How to create a UIImage with a transparent background

Question

I am dynamically creating a (drawing my own custom) UIImage for the 'UIImageView' property on a UITableViewCell.

When a user selects the tableView cell, the cell background turns blue but my custom UIImage background does not - it remains white (so it is painfully clear I've got an image sitting there). I've tried various drawing approaches

// when I create the cell
cell.imageView.backgroundColor = [UIColor clearColor];
cell.imageView.opaque = NO;

// 1. when I create the UIImage - clearColor background
CGContextSetFillColorWithColor(context, [UIColor clearColor].CGColor);
CGContextFillRect(context, rect);

// 2. when I create the UIImage - clear background
CGContextClearRect(context, rect);

but in both of these approaches, the background is black. The only thing that seems to work is to finishing creating the image and then apply create a 2nd image with 'CGImageCreateWithMaskingColors' based on the first image - masking out the background.

Is there a way I can "paint" a transparent background in the first place?

Answer 1

在设置图像上下文时，请确保将NO传递给UIGraphicsBeginImageContextWithOptions函数的opaque参数。