Question

The context is that I am trying to plot a series of temperatures as a graph.

At the moment my application works as follows (as i understand it):

The application opens, openfile is used which initialises my document class this reads the modified csv file into an NSString “fileContents” which I then separate into an array of strings, each string containing the value without separaters or whitespace. As follows:

NSArray *temps = [fileContents componentsSeparatedByCharactersInSet: [NSCharacterSet characterSetWithCharactersInString:@"\n|\r"]];

After that I initialise my custom view, the TemperatureGraph class, and immediately pass it the array which becomes the currentlog seen in the code below. Instance id is current.

Finally I invoke:

[current drawpath];

Which is the instance method below:

- (void) drawpath
{
    NSBezierPath *program = [NSBezierPath bezierPath];
    NSPoint st = NSMakePoint(0, 0);

    [program moveToPoint:st];
    [program setLineWidth:10];
    [program setLineCapStyle:NSRoundLineCapStyle];
    [[NSColor blueColor] setStroke];
    [program stroke];

    NSUInteger a, b;
    a = [currentlog count];
    b = 0;
    while (b <= a) {
        NSPoint new;
        float x;
        x = 5 * b;

        new = NSMakePoint(x, [[currentlog objectAtIndex:b] floatValue]);
        [program lineToPoint:new];
        [program stroke];
        b += 6;
    }
}

Why won’t it work? Definition of won’t work: Application compiles and runs but I have a blank window.

Also please point out any rookie errors that are in there but don’t affect code, as I am still in the learning stages here.

Answer 1

Drawing doesn’t happen unless you have an active graphics context. I’m assuming the drawpath method above is inside an NSView subclass – well in there you need to override a method called drawRect: – it may even have been added in as a stub when you made the subclass?

Cocoa calls this method when it is time for the view to draw itself. This means that, when it is being called, a graphics context will be set up and and drawing code you do will actually appear on the screen.

Simply call your drawpath method from inside drawRect: and you should see your lines.

The general point to remember is that you don’t call any drawing code yourself (except from within drawRect:– you either mark a view as needing display ([myView setNeedsDisplay:YES];, or let the system do that itself.