html - 为什么当我尝试将 WebView 保存为 PDF 时 NSPrintOperation 创建一个空 PDF？

Question

我正在尝试将 HTML 转换为 OS X 上的 PDF 文件。经过大量挖掘，我发现最好的方法是使用 NSPrintOperation。这是我用来将 HTML 字符串转换为 PDF 的代码:

WebView *webview = [[WebView alloc] init];
[webview.mainFrame loadHTMLString:htmlString baseURL:nil];

NSDictionary *printOpts = @{
                            NSPrintJobDisposition: NSPrintSaveJob,
                            NSPrintSavePath: outputFilePath
                            };
NSPrintInfo *printInfo = [[NSPrintInfo alloc] initWithDictionary:printOpts];
printInfo.horizontalPagination = NSAutoPagination;
printInfo.verticalPagination = NSAutoPagination;
NSPrintOperation *printOp = [NSPrintOperation 
                             printOperationWithView:webview.mainFrame.frameView.documentView
                                          printInfo:printInfo];
printOp.showsPrintPanel = NO;
printOp.showsProgressPanel = NO;

[printOp runOperation];

此代码确实生成了 PDF 文件，但 PDF 文件是空的。是因为 WebView 没有框架吗？我试过使用 dataWithPDFInsideRect:，但这也不起作用。

我应该用 A4 纸大小的框架初始化 webview 吗？或者是其他地方的问题？

Answer 1

我知道这是一个旧话题，但我想发布我今天想出的解决方案。由于 WebView 是异步加载的，关键是设置一个框架加载委托(delegate)回调，然后通过运行循环运行，直到框架加载完成。

我下面的代码创建了一个新的 WebView，然后将 HTML 文件加载到其中:

// Clear the loaded flag
_webViewIsLoaded = NO;

// Fetch the default paper size and init print settings
NSPrintInfo * sharedInfo = [NSPrintInfo sharedPrintInfo];
NSMutableDictionary * sharedDict = [sharedInfo dictionary];
NSMutableDictionary * printInfoDict = [NSMutableDictionary dictionaryWithDictionary:sharedDict];
NSRect printRect = NSZeroRect;
printRect.size = [sharedInfo paperSize];

// Create a new web view
WebView * printView = [[WebView alloc] initWithFrame:printRect];
[printView setFrameLoadDelegate:self];

// Configure the WebView
WebPreferences * preferences = [[WebPreferences alloc] initWithIdentifier:@"com.id.here"];
[preferences setShouldPrintBackgrounds:YES];
[preferences setAllowsAnimatedImageLooping:NO];
[preferences setJavaScriptCanOpenWindowsAutomatically:NO];
[preferences setAutosaves:NO];
[preferences setJavaEnabled:NO];
[preferences setJavaScriptEnabled:NO];
[preferences setCacheModel:WebCacheModelDocumentViewer];        // most memory-efficient setting
[preferences setPlugInsEnabled:NO];                             // disable plugins
[printView setPreferences:preferences];

// Load the HTML file
NSURL * url = [NSURL fileURLWithPath:htmlPath];
NSURLRequest * request = [NSURLRequest requestWithURL:url];
[[printView mainFrame] loadRequest:request];

[printInfoDict setObject:NSPrintSaveJob
                  forKey:NSPrintJobDisposition];
[printInfoDict setObject:saveUrl forKey:NSPrintJobSavingURL];

NSPrintInfo * printInfo = [[NSPrintInfo alloc] initWithDictionary:printInfoDict];
[printInfo setHorizontalPagination:NSFitPagination];
[printInfo setVerticalPagination:NSAutoPagination];
[printInfo setVerticallyCentered:NO];
[printInfo setHorizontallyCentered:YES];

// Wait for the frame to finish loading
while(!_webViewIsLoaded)
{
    @autoreleasepool
    {
        [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.005]];
    }
}

NSPrintOperation * printOp = [NSPrintOperation printOperationWithView:[[[printView mainFrame] frameView] documentView]
                                                            printInfo:printInfo];
[printOp setShowsProgressPanel:YES];
[printOp setShowsPrintPanel:NO];
[printOp runOperation];

接下来，我的框架加载委托(delegate)方法会在框架完全加载后设置一个标志，并调整框架的高度以匹配内容的高度:

-(void)webView:(WebView *)sender didFinishLoadForFrame:(WebFrame *)webFrame
{
    _webViewIsLoaded = YES;

    NSRect webFrameRect = [[[webFrame frameView] documentView] frame];
    NSRect webViewRect = [webView frame];

    // Resize the webview so it fits all of its contents
    NSRect newWebViewRect = NSMakeRect(webViewRect.origin.x,
                                   webViewRect.origin.y - (NSHeight(webFrameRect) - NSHeight(webViewRect)),
                                   NSWidth(webViewRect),
                                   NSHeight(webFrameRect));
    [webView setFrame:newWebViewRect];
}

这对于将 HTML 文档保存为 PDF 应该很有效。