Programmatically zoom a UIWebView by addressing its UIScrollView

Question

in my xib-based view I have a UIWebView that I need to zoom programmatically.

Since the UIWebView has no own zooming methods I found Max's post that suggested to get the UIWebViews UIScrollView and send the zoom levels to that one.

In my view controller's viewDidLoad method I therefore determined the UIScrollView as follows:

- (void)viewDidLoad {
   // set iVars (both are IBOutlets)
   iWebView.delegate = self;
   iScrollView = [[iWebView subviews] objectAtIndex:0];

   iScrollview.minimumZoomScale = 0.2;
   iScrollview.maximumZoomScale = 4.0;
   iScrollview.zoomScale = iScrollview.minimumZoomScale;

NSLog(@"webViewDidFinishLoad: Current %.3f, Min %.3f, Max %.3f", 
          iMapScrollView.zoomScale, iMapScrollView.minimumZoomScale, iMapScrollView.maximumZoomScale);
   ...
}

The UIWebView (by default) contains a 1000x2000px png-file. The NSLog shows

webViewDidFinishLoad: Current 0.200, Min 0.200, Max 4.000

Trouble comes when I try to update the iScrollView.zoomLevel to a new zoom-factor (lets say to 2.4):

- (void)setPositionWithZoom:(float)xPos down:(float)yPos zoomScale:(float)mZoomScale {
   iScrollView.zoomScale = mZoomScale;
   NSLog(@"setPositionWithZoom: mZoomScale %.3f Current %.3f, Min %.3f, Max %.3f", 
           mZoomScale , iMapScrollView.zoomScale, iMapScrollView.minimumZoomScale, iMapScrollView.maximumZoomScale);
   ...
}

The NSLog shows:

setPositionWithZoom: mZoomScale 2.400 mCurrent 1.000 Min 1.000 Max 1.000

So the zoom-level resets to 1 since the min/max zoomlevels have mysteriously fallen back to that value.

I'm flabbergasted, any clues?

---

EDIT: Further investigation brought me to a touch method that I call from a UIWindow-subclass to forward touch events (implementation of Mithins recipe for grasping touch events with UIWebViews).

It is when this method ( myWebViewTouchesEnded ) in my viewController gets called that the values are wiped out. I have no idea why.

PATCH: I applied a simple patch to define 2 iVars that i use to set the min/max zoomScales back to my custom values within myWebViewTouchesEnded and evrything works ...

Answer 1

Did you mean iScrollView instead of iMapScrollView in you NSLog statement?

Be aware that UIWebView does flakey things with zoomScale, minimumZoomScale and maximumZoomScale.

For example:

When loading a file with scalesPageToFit: if file is a PDF, min... = 1 max... = 32 and zoomScale =1, When you zoom, zoomScale changes appropriately and min... and max... remain unchanged.

if the file is an Excel file, min...=1 max... = some number N and zoomScale =1 When you zoom, zoomScale remains = 1, while max... and min... change, eg set zoomScale =2 and zoomScale will = 1, min... will = 1/2 and max... will = N/2

EDIT: This problem with Excel files applies only when you have zoomed with a pinch gesture.

Answer 2

Try this:

for (UIScrollView *scroll in [myPDFView subviews])
{   
    //Set the zoom level.

    [scroll setZoomScale:2.5f animated:YES];
}