UIView子类不能从黑色背景改变

Question

I've created a subview of UIView to make some drawings - the drawings work fine in the drawRect method of my subclass, however, I cannot change the background color of the view. A little googling tells me I haven't set the frame for the view, but I'm not entirely sure how to do this. I tried two things:

I create the view in Storyboard and add it to my view controller, then declare it as a property in the header file and link them up. I synthesize the property at the top of the implementation file and in the viewDidLoad method, I add:

[myView setBackgroundColor: [UIColor whiteColor]];

The view's background is still black.

I also tried:

ViewSubclass *v = [[ViewSubclass alloc] initWithFrame: self.view.frame];
v.backgroundColor = [UIColor whiteColor];
myView = v;

To no avail.

What am I doing wrong?

UPDATE: This is the code I use to draw in the view, in case there's something going on there!

- (void)drawRect:(CGRect)rect {
CGFloat height = self.bounds.size.height;
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClearRect(context, rect);
CGContextSetFillColorWithColor(context, [UIColor grayColor].CGColor);
CGFloat barWidth = 30;
int count = 0;
for (NSNumber *num in samples) {
    CGFloat x = count * (barWidth + 10);
    CGRect barRect = CGRectMake(x, height - ([num floatValue] * height), barWidth, [num floatValue] * height);
    CGContextAddRect(context, barRect);
    count++;
}
CGContextFillPath(context);
}

It just creates a set of bars in the screen, of different heights.

Answer 1

CGContextClearRect From the docs:

If the provided context is a window or bitmap context, Quartz effectively clears the rectangle. For other context types, Quartz fills the rectangle in a device-dependent manner. However, you should not use this function in contexts other than window or bitmap contexts.

It might be that this clearing clears your entire view with no regard to the background color you set

Answer 2

I can t add comments due my low lvl, but the question springs to mind, have you added to your UIView to viewcontroller?

like

[self.view addSubview:v];

EDIT:

I'm sorry I had understood that the second option was added to the view that pragmatically.

Answer 3

Are you adding the view in the header file? If so you might need to be sure the frame's coordinates are visible and that the view is on top, also make the new view slightly smaller to see if it is actually being created:

UIView *myView = [[UIView alloc] initWithFrame:CGRectMake(0,0,100,100)];
[self.view addSubview: myView];
[self.view bringSubviewToFront:myView];

You can also change the main view background color to see if the new view is actually being created. For example:

[self.view setBackgroundColor:[UIColor grayColor]];

If the color is changing for your main view then the problem is that your new view is not being or brought to the front. Let us know how it goes!

Answer 4

At the point where do

[myView setBackgroundColor: [UIColor whiteColor]];

check to see if myView is not nil in the debugger