Since RichTextBox doesn't have a Images or Objects collection you have to go for the RTF formatting codes. All data of RichTextBox is stored as plain text with special formatting codes, this is exposed by the control through its RTF property. Learning this code language is essential if you want to read or change it, learning resources are easily available throughout the web, see for example this overview. RichTextBox uses more simplified rtf codes than several full-feature editors like MS Word etc, so it is usually beneficial to load data into a RTB before manipulating it, this will remove much redundant data.
Making a long story short, I found that it is necessary to search for rtf groups that start with either "pict" or "object" command. Knowing that groups may be nested you can't just find the first end-group char from there, you have to parse the string char by char while keeping count of grouping to find the end of those groups. Now you have enough information to remove that part of the string. Rtf may contain multiple picture/object groups so you have to do this until all are removed. Here is a sample function that return rtf string after removing those groups:
private string removeRtfObjects(string rtf)
{
//removing {\pict or {\object groups
string pattern = "\\{\\\\pict|\\{\\\\object";
Match m = Regex.Match(rtf, pattern);
while (m.Success) {
int count = 1;
for (int i = m.Index + 2; i <= rtf.Length; i++) {
//start group
if (rtf(i) == '{') {
count += 1;
//end group
} else if (rtf(i) == '}') {
count -= 1;
}
//found end of pict/object group
if (count == 0) {
rtf = rtf.Remove(m.Index, i - m.Index + 1);
break; // TODO: might not be correct. Was : Exit For
}
}
m = Regex.Match(rtf, pattern);
//go again
}
return rtf;
}
When should this be done? You have already mention Paste, there is also Insert, these can be trapped with the KeyDown event where you get the clipboard info and handle it accordingly. Setting e.Handled=True when you have handled the operation yourself signals that the control should not do any default processing for this key combination. This is also how you block pasting images without destroying the users clipboard. Example:
private void RichTextBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
//aware of Paste or Insert
if (e.Control && e.KeyCode == Keys.V || e.Shift && e.KeyCode == Keys.I) {
if (Clipboard.ContainsImage || Clipboard.ContainsFileDropList) {
//some images are transferred as filedrops
e.Handled = true;
//stops here
} else if (Clipboard.ContainsData(DataFormats.Rtf)) {
RichTextBox rtbox = new RichTextBox();
//use a temp box to validate/simplify
rtbox.Rtf = Clipboard.GetData(DataFormats.Rtf);
this.RichTextBox1.SelectedRtf = this.removeRtfObjects(rtbox.Rtf);
rtbox.Dispose();
e.Handled = true;
}
}
}
