Cocoa Internals/Memo

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TMemo widgetset is implemented over NSTextView and NSScrollView

NSTextView

By default NSTextView is designed to be constantly word-wrapped. Disabling word-wrapping could be quite complicated from a start due to odd-default values chosen by Apple, as well as complex (yet flexible) Text Layout system.

  • NSTextView is a "cocoa" control, however it's not drawing the text by it's own it's also using:
  • NSTextContainer. Both NSTextContainer and NSTextView settings influence on how the text is rendered in the end.

The example shows, of creating NSTextView that automatically resizes itself horizontally. However NSTextView doesn't provide its own scrollbars, thus no scrollbars would be seen.

procedure TForm1.FormShow(Sender: TObject);
var
  txt : NSTextView;
begin
  txt := NSTextView.alloc.initWithFrame(NSMakeRect(10,ClientHeight-10-50,50,50));
 
  txt.setFont(NSFont.systemFontOfSize(NSFont.systemFontSizeForControlSize(NSRegularControlSize)));
 
  // making the maximum size - maximum!
  // 10000000 is a "constant" could be found in Apple documentation
  txt.setMaxSize( NSMakeSize(10000000, 10000000));
  // preventing textContainer from following the width of NSTextView
  txt.textContainer.setWidthTracksTextView(false);
  // making TextContainer large enough.
  txt.textContainer.setContainerSize ( NSMakeSize( 10000000, 1024));
  // making NSTextView to resize automatically to the text boundries (max width)
  txt.setHorizontallyResizable(true);
 
  NSView(Self.Handle).addSubView(txt);
end;

The next step is actually to embed NSTextView into ScrollView (as a documentView).

Inserting into Scroll View

The process is straight-forward - allocate scroll view, use NSTextView as it's document view

procedure TForm1.FormShow(Sender: TObject);
var
  txt : NSTextView;
  sc  : NSScrollView;
begin
  txt := NSTextView.alloc.initWithFrame(NSMakeRect(10,ClientHeight-10-50,50,50));
 
  txt.setMaxSize( NSMakeSize(10000000, 10000000));
  txt.textContainer.setWidthTracksTextView(false);
  txt.textContainer.setContainerSize ( NSMakeSize( 10000000, 1024));
  txt.setHorizontallyResizable(true);
 
  // allocating scroll view and placing NSTextView inside
  sc := NSScrollView.alloc.initWithFrame(NSMakeRect(10,ClientHeight-10-150,150,150));
  sc.setHasVerticalScroller(true);
  sc.setHasHorizontalScroller(true);
  sc.setAutohidesScrollers(true);
  sc.setDocumentView(txt);
 
  NSView(Self.Handle).addSubView(sc);
end;

Now text-view and scrollbars would act as expected.

Line padding oddity

By default, there's 5 pixels padding between border of NSTextView and left-side of the text.

It's possible to decrease it, however, setting it to zero is causing a very weird and unpleasant glitch.

var
  txt : NSTextView;
  sc  : NSScrollView;
begin
  txt := NSTextView.alloc.initWithFrame(NSMakeRect(10,ClientHeight-10-50,50,50));
 
  txt.setMaxSize( NSMakeSize(10000000, 10000000));
  txt.textContainer.setWidthTracksTextView(false);
  txt.textContainer.setContainerSize ( NSMakeSize( 10000000, 1024));
  txt.setHorizontallyResizable(true);
 
  // setting this value to 0 is causing the problem.
  txt.textContainer.setLineFragmentPadding(0);
 
  sc := NSScrollView.alloc.initWithFrame(NSMakeRect(10,ClientHeight-10-150,150,150));
  sc.setHasVerticalScroller(true);
  sc.setHasHorizontalScroller(true);
  sc.setAutohidesScrollers(true);
  sc.setDocumentView(txt);
 
  NSView(Self.Handle).addSubView(sc);
end;

Now. Everytime a new line break is added to the end of the text the view scrolls to the top (while having cursor at the bottom).

Either by pressing Enter on keyboard having cursor at the end of the text. Or by inserting a line break at the end of the text programmatically.


The only way to avoid the problem is to have Fragment padding set to a value greater than zero.

See Also