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如何使用iOS以编程方式生成PDF的缩略图?

cocoa-touch pdf objective-c ios

Jamie Chapman · 技术社区 · 15 年前

UIWebViews 目前。理想情况下,我希望能够在 UITableView 不加载许多不同的同时。。。他们加载一个文档已经够慢了-别介意10+!

我该怎么做?

UIDocumentInteractionController 或 UIWebView

3 回复 | 直到 6 年前

Jay Bhalani 9 年前

苹果公司在 CoreGraphics 直接绘制PDF内容的级别。据我所知,在 UIKit CGContextDrawPDFPage; 按正常值 核心图形 还有其他方法可以从数据源创建PDF引用,然后从PDF获取页面引用。然后需要处理缩放和转换到所需视图的问题,并警告您需要执行水平翻转,因为PDF(和OS X)使用左下角作为原点,而iOS使用左上角。示例代码,在我的头顶上:

UIGraphicsBeginImageContext(thumbnailSize);
CGPDFDocumentRef pdfRef = CGPDFDocumentCreateWithProvider( (CGDataProviderRef)instanceOfNSDataWithPDFInside );
CGPDFPageRef pageRef = CGPDFDocumentGetPage(pdfRef, 1); // get the first page

CGContextRef contextRef = UIGraphicsGetCurrentContext();

// ignore issues of transforming here; depends on exactly what you want and
// involves a whole bunch of normal CoreGraphics stuff that is nothing to do
// with PDFs
CGContextDrawPDFPage(contextRef, pageRef);

UIImage *imageToReturn = UIGraphicsGetImageFromCurrentImageContext();

// clean up
UIGraphicsEndImageContext();
CGPDFDocumentRelease(pdfRef);

return imageToReturn;

估计你会想用 CGPDFPageGetBoxRect(pageRef, kCGPDFCropBox)

-renderInContext: 方法打开 CALayer (见 QA 1703 )获取屏幕截图的旧方法是 UIGetScreenImage

不管是哪种情况,PDF都不会那么快绘制。您可能需要填充该表,然后在后台线程上绘制缩略图,在可用时将其向上推。您不能在后台线程上安全地使用UIKit对象,但是 核心图形 东西是安全的。

alones 15 年前

NSURL* pdfFileUrl = [NSURL fileURLWithPath:finalPath];
CGPDFDocumentRef pdf = CGPDFDocumentCreateWithURL((CFURLRef)pdfFileUrl);
CGPDFPageRef page;

CGRect aRect = CGRectMake(0, 0, 70, 100); // thumbnail size
UIGraphicsBeginImageContext(aRect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
UIImage* thumbnailImage;


NSUInteger totalNum = CGPDFDocumentGetNumberOfPages(pdf);

for(int i = 0; i < totalNum; i++ ) {


    CGContextSaveGState(context);
    CGContextTranslateCTM(context, 0.0, aRect.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    CGContextSetGrayFillColor(context, 1.0, 1.0);
    CGContextFillRect(context, aRect);


    // Grab the first PDF page
    page = CGPDFDocumentGetPage(pdf, i + 1);
    CGAffineTransform pdfTransform = CGPDFPageGetDrawingTransform(page, kCGPDFMediaBox, aRect, 0, true);
    // And apply the transform.
    CGContextConcatCTM(context, pdfTransform);

    CGContextDrawPDFPage(context, page);

    // Create the new UIImage from the context
    thumbnailImage = UIGraphicsGetImageFromCurrentImageContext();

    //Use thumbnailImage (e.g. drawing, saving it to a file, etc)

    CGContextRestoreGState(context);

}


UIGraphicsEndImageContext();    
CGPDFDocumentRelease(pdf);

Emil 8 年前

下面是生成pdf页面的UIImage缩略图的swift 3方法

static func getThumbnailForPDF(_ urlString:String, pageNumber:Int) -> UIImage? {
    let bundle = Bundle.main
    let path = bundle.path(forResource: urlString, ofType: "pdf")
    let pdfURL = URL(fileURLWithPath: path!)

    let pdf = CGPDFDocument(pdfURL as CFURL )!
    let page = pdf.page(at: pageNumber)!
    let rect = CGRect(x: 0, y: 0, width: 100.0, height: 70.0) //Image size here

    UIGraphicsBeginImageContext(rect.size)
    let context = UIGraphicsGetCurrentContext()!

    context.saveGState()
    context.translateBy(x: 0, y: rect.height)
    context.scaleBy(x: 1.0, y: -1.0)
    context.setFillColor(gray: 1.0, alpha: 1.0)
    context.fill(rect)


    let pdfTransform = page.getDrawingTransform(CGPDFBox.mediaBox, rect: rect, rotate: 0, preserveAspectRatio: true)
    context.concatenate(pdfTransform)
    context.drawPDFPage(page)

    let thumbImage = UIGraphicsGetImageFromCurrentImageContext()
    context.restoreGState()

    UIGraphicsEndImageContext()

    return thumbImage
}