1.UIColor生成图片

    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 100, 100, 100)];
    [self.view addSubview:imageView];
    UIColor *color = [UIColor redColor];
    
    UIGraphicsImageRenderer *re = [[UIGraphicsImageRenderer alloc] initWithSize:CGSizeMake(100, 100)];
    UIImage *image = [re imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) {
        [color setFill];
        [rendererContext fillRect:CGRectMake(0, 0, 100, 100)];
    }];
    
    imageView.image = image;

2.layer生成图片

    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 100, 100, 100)];
    [self.view addSubview:imageView];

    CAGradientLayer *layer = [CAGradientLayer layer];
    layer.frame = CGRectMake(0, 0, 100, 100);
    layer.locations = @[@(0.0), @(1.0)];
    layer.startPoint = CGPointMake(0, 0);
    layer.endPoint = CGPointMake(1, 0);
    layer.colors = @[(__bridge id)HexRGB(0x2ACAE6).CGColor,
                     (__bridge id)HexRGB(0x17D1A5).CGColor];
    UIGraphicsImageRenderer *re1 = [[UIGraphicsImageRenderer alloc] initWithSize:CGSizeMake(100, 100)];
    UIImage *image1 = [re1 imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) {
        [layer renderInContext:rendererContext.CGContext];
    }];


    imageView.image = image1;

3.绘制文本

    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 100, 100, 100)];
    [self.view addSubview:imageView];
    CGSize size = CGSizeMake(100, 100);

    UIGraphicsImageRendererFormat *format = [[UIGraphicsImageRendererFormat alloc] init];
    format.scale = 0;
    format.opaque = NO;
    UIGraphicsImageRenderer *render = [[UIGraphicsImageRenderer alloc] initWithSize:size format:format];
    UIImage *markImage = [render imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) {
        [[UIColor blackColor] set];
        [@"123123123" drawAtPoint:CGPointZero
          withAttributes:@{NSFontAttributeName: [UIFont systemFontOfSize:19 weight:(UIFontWeightMedium)],
                           NSForegroundColorAttributeName: [UIColor blackColor]}];
    }];
    imageView.image = markImage;

4.图片绘制圆角

    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 100, 100, 100)];
    [self.view addSubview:imageView];

    UIImage *image2 = [UIImage imageNamed:@"change.jpeg"];
    UIGraphicsImageRendererFormat *format1 = [[UIGraphicsImageRendererFormat alloc] init];
    format.scale = [UIScreen mainScreen].scale;
    format.opaque = NO;
    UIGraphicsImageRenderer *render1 = [[UIGraphicsImageRenderer alloc] initWithSize:image2.size format:format1];
    UIImage *circleImage = [render1 imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) {
        CGContextRef context = rendererContext.CGContext;
        CGRect rect = CGRectMake(0, 0, image2.size.width, image2.size.height);
        CGContextBeginPath(context);
        CGContextAddEllipseInRect(context, rect);
        CGContextClosePath(context);
        CGContextClip(context);
        [image2 drawInRect:rect];
    }];
    imageView.image = circleImage;

5.UIColor生成图片并切圆角

- (UIImage *)createImageWithColor:(UIColor *)color size:(CGSize)size radius:(CGFloat)radius {
    CGRect rect = CGRectMake(0.0f, 0.0f, size.width, size.height);
    
    UIGraphicsImageRendererFormat *format = [[UIGraphicsImageRendererFormat alloc] init];
    format.scale = [UIScreen mainScreen].scale;
    format.opaque = NO;
    UIGraphicsImageRenderer *render = [[UIGraphicsImageRenderer alloc] initWithSize:size format:format];
    UIImage *image = [render imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) {
        CGContextRef context = rendererContext.CGContext;
        CGContextSetFillColorWithColor(context, color.CGColor);
        UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:radius];
        CGContextAddPath(context, path.CGPath);
        CGContextFillPath(context);
    }];

    return image;
}