Question

I have the following code to take a screenshot. I am specifically not using UIGraphicsBeginImageContext, because before I found that this uses an awful lot of memory:

    CGSize size = activeView.frame.size;

    NSUInteger width = size.width;
    NSUInteger height = size.height;

    NSLog(@"BEFORE");

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    unsigned char *rawData = malloc(height * width * 4);
    memset(rawData,0,height * width * 4);

    NSUInteger bytesPerPixel = 4;
    NSUInteger bytesPerRow = bytesPerPixel * width;
    NSUInteger bitsPerComponent = 8;
    CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

    CGRect bounds;
    bounds.origin = CGPointMake(0,0);
    bounds.size = size;

    CGContextDrawImage(context, CGRectMake(0, 0, size.width, size.height), [self.topimage CGImage]);
    CGContextDrawImage(context, CGRectMake(0, 0, size.width, size.height), [bottomimage CGImage]);

    CGImageRef imageRef = CGBitmapContextCreateImage(context);
    UIImage *latest = [UIImage imageWithCGImage:imageRef scale:0.0 orientation:UIImageOrientationDownMirrored];

    [activeView.layer renderInContext:UIGraphicsGetCurrentContext()];

    CGImageRef imageRef2 = CGBitmapContextCreateImage(context);
    UIImage *latest2 = [UIImage imageWithCGImage:imageRef2 scale:0.0 orientation:UIImageOrientationDownMirrored];

    CGContextRelease(context);
    CGImageRelease(imageRef);
    CGImageRelease(imageRef2);

    NSLog(@"AFTER");

In between the ‘BEFORE’ and ‘AFTER’ NSLogs, these errors/warnings appear:

<Error>: CGContextSaveGState: invalid context 0x0
<Error>: CGContextSetAlpha: invalid context 0x0
<Error>: CGContextSaveGState: invalid context 0x0
<Error>: CGContextSetFillColorWithColor: invalid context 0x0
<Error>: CGContextAddRect: invalid context 0x0
<Error>: CGContextDrawPath: invalid context 0x0
<Error>: CGContextRestoreGState: invalid context 0x0
<Error>: CGContextSaveGState: invalid context 0x0
<Error>: CGContextGetBaseCTM: invalid context 0x0
<Error>: CGContextConcatCTM: invalid context 0x0
<Error>: CGContextSetBaseCTM: invalid context 0x0
<Error>: CGContextSaveGState: invalid context 0x0
<Error>: CGContextClipToRect: invalid context 0x0
<Error>: CGContextSetAlpha: invalid context 0x0
<Error>: CGContextSaveGState: invalid context 0x0
<Error>: CGContextSetFillColorWithColor: invalid context 0x0
<Error>: CGContextAddRect: invalid context 0x0
<Error>: CGContextDrawPath: invalid context 0x0
<Error>: CGContextRestoreGState: invalid context 0x0
<Error>: CGContextSaveGState: invalid context 0x0
<Error>: CGContextConcatCTM: invalid context 0x0
<Error>: CGContextConcatCTM: invalid context 0x0
<Error>: CGContextClipToRect: invalid context 0x0
<Error>: CGContextDrawImage: invalid context 0x0
<Error>: CGContextRestoreGState: invalid context 0x0
<Error>: CGContextRestoreGState: invalid context 0x0
<Error>: CGContextSetBaseCTM: invalid context 0x0
<Error>: CGContextRestoreGState: invalid context 0x0

Why is this happening?

Answer 1

[activeView.layer renderInContext:UIGraphicsGetCurrentContext()];

This line is the problem…you have no “current” context. Use context instead.