iOS-更改UIButton或自定义UIButton的渐变背景

debugcn 发表于 Dev

里博尔·扎普勒塔尔（Libor Zapletal）

我用.h文件创建了自己的派生自UIButton的类：

@interface MenuButton : UIButton

- (void)changeBackground;

@end

在实现中，我尝试添加一些方法来更改背景，但到目前为止没有成功：

#import "MenuButton.h"
#import "GradientLayers.h"

@implementation MenuButton

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self commonInit];
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)aDecoder;
{
    self = [super initWithCoder:aDecoder];
    if (self) {
        [self commonInit];
    }
    return self;
}

- (void)commonInit;
{

    // Gradient background
    CAGradientLayer *gradient = [GradientLayers darkBlueBackground];
    gradient.frame = [self layer].bounds;

    // Insert background
    [[self layer] insertSublayer:gradient atIndex:0];

    [[self layer] setCornerRadius:10.0f];
    [[self layer] setMasksToBounds:YES];
    [[self layer] setBorderWidth:2];
    [[self layer] setBorderColor:[[UIColor blackColor] CGColor]];

}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    // handle touch
    [super touchesEnded:touches withEvent:event];

    if ([self state] != UIControlStateSelected)
    {
        CAGradientLayer *gradient = [GradientLayers blackBackground];
        gradient.frame = [self layer].bounds;
        [[self layer] insertSublayer:gradient atIndex:0];
    }
    else
    {
        CAGradientLayer *gradient = [GradientLayers darkBlueBackground];
        gradient.frame = [self layer].bounds;
        [[self layer] insertSublayer:gradient atIndex:0];
    }
}

- (void)changeBackground
{
    CAGradientLayer *gradient = [[[self layer] sublayers] firstObject];
    gradient = [GradientLayers blackBackground];
    [[self layer] insertSublayer:gradient atIndex:0];
    [self setNeedsDisplay];
}

@end

GradientLayer.m文件的一部分：

#import "GradientLayers.h"

@implementation GradientLayers

+ (CAGradientLayer*) blackBackground {
    // similar to darkBlueBackground
}

+ (CAGradientLayer*) darkBlueBackground {
    // Create colors
    UIColor *darkOp = [UIColor colorWithRed:0.039f green:0.106f blue:0.278f alpha:1.0];
    UIColor *lightOp = [UIColor colorWithRed:0.133f green:0.267f blue:0.65f alpha:1.0];

    // Create gradient
    CAGradientLayer *gradient = [CAGradientLayer layer];

    // Set colors
    gradient.colors = [NSArray arrayWithObjects:
                       (id)lightOp.CGColor,
                       (id)darkOp.CGColor,
                       nil];

    // Shadow
    gradient.shadowOffset = CGSizeMake(3.0f, 3.0f);
    gradient.shadowColor = [UIColor blackColor].CGColor;
    gradient.shadowOpacity = 0.6;
    gradient.shadowRadius = 10;

    // Other options
    gradient.borderWidth = 0.5f;
    gradient.borderColor = [UIColor colorWithRed:0.0f green:0.0f blue:0.0f alpha:1.0].CGColor;
    gradient.cornerRadius = 10;

    return gradient;
}

@end

我在commonInit中设置了带有darkBlueBackground的按钮。这算不上问题。但是我想在用户点击按钮后更改它，到目前为止没有运气。如果设置断点，则处于touchesEnded或changeBackground，但是执行后，按钮的背景与以前相同。那么如何将背景更改为其他渐变背景呢？谢谢

尼尔

因为该[self layer].sublayers数组是按从后到前的顺序列出的（https://developer.apple.com/library/mac/documentation/graphicsimaging/reference/CALayer_class/Introduction/Introduction.html#//apple_ref/occ/instp/CALayer/sublayers），通过将替换层插入index 0，您总是将其放在旧的渐变后面。

您应该删除旧的渐变图层，然后添加新的渐变图层。

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    // handle touch
    [super touchesEnded:touches withEvent:event];

    // Remove old gradient here
    [[[[self layer] sublayers] objectAtIndex:0] removeFromSuperlayer];

    if ([self state] != UIControlStateSelected)
    {
        CAGradientLayer *gradient = [GradientLayers blackBackground];
        gradient.frame = [self layer].bounds;
        [[self layer] insertSublayer:gradient atIndex:0];
    }
    else
    {
        CAGradientLayer *gradient = [GradientLayers darkBlueBackground];
        gradient.frame = [self layer].bounds;
        [[self layer] insertSublayer:gradient atIndex:0];
    }
}

- (void)changeBackground
{
    // Remove old gradient here
    [[[[self layer] sublayers] objectAtIndex:0] removeFromSuperlayer];

    CAGradientLayer *gradient = [[[self layer] sublayers] firstObject];
    gradient = [GradientLayers blackBackground];
    [[self layer] insertSublayer:gradient atIndex:0];
    [self setNeedsDisplay];
}

您确实应该更好地跟踪渐变，因此您不必不断地用相同的渐变删除和替换它。也许只是显示和隐藏所选状态，而该状态始终位于未突出显示的版本上方。

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