NSView and NSScrollView: button that disappears and reappears on another position

Question

I am at the 17th chapter of Aaron's Cocoa programming for Mac os X, and in the example he embeds a NSView in a NSScrollView.
For exercise I also have added a NSButton programmatically to the view.
The problem is a strange behaviour of the button, which firstly appears on the scroll view, but when I move down the vertical scroller, the button disappears and reappears in the bottom of the scroll view.Since this may be confusing (and also hard to explain), I have made a video to better describe the problem:

http://tinypic.com/player.php?v=k1sacz&s=6

I have subclassed NSView and called the class StretchView (as the book says).
This is the code:

#import <Cocoa/Cocoa.h>

@interface StretchView : NSView
{
@private
    NSBezierPath* path;
}

- (NSPoint) randomPoint;
- (IBAction) click : (id) sender;

@end


#import "StretchView.h"

@implementation StretchView

- (void) awakeFromNib
{
    // Here I add the button
    NSView* view=self;
    NSButton* button=[[NSButton alloc] initWithFrame: NSMakeRect(10, 10, 200, 100)];
    [button setTitle: @"Click me"];
    [button setTarget: self];
    [button setAction: @selector(click:)];
    [view addSubview: button];
}

- (IBAction) click:(id)sender
{
    NSLog(@"Button clicked");
}

- (void) drawRect:(NSRect)dirtyRect
{
    NSRect bounds=[self bounds];
    [[NSColor greenColor] set];
    [NSBezierPath fillRect: bounds];
    [[NSColor whiteColor] set];
    [path fill];
}

- (id) initWithFrame:(NSRect)frameRect
{
    self=[super initWithFrame: frameRect];
     if(self)
    {
        // here i dra some random curves to the view
        NSPoint p1,p2;
        srandom((unsigned int)time(NULL));
        path=[NSBezierPath bezierPath];
        [path setLineWidth: 3.0];
        p1=[self randomPoint];
        [path moveToPoint: p1];
        for(int i=0; i<15; i++)
        {
            p1=[self randomPoint];
            p2=[self randomPoint];
            [path curveToPoint: [path currentPoint] controlPoint1: p1 controlPoint2: p2 ];
            [path moveToPoint: p1];
        }
        [path closePath];
    }
    return self;
}

- (NSPoint) randomPoint
{
    NSPoint result;
    NSRect r=[self bounds];
    result.x=r.origin.x+random()%(int)r.size.width;
    result.y=r.origin.y+random()%(int)r.size.height;
    return result;
}

@end

Questions:

1) Why does the button disappear - reappear and how to avoid this problem?
2) Why are the curves filled in white? I wanted to draw them as tiny lines, not filled.

Answer 1

Part 1:

What it looks like is that the scroll view isn't updating its scroll bars to where the view is actually scrolled. (Upon launch, it seems like it's showing that the view is scrolled down to the bottom left already, even when the scroll bar is at the top).

I can only ask, for now, what OS are you running? It works perfectly for me on Mountain Lion, unless I didn't duplicate your code correctly.

---

Part 2:

The paths are filled because you used [path fill] in drawRect. Use [path stroke] instead, for strokes.