Kevin Kevin - 1 year ago 1003
iOS Question

Disable magnification gesture in WKWebView

I'm looking for a way to disable the "pinch to zoom" magnification gesture on the iOS implementation of WKWebView. There is a magnification BOOL property available for OS X but it doesn't seem to be available on iOS.


/* @abstract A Boolean value indicating whether magnify gestures will
change the web view's magnification.
@discussion It is possible to set the magnification property even if
allowsMagnification is set to NO.
The default value is NO.
@property (nonatomic) BOOL allowsMagnification;

I've, also, tried look at the WKWebView's gesture recognizers but that seems to be turning up an empty array. I'm assuming the actual recognizers are bured deeper in the component's structure (fairly complex, by the looks of it) and would rather not go digging for them if at all possible.

I know of possible hacks that could potentially disable the gesture from firing (selectively passing gestures to the WebView, add child view to capture pinch gesture, etc) but I've always found those introduce lag into the event and want to keep the implementation as clean/hack free as possible.

Answer Source

WKWebView seems to respect the viewport meta tag the same way Mobile Safari does (as to be expected). So, I found injecting that tag into the DOM through javascript after a page load does the trick. I would be weary of this solution unless you know exactly what HTML is being loaded into the webview, otherwise I suspect it would have unintended consequences. In my case, I'm loading HTML strings, so I can just add it to the HTML I ship with the app.

To do it generically for any webpage:

- (void)webView:(WKWebView *)webView didCommitNavigation:(WKNavigation *)navigation {
    NSString *javascript = @"var meta = document.createElement('meta');meta.setAttribute('name', 'viewport');meta.setAttribute('content', 'width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no');document.getElementsByTagName('head')[0].appendChild(meta);";

    [webView evaluateJavaScript:javascript completionHandler:nil];

It might be wise to take a look at what kind of navigation has just been completed, since only a new page will need this javascript executed.

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