Trasforma lo sfondo di UIView in una sfumatura senza sottoclasse

Question

C'è un modo per rendere lo sfondo di una UIView un gradiente senza sottoclassarlo? Preferirei non usare un file di immagine per farlo. Sembra ottuso dover sottoclassare UIView solo per disegnare un gradiente per lo sfondo.

Answer 1

Puoi usare +[UIColor colorWithPatternImage:] per produrre uno sfondo a motivi. Esempio (porta il tuo CGGradient):

// Allocate color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
// Allocate bitmap context
CGContextRef bitmapContext = CGBitmapContextCreate(NULL, 320, 480, 8, 4 * 320, colorSpace, kCGImageAlphaNoneSkipFirst);
//allocate myGradient
CGFloat locationList[]  = {0.0f, 1.0f};
CGFloat colorList[]     = {0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f};
CGGradientRef myGradient   = CGGradientCreateWithColorComponents(colorSpace, colorList, locationList, 2);
// Draw Gradient Here
CGContextDrawLinearGradient(bitmapContext, myGradient, CGPointMake(0.0f, 0.0f), CGPointMake(320.0f, 480.0f), 0);
// Create a CGImage from context
CGImageRef cgImage = CGBitmapContextCreateImage(bitmapContext);
// Create a UIImage from CGImage
UIImage *uiImage = [UIImage imageWithCGImage:cgImage];
// Release the CGImage
CGImageRelease(cgImage);
// Release the bitmap context
CGContextRelease(bitmapContext);
// Release the color space
CGColorSpaceRelease(colorSpace);
// Create the patterned UIColor and set as background color
[targetView setBackgroundColor:[UIColor colorWithPatternImage:image]];

Probabilmente sarà comunque più semplice creare una sottoclasse UIView. Utilizzerà anche meno memoria.

Answer 2

Potresti fare:

Swift > = 4.0:

let gradient = CAGradientLayer()
gradient.frame = view.bounds
gradient.colors = [UIColor.red.cgColor, UIColor.white.cgColor]
view.layer.insertSublayer(gradient, at: 0)

Swift 3.0:

let gradient = CAGradientLayer()
gradient.frame = view.bounds
gradient.colors = [UIColor.red().cgColor, UIColor.white().cgColor]
view.layer.insertSublayer(gradient, at: 0)

Swift < = 2.3:

let gradient = CAGradientLayer()
gradient.frame = view.bounds
gradient.colors = [UIColor.redColor().CGColor, UIColor.whiteColor().CGColor]
view.layer.insertSublayer(gradient, atIndex: 0)

Objective-C:

CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = self.view.bounds;
gradient.colors = [NSArray arrayWithObjects:(id)[[UIColor redColor] CGColor], (id)[[UIColor whiteColor] CGColor], nil];
[self.view.layer insertSublayer:gradient atIndex:0];

Assicurati di aggiungere anche il framework QuartzCore al tuo progetto (almeno per Objective-C) ...

#import <QuartzCore/QuartzCore.h>

Answer 3

Sono d'accordo con rpetrich, sarebbe più pulito fare solo la sottoclasse UIView. Per un esempio di come eseguire questa operazione, vedere la mia risposta in questo domanda . Se lo si desidera, è possibile creare una sottoclasse UIView con gradiente generico e posizionarla semplicemente dietro le viste con sfondo sfumato.

Answer 4

Cambio la risposta adottata alla mia edizione

+(void) setBlackGradientToView:(UIView*)targetView
{
    CGRect frame = targetView.frame;
    // Allocate color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    //allocate myGradient
    CGFloat locationList[]  = {0.0f, 1.0f};
    CGFloat colorList[]     = {0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f};
    CGGradientRef myGradient   = CGGradientCreateWithColorComponents(colorSpace, colorList, locationList, 2);
    // Allocate bitmap context
    CGContextRef bitmapContext = CGBitmapContextCreate(NULL, frame.size.width, frame.size.height, 8, 4 * frame.size.width, colorSpace, kCGImageAlphaPremultipliedLast);
    //Draw Gradient Here
    CGContextDrawLinearGradient(bitmapContext, myGradient, CGPointMake(0.0f, 0.0f), CGPointMake(0, frame.size.height), 0);
    // Create a CGImage from context
    CGImageRef cgImage = CGBitmapContextCreateImage(bitmapContext);
    // Create a UIImage from CGImage
    UIImage *uiImage = [UIImage imageWithCGImage:cgImage];
    // Release the CGImage
    CGImageRelease(cgImage);
    // Release the bitmap context
    CGContextRelease(bitmapContext);
    // Release the color space
    CGColorSpaceRelease(colorSpace);

    //Create the patterned UIColor and set as background color
    [targetView setBackgroundColor:[UIColor colorWithPatternImage:uiImage]];
    //return uiImage;
}