iOS视图生成图片

iOS10以上

 UIGraphicsImageRendererFormat *format = [[UIGraphicsImageRendererFormat alloc] init];
    format.prefersExtendedRange = YES;
    UIGraphicsImageRenderer *renderer = [[UIGraphicsImageRenderer alloc] initWithSize:self.imageView.size format:format];
    __weak typeof(self) weakSelf = self;
    UIImage *tmpImage = [renderer imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) {
        return [weakSelf.imageView.layer renderInContext:rendererContext.CGContext];
    }];

iOS 10以下的方式

UIGraphicsBeginImageContextWithOptions(self.selectedImage.size, NO, self.selectedImage.scale);
    [self.selectedImage drawAtPoint:CGPointZero];
    CGFloat scale = self.selectedImage.size.width / self.imageView.width;
    CGContextScaleCTM(UIGraphicsGetCurrentContext(), scale, scale);
    [self.imageView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *tmpImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

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