Customizing Table View Cells: Mastering Gradients and Selection States

Understanding Table View Cells and Customization

Table view cells are a crucial component of iOS development, allowing developers to create custom layouts for their table views. When working with table view cells, it’s common to encounter various challenges, such as animating cell selection or applying gradients to the cell background.

In this article, we’ll delve into the world of table view cells and explore how to customize the appearance of these cells, including removing a gradient when the cell is selected.

Creating Custom Table View Cells

To create a custom table view cell, you’ll need to subclass UITableViewCell and override its drawContentView: method. This method allows you to draw your own custom content within the cell.

- (void)drawContentView:(CGRect)r {
    // Code for drawing the custom content goes here...
}

Applying Gradients to Table View Cells

To apply a gradient to a table view cell, you can use the CGGradient and CGContextDrawLinearGradient functions. Here’s an example of how to create a simple gradient:

- (void)drawContentView:(CGRect)r {
    // ...

    size_t num_locations = 2;
    CGFloat locations[2] = {0.0, 1.0};
    CGFloat components[8] = {0.9f, 0.9f, 0.9f, 0.7f,
                             1.0f, 1.0f, 1.0f, 1.0};

    CGColorSpaceRef myColorspace = CGColorSpaceCreateDeviceRGB();
    CGGradientRef myGradient = CGGradientCreateWithColorComponents(myColorspace, components, locations, num_locations);

    CGPoint startPoint, endPoint;
    startPoint.x = 0;
    startPoint.y = self.frame.size.height;
    endPoint.x = 0;
    endPoint.y = self.frame.size.height - 15; // Adjust the gradient height to your liking

    CGContextDrawLinearGradient(context, myGradient, startPoint, endPoint, 0);
    CGGradientRelease(myGradient);

    // ...
}

Removing the Gradient When the Cell is Selected

The issue at hand is that the gradient remains visible when the cell is selected. To remove the gradient, we need to conditionally draw it based on the selected state of the cell.

One way to achieve this is by wrapping the gradient drawing code in an if (!self.selected) statement:

- (void)drawContentView:(CGRect)r {
    // ...

    if (!self.selected) {
        size_t num_locations = 2;
        CGFloat locations[2] = {0.0, 1.0};
        CGFloat components[8] = {0.9f, 0.9f, 0.9f, 0.7f,
                                 1.0f, 1.0f, 1.0f, 1.0};

        CGColorSpaceRef myColorspace = CGColorSpaceCreateDeviceRGB();
        CGGradientRef myGradient = CGGradientCreateWithColorComponents(myColorspace, components, locations, num_locations);

        CGPoint startPoint, endPoint;
        startPoint.x = 0;
        startPoint.y = self.frame.size.height;
        endPoint.x = 0;
        endPoint.y = self.frame.size.height - 15; // Adjust the gradient height to your liking

        CGContextDrawLinearGradient(context, myGradient, startPoint, endPoint, 0);
        CGGradientRelease(myGradient);

        // ...
    }

    // ...
}

Alternative Solution: Using a UIImageView

As suggested in the original question, another approach is to use a UIImageView instead of drawing the gradient directly. This allows you to easily switch between different gradient images based on the cell’s selected state.

- (void)drawContentView:(CGRect)r {
    // ...

    UIImage *gradientImage = [UIImage gradientWithColors:[UIColor colorWithRed:77.f/255.f green:103.f/255.f blue:155.f/255.f alpha:1] topColor:[UIColor clearColor] bottomColor:[UIColor whiteColor]];

    UIImageView *gradientView = [[UIImageView alloc] initWithImage:gradientImage];
    gradientView.frame = self.bounds;
    [self.contentView addSubview:gradientView];

    // ...
}

- (UIImage *)gradientWithColors:(UIColor *)startColor topColor:(UIColor *)topColor bottomColor:(UIColor *)bottomColor {
    UIColor *midColor = [UIColor colorWithRed:0.5f green:0.7f blue:1.0f alpha:0.7f];
    CGSize size = CGSizeMake(100, 100);
    UIGraphicsBeginImageContext(size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, startColor.CGColor);
    CGContextAddRect(context, CGRectMake(0, 0, size.width, size.height));
    CGContextFillPath(context);

    CGContextSaveGState(context);
    CGContextTranslateCTM(context, 0, -size.height / 2.0);
    CGContextScaleCTM(1, 1);
    CGContextSetFillColorWithColor(context, midColor.CGColor);
    CGContextAddArc(context, CGPointZero, size.width/2.0, true, 0, 3.14);
    CGContextFillPath(context);

    CGContextRestoreGState(context);
    CGContextSetFillColorWithColor(context, topColor.CGColor);
    CGContextAddRect(context, CGRectMake(0, -size.height / 2.0, size.width, size.height));
    CGContextFillPath(context);

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;
}

Conclusion

In this article, we explored the process of customizing table view cells and removing a gradient when the cell is selected. We covered two approaches: drawing the gradient directly using CGGradient and CGContextDrawLinearGradient, and using a UIImageView with a pre-generated gradient image.

By choosing the most suitable approach for your specific use case, you can achieve a professional-looking table view with customizable gradients.

Last modified on 2023-07-23