UIWebPaginationModeTopToBottom causes UIWebView to be fully opaque

Originator:cspickert
Number:rdar://15300937 Date Originated:23-Oct-2013 02:59 PM
Status:Open Resolved:
Product:iOS SDK Product Version:7.0
Classification:Other Bug Reproducible:Always
 
Summary:

When a UIWebView instance's `paginationMode` is set to `UIWebPaginationModeUnpaginated`, it is possible to make the web view completely transparent if the document loaded is also transparent. When the web view's `paginationMode` is set to `UIWebPaginationModeTopToBottom`, it is not possible to make the web view fully transparent.

Steps to Reproduce:

1. Instantiate a UIWebView instance and set its `opaque` property to `NO`, its `backgroundColor` to `[UIColor clearColor]`, and its `paginationMode` to `UIWebPaginationModeTopToBottom`.

2. Load the following HTML document into the web view, e.g. using `-[UIWebView loadHTMLString:baseURL:]`:

    <!DOCTYPE html>
    <html>
        <head>
            <style type="text/css">
                body, html {
                    background-color:transparent !important;
                }
                h1 {
                    color: black;
                }
            </style>
        </head>
        <body>
            <h1>Testing</h1>
        </body>
    </html>

Note that the `background-color` of the `html` and `body` elements must be set to `transparent`.

3. Set the background color of the web view's superview to something other than white, e.g. `[UIColor blueColor]`.

Expected Results:

If the web view is not opaque and its background color is clear, it should be fully transparent and you should see “Testing” in black on a blue background.

Actual Results:

The web view's background color defaults to opaque white when using the new pagination API introduced in the iOS 7 SDK.

Regression:

This bug was introduced with the iOS 7.0 SDK.

Notes:

Changing the pagination mode of the web view back to `UIWebPaginationModeUnpaginated` yields the expected visual appearance.

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