以编程方式更改UIImage的Alpha

Question

我仍在探索xCode / Objective-C，而且我想知道如何更改UIImage的alpha。 我尝试编写自己的代码，但在类型UIImage的对象上收到错误“属性'alpha'”。 如果我注释掉Alpha更改线，则初始屏幕将起作用。 我的代码如下。

//
//  ViewController.m

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic,weak) IBOutlet UIImage *logo;

@end

@implementation ViewController

ADBannerView *_bannerView;
- (void)viewDidLoad
{
    [super viewDidLoad];
    [self.view addSubview:_bannerView];

    [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(showLogo:) userInfo:nil repeats:NO];

}

- (void)showLogo:(NSTimer *) timer{
    [UIView animateWithDuration:2.0 animations:^{
    self.logo.alpha = 1.0;
} completion:^(BOOL finished){

    [UIView animateWithDuration:2.0 animations:^{
        self.logo.alpha = 0.0;
    } completion:^(BOOL finished){
        ViewController *controller  = [self.storyboard instantiateViewControllerWithIdentifier:@"Menu"];
        [self.navigationController pushViewController:controller animated:YES];
    }];

}];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

//谢谢！

Answer 1

您需要更改包含在其中的UIImageView alpha， UIImage没有alpha属性。

Answer 2

最好的方法由@JMarsh显示

我找到了更改Alpha值的方法。 你可以试试看

imageView.image=[self imageByApplyingAlpha:image]

//更改图片的Alpha

   - (UIImage *)imageByApplyingAlpha:(CGFloat) alpha {
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0f);

    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGRect area = CGRectMake(0, 0, self.size.width, self.size.height);

    CGContextScaleCTM(ctx, 1, -1);
    CGContextTranslateCTM(ctx, 0, -area.size.height);

    CGContextSetBlendMode(ctx, kCGBlendModeMultiply);

    CGContextSetAlpha(ctx, alpha);

    CGContextDrawImage(ctx, area, self.CGImage);

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return newImage;
}