On May 11, 2010, at 2:33 PM, Duncan Oliver wrote: > I have a WebView that I use to capture a thumbnail of a loaded webpage > using cacheDisplayInRect:. The WebView object is created > programmatically and not attached to a window. About half the time, > the image it grabs is blank. I can't seem to figure out if I'm trying > to grab it too soon or what. Would love to know how to get a completed > image all the time. Thanks in advance.
This can be kind of tricky, especially when you need to make it work for
arbitrary pages; just figuring out when the webview finishes loading is tricky,
since -[WebView isLoading] doesn't account for redirection.
>
> Here's the code:
>
> - (void)webView:(WebView *)sender didFinishLoadForFrame:(WebFrame *)frame
> {
> if ([frame isEqualTo:[sender mainFrame]])
> {
My first guess is that pages aren't fully loaded when you get this callback,
but that's generally only a problem with redirects.
> if ([sender saveThumbnail] == YES)
> {
> NSView *mainFrameView = sender.mainFrame.frameView;
> NSBitmapImageRep *thumbnailImageRep = [mainFrameView
> bitmapImageRepForCachingDisplayInRect:[mainFrameView frame]];
> [sender cacheDisplayInRect:[mainFrameView frame]
> toBitmapImageRep:thumbnailImageRep];
Another potential problem is that you need to force layout in the
WebDocumentView; this shouldn't be necessary, but I couldn't find any other
workaround. Try sending
[[mainFrameView documentView] layout];
before calling -cacheDisplayInRect:toBitmapImageRep:. This fixed a bunch of
random white page issues for me. If you use -[WebFrameView
setAllowsScrolling:NO] at some point, the problem is much worse (as of Safari
4.0.3).
I have a BSD-licensed web thumbnail class here:
http://code.google.com/p/fileview/source/browse/trunk/fileview/FVWebViewIcon.m
It's complicated by threading issues, but shows one way to track redirected
frames during loading, and also how to draw.
hth,
Adam
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