Women in Technology

Article:		Building a Scratch Pad with Cocoa
Subject:		How to use scrolling in a NSView Subclass
Date:		2001-12-31 07:06:24
From:		zeus
I tri to make a very simple sofware, and in that sofware I need to scroll the view. Here is my code: -(void)mouseDown:(NSEvent *) theEvent{ NSPoint loc = [theEvent locationInWindow]; loc.x -= [self frame].origin.x; loc.y -= [self frame].origin.y; [self scrollPoint:loc]; [self setNeedsDisplay:YES]; } I'm using a methode scrollPoint:aPoint from the NSView Class but i can't hardly get a scroll. I'm sure that i'm going into this method because when I ran my soft in debugger mode I get the right coordinates of the point "loc". Does anyone have an idea ?

Showing messages 1 through 2 of 2.

• I'm going to try to say what's going on
  2002-01-01 19:35:03  psheldon [View]
  
  
  Here's what I think is going on. If I'm right, I agree with you, I'm confused as you why it doesn't work.
  loc, an NSPoint gets assigned, at first, the location of the mousedown. Then, with a c assignment, you take that location relative to the origin and use that for loc. Then scrollPoint, a method of NSView, is supposed to scroll the view. After, setNeedsDisplay, forces a redraw of the view.
  It seems that if all that I said above is true, this thing you made should work.
  One candidate to make it work would have you go through reading all the methods to see where this thing falls short of the above expectations. That candidate course of action, however, doesn't break the problem into chunks.
  A question, however, came out of the blue for me. WIth mousedown so engaged what is the source of the drawing that you are scrolling? If you have the drawing happening in the NSView method (is it drawrect?) then that happens after setNeedsDisplay and so the scrolling can't move it.
  I'm thinking that it's possible that scrolling moves screenbits and you don't use setNeedsDisplay to force a draw after scrolling . Is that so?
  There's a chunk to find out !
  Maybe you could make an additional button and boolean and have a multiuse mousedown and have some sense of conceptual victory. The button and boolean would have two states, one for mousedown draws and other for it scrolls.
  Well, I'm sorry, I don't get much more coherent today, New Year's Day. I'm exhausted. I don't dare experiment with my ideas on this today.
  Soon (Friday) I go off a week to visit my mother without internet access.
• I'm going to try to say what's going on
  2002-01-03 08:02:33  zeus [View]
  
  
  As you say I'm drawing in a drawRect method but could you give me something concrete because I'm almost lost.
  And an other thing : I cannot access the NSView.m file that would let me see where the things are going wrong.
  In any case thanks for the help.