iOS 自动缩放到一定比例，视图还在中间显示

先布局完 - 延时方法，设置缩放比例；

CGRect bgFrame = self.bgView.frame;
bgFrame.size = CGSizeMake(2*maxRadiusOfX,2*maxRadiusOfY+300);
self.bgView.frame = bgFrame;
self.mainScrollView.contentSize = CGSizeMake(2*maxRadiusOfX,2*maxRadiusOfY+300);
[self.mainScrollView setContentOffset:CGPointMake((self.mainScrollView.contentSize.width-kScreenWidth)/2,(self.mainScrollView.contentSize.height-self.view.height)/2) animated:YES];
[self drawKnowledgeTree:self.parentItem.layerReq withCenterPoint:CGPointMake(maxRadiusOfX, (maxRadiusOfY+150)) startAngle:0 radius:60 isShow:YES];

[self performSelector:@selector(delaySetZoomScale) withObject:nil afterDelay:0.5];

``
-(void)delaySetZoomScale{
[self.mainScrollView setZoomScale:0.3 animated:YES];
}

``

缩放完，代理回调设置视图在中心位置；

``

pragma mark - UIScrollViewDelegate

• (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView{
  NSLog(@"开始缩放");
  return self.bgView;
  }

• (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale {

  if (!self.isFirstScale) {
  self.isFirstScale = YES;
  [self.mainScrollView setContentOffset:CGPointMake((self.mainScrollView.contentSize.width-kScreenWidth)/2,(self.mainScrollView.contentSize.height-self.view.height)/2) animated:YES];
  }

}

``