between the lines wehre the TextBox control wrapped the lines of text that were entered by the user.

So when the user clicks a "Send Message" button this is the code that does the post processing:

  public static String AddNewLineCharsToMessage(TextBox textBox)
  {
     String message = String.Empty;

     if (textBox == null) return message;

     // First strip all the carriage returns and newline characters
     // so we don't have duplicate newline characters in the message.
     // Then add back in just the newline characters which is what the 
     // mobile device uses to wrap lines.

     // Just assign the text if we have a single line message
     if (textBox.LineCount < 2)
        return textBox.Text;

     var textLines = new List<string>(5);
     int lineCount = Math.Min(textBox.LineCount, textBox.MaxLines);
     for (Int32 index = 0; index < lineCount; index++)
     {
        if (textBox.GetLineText(index).Length > 0)
        {
           textLines.Add(textBox.GetLineText(index));
           textLines[index] = textLines[index].Replace("\r", "");
           textLines[index] = textLines[index].Replace("\n", "");
        }
        else
           textLines.Add("\n");
     }

     message = String.Empty;
     for (Int32 index = 0; index < lineCount; index++)
        message += textLines[index] + (index < lineCount - 1 ? "\n" : "");

     return message;
  }

Given the code above, I would expect the output for a single line of text to look something like: "\\n\\n\\n\\nFoo". However, the output is "\\nFoo\\nFoo\\nFoo\\nFoo". Setting a break point in the code I see that textBox.GetLineText(index) for indices 0 through 3 returns "Foo" for each index even though "Foo" is only shown once in the TextBox control.

So I guess I really have two questions:

1) Why does GetLineText return a LineCount of 4 with every line having the same text, when only a single line of text (that fits on one line in the TextBox control) was entered by the user?

2) What is an easy way to work around this, keep the entered text centered in the TextBox control, and send the remote device the text message that will be displayed as seen by the user on the TextBox control?

Notes: I cannot simply remove duplicate lines of text and replace them with "\\n" as the user may have typed in the same text on multiple lines. Also, I could simply align the entered text to the vertical top instead of the vertical center. I have verified this works, but does not give a true WYSIWIG experience.

Answer 1

Looks like a bug in the method. You could work around this by either wrapping the textbox with another control that does the vertical centering or by extracting the lines via the text property.

    <StackPanel Orientation="Vertical" VerticalAlignment="Center">
    <TextBox AcceptsReturn="True" HorizontalAlignment="Stretch" HorizontalContentAlignment="Center" BorderThickness="0"> </TextBox>
    </StackPanel>

Answer 2

The following modified code from the method shown above solves the problem. I am still curious however if Microsoft has a bug with the textBox.GetLineText method.

      public static String AddNewLineCharsToMessage(TextBox textBox)
  {
     String message = String.Empty;

     if (textBox == null) return message;

     // Just assign the text if we have a single line message
     if (textBox.LineCount < 2)
        return textBox.Text;


     // Find the index for the first line that contains text displayed in the TextBox.
     // GetLineText(index) will return the text displayed/entered by the user for indices less
     // than the index of the line that the text is actually displayed on.  This seems to be
     // a bug to me, but I will workaround this Microsoft weirdness.

     // Find the index of first line that actually displays text by using the length of TextBox.Text
     Int32 firstTextLineIndex = 0;
     Int32 textLen = textBox.Text.Length;
     Int32 textLinesLen = 0;

     for (Int32 firstTextLine = textBox.LineCount - 1; firstTextLine >= 0; firstTextLine--)
     {
        textLinesLen += textBox.GetLineText(firstTextLine).Length;
        if (textLinesLen >= textLen)
        {
           firstTextLineIndex = firstTextLine;
           break;
        }
     }

     // First strip all the carriage returns and newline characters
     // so we don't have duplicate newline characters in the message.
     // Then add back in just the newline characters which is what the car
     // code uses to parse out the message to be displayed on each line.

     var textLines = new List<string>(5);
     int lineCount = Math.Min(textBox.LineCount, textBox.MaxLines);
     for (Int32 index = 0; index < lineCount; index++)
     {
        if (index < firstTextLineIndex)
           textLines.Add("");
        else  // if (textBox.GetLineText(index).Length > 0)
        {
           textLines.Add(textBox.GetLineText(index));
           textLines[index] = textLines[index].Replace("\r", "");
           textLines[index] = textLines[index].Replace("\n", "");
        }
     }

     message = String.Empty;
     for (Int32 index = 0; index < lineCount; index++)
        message += textLines[index] + (index < lineCount - 1 ? "\n" : "");

     return message;
  }