Move NSView around until it hits a border - objective-c

Question

In a Cocoa-based App i'm having a canvas for drawing, inherited from NSView, as well as a rectangle, also inherited from NSView. Dragging the rectangle around inside of the canvas is no problem:
-(void)mouseDragged:(NSEvent *)theEvent {
NSPoint myOrigin = self.frame.origin;
[self setFrameOrigin:NSMakePoint(myOrigin.x + [theEvent deltaX],
myOrigin.y - [theEvent deltaY])];
}
Works like a charm. The issue i'm having now: How can i prevent the rectangle from being moved outside the canvas?
So, first of all i would like to fix this just for the left border, adapting the other edges afterwards. My first idea is: "check whether the x-origin of the rectangle is negative". But: once it is negative the rectangle can't be moved anymore around (naturally). I solved this with moving the rectangle to zero x-offset in the else-branch. This works but it's ... ugly.
So i'm little puzzled with this one, any hints? Definitely the solution is really near and easy. That easy, that i cannot figure it out (as always with easy solutions ;).
Regards
Macs

Answer 1

I'd suggest not using the deltaX and deltaY; try using the event's location in the superview. You'll need a reference to the subview.
// In the superview
- (void)mouseDragged:(NSEvent *)event {
NSPoint mousePoint = [self convertPoint:[event locationInWindow]
fromView:nil];
// Could also add the width of the moving rectangle to this check
// to keep any part of it from going outside the superview
mousePoint.x = MAX(0, MIN(mousePoint.x, self.bounds.size.width));
mousePoint.y = MAX(0, MIN(mousePoint.y, self.bounds.size.height));
// position is a custom ivar that indicates the center of the object;
// you could also use frame.origin, but it looks nicer if objects are
// dragged from their centers
myMovingRectangle.position = mousePoint;
[self setNeedsDisplay:YES];
}
You'd do essentially the same bounds checking in mouseUp:.
UPDATE: You should also have a look at the View Programming Guide, which walks you through creating a draggable view: Creating a Custom View.
Sample code that should be helpful, though not strictly relevant to your original question:
In DotView.m:
- (void)drawRect:(NSRect)dirtyRect {
// Ignoring dirtyRect for simplicity
[[NSColor colorWithDeviceRed:0.85 green:0.8 blue:0.8 alpha:1] set];
NSRectFill([self bounds]);
// Dot is the custom shape class that can draw itself; see below
// dots is an NSMutableArray containing the shapes
for (Dot *dot in dots) {
[dot draw];
}
}
- (void)mouseDown:(NSEvent *)event {
NSPoint mousePoint = [self convertPoint:[event locationInWindow]
fromView:nil];
currMovingDot = [self clickedDotForPoint:mousePoint];
// Move the dot to the point to indicate that the user has
// successfully "grabbed" it
if( currMovingDot ) currMovingDot.position = mousePoint;
[self setNeedsDisplay:YES];
}
// -mouseDragged: already defined earlier in post
- (void)mouseUp:(NSEvent *)event {
if( !currMovingDot ) return;
NSPoint mousePoint = [self convertPoint:[event locationInWindow]
fromView:nil];
spot.x = MAX(0, MIN(mousePoint.x, self.bounds.size.width));
spot.y = MAX(0, MIN(mousePoint.y, self.bounds.size.height));
currMovingDot.position = mousePoint;
currMovingDot = nil;
[self setNeedsDisplay:YES];
}
- (Dot *)clickedDotForPoint:(NSPoint)point {
// DOT_NUCLEUS_RADIUS is the size of the
// dot's internal "handle"
for( Dot *dot in dots ){
if( (abs(dot.position.x - point.x) <= DOT_NUCLEUS_RADIUS) &&
(abs(dot.position.y - point.y) <= DOT_NUCLEUS_RADIUS)) {
return dot;
}
}
return nil;
}
Dot.h
#define DOT_NUCLEUS_RADIUS (5)
#interface Dot : NSObject {
NSPoint position;
}
#property (assign) NSPoint position;
- (void)draw;
#end
Dot.m
#import "Dot.h"
#implementation Dot
#synthesize position;
- (void)draw {
//!!!: Demo only: assume that focus is locked on a view.
NSColor *clr = [NSColor colorWithDeviceRed:0.3
green:0.2
blue:0.8
alpha:1];
// Draw a nice border
NSBezierPath *outerCirc;
outerCirc = [NSBezierPath bezierPathWithOvalInRect:
NSMakeRect(position.x - 23, position.y - 23, 46, 46)];
[clr set];
[outerCirc stroke];
[[clr colorWithAlphaComponent:0.7] set];
[outerCirc fill];
[clr set];
// Draw the "handle"
NSRect nucleusRect = NSMakeRect(position.x - DOT_NUCLEUS_RADIUS,
position.y - DOT_NUCLEUS_RADIUS,
DOT_NUCLEUS_RADIUS * 2,
DOT_NUCLEUS_RADIUS * 2);
[[NSBezierPath bezierPathWithOvalInRect:nucleusRect] fill];
}
#end
As you can see, the Dot class is very lightweight, and uses bezier paths to draw. The superview can handle the user interaction.