ios 导航渐变

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#define NAVBAR_COLORCHANGE_POINT (IMAGE_HEIGHT - NAV_HEIGHT*2)
#define IMAGE_HEIGHT 280
#define NAV_HEIGHT 64





#pragma mark  导航渐变

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGFloat offsetY = scrollView.contentOffset.y;
    if (offsetY > NAVBAR_COLORCHANGE_POINT)
    {
        [self changeNavBarAnimateWithIsClear:NO];
        self.title = @"视频";
    }
    else
    {
        [self changeNavBarAnimateWithIsClear:YES];
        self.title = @"";
    }
}

- (void)changeNavBarAnimateWithIsClear:(BOOL)isClear
{
    __weak typeof(self) weakSelf = self;
    [UIView animateWithDuration:0.6 animations:^
     {
         __strong typeof(self) pThis = weakSelf;
         if (isClear == YES) {
             pThis.navigationController.navigationBar.alpha=0.6;
             [pThis.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"millcolorGrad"] forBarMetrics:UIBarMetricsDefault];
            
             
         } else {
             pThis.navigationController.navigationBar.alpha=1;
             [pThis.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"millcolorGrad"] forBarMetrics:UIBarMetricsDefault];
         }
     }];
}