如何更改图像透明度实时在IOS

Question

我在IOS初学者，我想通过旋转iPhone来改变图像的不透明度并实时显示在视图中它

#import "ViewController.h" 

@interface ViewController() 

@end 

@implementation ViewController 


- (void)viewDidLoad { 
[super viewDidLoad]; 
// Do any additional setup after loading the view, typically from a nib. 
self.motionManager = [[CMMotionManager alloc]init]; 
self.motionManager.accelerometerUpdateInterval = 0.1; 
if([self.motionManager isAccelerometerAvailable]){ 

    [self.motionManager startAccelerometerUpdatesToQueue:[NSOperationQueue mainQueue] withHandler:^(CMAccelerometerData *accelerometerData, NSError *error){ 
     if(error){ 
      [self.motionManager stopAccelerometerUpdates]; 
     }else{ 

      accX = floor(accelerometerData.acceleration.x * 100)/100; 
      accY = floor(accelerometerData.acceleration.y * 100)/100; 
      accZ = floor(accelerometerData.acceleration.z * 100)/100; 
      NSLog(@"x = %f", accX); 
      NSLog(@"y = %f", accY); 
      NSLog(@"z = %f", accZ); 

     } 
    }]; 
}else{ 
    NSLog(@"Gyroscope is not available."); 
} 
NSBundle *bundle = [NSBundle mainBundle]; 
self.solder = [[UIImage alloc]initWithContentsOfFile:[bundle  
pathForResource:@"solder" ofType:@"jpg"]]; 
self.woman= [[UIImage alloc]initWithContentsOfFile:[bundle 
pathForResource:@"woman" ofType:@"jpg"]]; 

    self.solderImage.alpha = accX; 

    self.solderImage.image = self.solder; 


} 


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

@end 

我从iphone获得了加速度计值，并使用它来更改图像的不透明度，但无法实时显示结果，我该如何操作？

Answer 1

问题是在后台线程上调用startAccelerometerUpdatesToQueue:withHandler的处理程序块，并禁止在后台线程上进行UI更改，并且会导致未定义的行为。

一个解决方案是更新调度块内的阿尔法：

accX = floor(accelerometerData.acceleration.x * 100)/100; 
accY = floor(accelerometerData.acceleration.y * 100)/100; 
accZ = floor(accelerometerData.acceleration.z * 100)/100; 

dispatch_async(dispatch_get_main_queue(), ^{ 
    self.solderImage.alpha = accX; 
}); 

甲调度块增加了块内的指令，以在主线程队列中。这样，它将在主线程上运行，任何UI更改都能正常工作。