Ios 如何确定 WKWebView 的内容大小

在iOS 8及更高版本下运行时，我正在try 将动态分配的UIWebView实例替换为WKWebView实例，但我找不到确定WKWebView内容大小的方法.

我的Web视图嵌入在一个更大的UIScrollView容器中，因此我需要确定Web视图的理想大小.这将允许我修改其框架以显示其所有HTML内容，而无需在Web视图中滚动，并且我将能够为滚动视图容器设置正确的高度(通过设置scroll view.contentSize).

我试过sizeToFit和sizeThatFits，但没有成功.下面是创建WKWebView实例并将其添加到容器滚动视图的代码:

// self.view is a UIScrollView sized to something like 320.0 x 400.0.
CGRect wvFrame = CGRectMake(0, 0, self.view.frame.size.width, 100.0);
self.mWebView = [[[WKWebView alloc] initWithFrame:wvFrame] autorelease];
self.mWebView.navigationDelegate = self;
self.mWebView.scrollView.bounces = NO;
self.mWebView.scrollView.scrollEnabled = NO;

NSString *s = ... // Load s from a Core Data field.
[self.mWebView loadHTMLString:s baseURL:nil];

[self.view addSubview:self.mWebView];

下面是一个实验性的didFinishNavision方法:

- (void)webView:(WKWebView *)aWebView
                             didFinishNavigation:(WKNavigation *)aNavigation
{
    CGRect wvFrame = aWebView.frame;
    NSLog(@"original wvFrame: %@\n", NSStringFromCGRect(wvFrame));
    [aWebView sizeToFit];
    NSLog(@"wvFrame after sizeToFit: %@\n", NSStringFromCGRect(wvFrame));
    wvFrame.size.height = 1.0;
    aWebView.frame = wvFrame;
    CGSize sz = [aWebView sizeThatFits:CGSizeZero];
    NSLog(@"sizeThatFits A: %@\n", NSStringFromCGSize(sz));
    sz = CGSizeMake(wvFrame.size.width, 0.0);
    sz = [aWebView sizeThatFits:sz];
    NSLog(@"sizeThatFits B: %@\n", NSStringFromCGSize(sz));
}

下面是生成的输出:

2014-12-16 17:29:38.055 App[...] original wvFrame: {{0, 0}, {320, 100}}
2014-12-16 17:29:38.055 App[...] wvFrame after sizeToFit: {{0, 0}, {320, 100}}
2014-12-16 17:29:38.056 App[...] wvFrame after sizeThatFits A: {320, 1}
2014-12-16 17:29:38.056 App[...] wvFrame after sizeThatFits B: {320, 1}

sizeToFit调用没有效果，sizeThatFits始终返回高度1.