Re: Image from WebView is sometimes blank
Re: Image from WebView is sometimes blank
- Subject: Re: Image from WebView is sometimes blank
- From: Duncan Oliver <email@hidden>
- Date: Thu, 20 May 2010 14:20:57 -0500
Thanks. I added the layout line, and that seems to have fixed it. I'll
have to do some more testing, but so far, I haven't had the problem
anymore.
---
Duncan Oliver
email@hidden
On Fri, May 14, 2010 at 1:27 PM, Adam R. Maxwell <email@hidden> wrote:
>
> 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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