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ch text component is a memo control that supports rich text formatting. That is, you can change the formatting of individual characters, words, or paragraphs. It includes a Paragraphs property that contains information on paragraph formatting. Rich text controls also have printing and text-searching capabilities.
By default, the rich text editor supports
- Font properties, such as typeface, size, color, bold, and italic format
- Format properties, such as alignment, tabs, indents, and numbering
- Automatic drag-and-drop of selected text
- Display in both rich text and plain text formats.
(Set PlainText to True to remove formatting)
type TNotifyEvent = procedure(Sender: TObject) of object;
property OnChange: TNotifyEvent;
4. Is it the event I want - ie [OnChange] Event - the right one?
Live dangerously, let’s give it a go and see...by testing our assumptions out:
So I wrote my first [OnChange] event:
- Create a New application
- place on it one RichEdit (RichEdit1) and one Edit control (Edit1)
- Code the [OnChange] for the RichEdit1 control like this:
procedure TForm1.RichEdit1Change(Sender: TObject);
begin
TRichEdit(Sender).Tag := TRichEdit(Sender).Tag + 1;
Edit1.Text := ''''Tag='''' + IntToStr(TRichEdit(Sender).Tag);
end;
In this case the Sender object is the RichEdit being changed. The code basically uses the RichEdit''''s Tag variable (initially 0) as a handy Control specific variable. Everytime the [OnChange] event is called, it increases the Tag by 1, and display its value in an Edit Control as Text. You should pre-set the RichEdit control with some text in it, otherwise the following may be confusing!
- Compile and Run...
- Click in the Control. Nothing...
- Move around in it using CursorKeys... Nothing...
- Click outside the control.. and then back inside.. Nothing...
- Press the [Space Bar].. Tag=1...
- Press [Backspace].. Tag=2...
- Press return.. Tag=3..
- Select some text.. No change..
- CTRL-C some text.. No change..
- CTRL-X some text.. Tag=4..
- CTRL-V some text.. Tag=5..
As it looked good so far I then added to the Form1.OnShow event:
RichEdit1.Lines.LoadFromFile(''''c:\winzip.log''''); {Just a plain text file hanging around }
to see what happened. And guess what - an [OnChange] event was called sometime and "Tag=1" was displayed in the Edit control as the proof when the Form appears for the first time. So we can see that procedures do call Events that apply to what they are doing.
5. What happens in Syntax Highlighting anyhow?
Watch carefully in the Delphi Editor. Now try and reproduce it. Open a WordPad (since WordPad is a souped up RichEdit basically). Read in a source file (e.g any Unit1.pas) and do syntax highlighting manually:
- Select a token
- Manipulate it using the buttons provided to change Font, Size, Color, and Bold
- Move onto the next token
- Goto 1
So therefore in [OnChange] we''''ll try and write code to reproduce what we have done manually.
6. Which text do I want.. and where do I get it ?
Hunting through the Delphi Helpfile on RichEdit controls we find that the actual text information in the RichEdit control is stored (or rather can be accessed from) either:
RichEdit.Text
Text contains a text string associated with the control.
TCaption = type string;
property Text: TCaption;
Description
Use the Text property to read the Text of the control or specify a new string for the Text value. By default, Text is the control name. For edit controls and memos, the Text appears within the control. For combo boxes, the Text is the content of the edit control portion of the combo box.
RichEdit.Lines
Lines contains the individual lines of text in the rich text edit control.
property Lines: TStrings;
Description
Use Lines to manipulate the text in the rich text edit control on a line by line basis. Lines is a TStrings object, so TStrings methods may be used for Lines to perform manipulations such as counting the lines of text, adding lines, deleting lines, or replacing the text in lines.
To work with the text as one chunk, use the Text property. To manipulate individual lines of text, the Lines property works better.
Now Lines seemed to be what I wanted - after all I wanted the Syntax highlighting to work on a line by line basis. So let’s have a look at whats been changed.
Oh.. look at what? How can I tell which line is the one that is changed?
Unlike some Events, the [OnChange] isn''''t passed any variable''''s save the identity of the RichEdit control affected. The RichEdit Control doesn''''t have a runtime variable that tells us either. The only variables are the SelStart and SelLength - but their about selecting text aren''''t they? I just want to know what line I''''m on :-(
It was about then that I re-read the information on the Sel??? properties, and recalled my "concept" code. Selection - I realised - was the name of the game. By manipulating these variables I could reproduce what I was doing manually - selecting text - as program code. Once selected you can then manipulate the attributes of the selected text through the SelAttributes structure.
Let’s get familiar with these variables (in Summary)
.
SelStart
Position of the Cursor, or the beginning of the selected text
SelLength
0 if SelStart = Cursor Pos, or length of selected Text
SelText
empty if no text selected, or actual text selected
SelAttribute
Default attributes if I was to start typing at the Cursor position OR the actual attributes of the selected text
There is actually no other way to access the attributes of the text already in the Control than by programmatically accessing them via manipulating Sel variables (*if you stick to using the defined properties and methods).
In the end RichEdit.Text and RichEdit.Lines are just plain old strings - not really "rich" at all. The other thing to note is that SelStart is a 0-based index on the first character of RichEdit.Text - so it looks like Richedit.Line is out the door.
7. Okay implement: Select a Token
Basically I wanted to start at the beginning of the line, send just that line to PasCon, and read it back in and replace the current line with the result. Trouble is RichEdit doesn''''t give you access to the ''''RTF'''' representation of a single line. Plus I still can''''t tell when the beginning or end of the line is. Since the latter seems to be a nagging problem, we better fix that first - trouble is: How?
When all else fails - WinAPI calls of course.
Most visual controls in Delphi are in fact just native Windows controls encapsulate as Delphi types. You can still use Windows API functions to access the control underneath. This was it is possible to access information not accessable per Delphi public Properties, Method or Events. Time to delve through Win32.HLP and see what it has to say about RichEdit controls. Its stored in C:/Program Files/Borland/Delphi 3.0/Help if you don''''t have a shortcut to it.
Open Win32.HLP -> [ Contents ] -> [ RichEdit controls ] -> [ Rich Edit Controls ]
I spent some time getting to know the "full" capabilites of the RichEdit control hidden behind Delphi''''s implementation of it. Much of what I learned came in handy later on (as you''''ll see) and as a result I derived my second two Delphi Rules:
Delphi Rule #2: If your Project hinges on the capabilities of a certain control - make sure you know everthing about it - from the beginning.
Delphi Rule #3: "Reference" is not the same as "Summary" (also known as Win32.HLP Rule#1)
Eventually I discovered the key in the [ Rich Edit Control Reference ] under "Lines and Scrolling". I had thought this page was simply a summary of the messages discussed in the preceding help pages. Actually it included a number of extra messages not discussed elsewhere - the exact ones I was after!
Lines and Scrolling
EM_LINEFROMCHAR - give them a 0-based index and they''''ll return the line
EM_LINEINDEX - give them a line and you get the index of the first character
EM_LINELENGTH - give them a line and you get the length of the line
So lets start coding.
(NB: To use the constants (EM-?) you''''ll have to manually add RichEdit in the uses clause)
procedure TForm1.RichEdit1Change(Sender: TObject);
var WasSelStart,Row,BeginSelStart,EndSelStart: Integer;
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