向後循環通過NSArray

Question

我試圖通過單擊按鈕向後循環數組。

我目前的代碼很接近，但並不完美。

- (void)viewDidLoad { 
self.imageNames = [NSArray arrayWithObjects:@"MyFirstImage", @"AnotherImage", nil]; 
currentImageIndex = 0; 
[super viewDidLoad]; 
} 

...是什麼在起作用：

- (IBAction)change { 
UIImage* imageToShow = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:[imageNames objectAtIndex:currentImageIndex] ofType:@"png"]; 
currentImageIndex++; 
if (currentImageIndex >= imageNames.count) { 
    currentImageIndex = 0; 
} 
} 

...，什麼是不工作：

- (IBAction)changeBack { 
UIImage* imageToShow = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:[imageNames objectAtIndex:currentImageIndex] ofType:@"png"]; 
currentImageIndex--; 
if (currentImageIndex >= imageNames.count) { 
    currentImageIndex = 0; 
} 
} 

任何幫助，很高興地感謝！

謝謝！

Answer 1

您需要先更改索引，然後獲取圖像。當退步需要索引重置爲最大值（計數1）當你去否定：

- (IBAction)changeBack { 
    currentImageIndex--; 
    if (currentImageIndex < 0) { // was first image 
     currentImageIndex = imageNames.count-1; // last image 
    } 

    UIImage* imageToShow = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:[imageNames objectAtIndex:currentImageIndex] ofType:@"png"]; 
} 

向前移動到下一個圖像：

- (IBAction)change { 
    currentImageIndex++; 
    if (currentImageIndex >= imageNames.count) { // was last image 
     currentImageIndex = 0; // back to first image 
    } 

    UIImage* imageToShow = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:[imageNames objectAtIndex:currentImageIndex] ofType:@"png"]; 
} 

Answer 2

也許在changeBack方法，你應該改變這行代碼顯示如下：

if (currentImageIndex <= 0) {
currentImageIndex = imageNames.count;
}

（當用戶獲取過去的第一個圖像這是假設，他們回到過去一個）