how to customize the input of drawRect - objective-c

Question

Here's my drawRect code:
- (void)drawRect:(CGRect)rect {
if (currentLayer) {
[currentLayer removeFromSuperlayer];
}
if (currentPath) {
currentLayer = [[CAShapeLayer alloc] init];
currentLayer.frame = self.bounds;
currentLayer.path = currentPath.CGPath;
if ([SettingsManager shared].isColorInverted) {
currentLayer.strokeColor = [UIColor blackColor].CGColor;
} else {
currentLayer.strokeColor = [UIColor whiteColor].CGColor;
}
currentLayer.strokeColor = _strokeColorX.CGColor;
currentLayer.fillColor = [UIColor clearColor].CGColor;
currentLayer.lineWidth = self.test;
currentLayer.contentsGravity = kCAGravityCenter;
[self.layer addSublayer:currentLayer];
//currentLayer.position = CGPointMake(CGRectGetMidX(self.frame), CGRectGetMidY(self.frame));
}
//[currentPath stroke];
}
"The portion of the view’s bounds that needs to be updated"
That's from the apple dev docs.
I am dealing with a UIView and a device called a slate -the slate has the ability to record pencil drawings to my iOS app. I managed to get it working on the entire view. But, I dont want the entire view to be filled with the slate input. Instead, I'd like to modify the UIView to have a height of phonesize - 40px; Makes sense?

Answer 1

I found out if I set the frame that I have as currentLayer to new bounds the screen that can be drawn on is resized accordingly.

Answer 2

I think you’re mixing up the meaning of the various rectangles in UIView. The drawRect parameter designates a partial section of the view that needs to be redrawn. This can be that you called setNeedsDisplay(rect), or this can be because iOS thinks it needs to be redrawn (e.g. because your app‘s drawings were ignored because the screen was locked, and now the user unlocked the screen and current drawings are needed).
This rectangle has nothing to do with the size at which your contents are drawn. The size of the area your view is drawn in is controlled by its frame and bounds, the former of which is usually controlled using Auto Layout (i.e. layout constraint objects).
In general, while in drawRect, you look at the bounds of your view to get the full rectangle to draw in. The parameter to drawRect, on the other hand, is there to allow you to optimize your drawing to only redraw the parts that actually changed.
Also, it is in general a bad idea to manipulate the view and layer hierarchies from inside drawRect. The UIView drawing mechanism expects you to only draw your current view‘s state in there. Since it recursively walks the list of views and subviews to call drawRect, you changing the list of views or layers can cause weird side effects like views being skipped until the next redraw.
Create and add new layers in your state-changing methods or event handling methods, and position them using auto layout or from inside layoutSubviews.