以上是博主寫的漸變導航欄的進化之路，上一篇部落格最後說明了升級版中的bug，在這一版中對這一bug進行了修復，其實很簡單，就是增加了一個新的變數來給一個全域性的透明度，在上下滾動時改變這個全域性的透明度，然後判斷透明度的邊界，下面來看看程式碼吧：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.view.backgroundColor=[UIColor whiteColor];

    lhAlpha = 1
 
;
}
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{


    currentPostion = scrollView.contentOffset.y;

    if (currentPostion > 0) {
        if (currentPostion - _lastPosition >= 0) {
            if ([[NSUserDefaults standardUserDefaults]objectForKey:@"first"]!=nil) {
                [[NSUserDefaults
 
 standardUserDefaults]removeObjectForKey:@"first"];
                [[NSUserDefaults standardUserDefaults]synchronize];
//                [NSObject cancelPreviousPerformRequestsWithTarget:self];
//                [self performSelector:@selector(scrollViewDidEndScrollingAnimation:) withObject:nil afterDelay:0.00001];
 

                [[NSUserDefaults standardUserDefaults]setObject:@"1" forKey:@"second"];
                [[NSUserDefaults standardUserDefaults]synchronize];
                stopPosition = currentPostion + 64;

            }


            _lastPosition = currentPostion;
            NSLog(@"ScrollUp now    current:%f    last:%f    stop:%f",currentPostion,_lastPosition,stopPosition);
            if (lhAlpha >= 0) {
                lhAlpha = lhAlpha - 0.025f;
            }
            else
            {
                lhAlpha = 0;
            }
            self.navigationController.navigationBar.alpha = lhAlpha;

//            self.navigationController.navigationBar.alpha = 1 - currentPostion / 400;


        }
        else
        {
            if ([[NSUserDefaults standardUserDefaults]objectForKey:@"second"]!=nil) {
                [[NSUserDefaults standardUserDefaults]removeObjectForKey:@"second"];
                [[NSUserDefaults standardUserDefaults]synchronize];
//                [NSObject cancelPreviousPerformRequestsWithTarget:self];
//                [self performSelector:@selector(scrollViewDidEndScrollingAnimation:) withObject:nil afterDelay:0.00001];
                [[NSUserDefaults standardUserDefaults]setObject:@"1" forKey:@"first"];
                [[NSUserDefaults standardUserDefaults]synchronize];
                stopPosition = currentPostion + 64;

            }
            _lastPosition = currentPostion;
            NSLog(@"ScrollDown now    current:%f   last:%f    stop:%f",currentPostion,_lastPosition,stopPosition);
            if (lhAlpha <= 1) {
                //這裡的0.025自己可以調整，有的上下滾動透明度變化一個快一個慢，切記不要讓向下的小於向上的，否則滾動到頂端導航欄是透明的
                lhAlpha = lhAlpha + 0.025f;
            }
            else
            {
                lhAlpha = 1;
            }
            self.navigationController.navigationBar.alpha = lhAlpha;
            //            self.navigationController.navigationBar.alpha = (stopPosition - currentPostion)/200;
        }

    }

}

Demo的下載地址：下載地址

建議先看一下前面兩篇，這樣會增加理解，實現不難，主要是一個思路。