CGPDFDocument缩放

Question

我刚刚开始建立一个应用程序，将显示PDF文档。我一直在实验，继承UIView并使用苹果演示中的代码。我有一个PDF文档，其中包含一个1024x748像素的图像，分辨率为131ppi，因此它应该在横向视图中填充iPad屏幕。

当我运行这个应用程序时，pdf在iPad屏幕上居中缩放到其完整大小的大约.25%。为什么PDF不是全尺寸显示的？

来自我的自定义UIView的代码：

-(id)initWithFrame:(CGRect)frame PDFName:(NSString *)pdfName
{
    self = [super initWithFrame:frame];
    if(self != nil)
    {
        self.backgroundColor = [UIColor blueColor];
        self.opaque = YES;
        self.clearsContextBeforeDrawing = YES;

        CFURLRef pdfURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), (CFStringRef)pdfName, NULL, NULL);
        pdf = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL);
        CFRelease(pdfURL);
    }

    return self;
}


- (void)drawRect:(CGRect)rect {

    // PDF page drawing expects a Lower-Left coordinate system, so we flip the coordinate system
    // before we start drawing.
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, 0.0, self.bounds.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    // Grab the first PDF page
    CGPDFPageRef page = CGPDFDocumentGetPage(pdf, 1);

    // We're about to modify the context CTM to draw the PDF page where we want it, so save the graphics state in case we want to do more drawing
    CGContextSaveGState(context);
    // CGPDFPageGetDrawingTransform provides an easy way to get the transform for a PDF page. It will scale down to fit, including any
    // base rotations necessary to display the PDF page correctly. 
    CGAffineTransform pdfTransform = CGPDFPageGetDrawingTransform(page, kCGPDFMediaBox, self.bounds, 0, true);
    // And apply the transform.
    CGContextConcatCTM(context, pdfTransform);
    // Finally, we draw the page and restore the graphics state for further manipulations!
    CGContextDrawPDFPage(context, page);
    CGContextRestoreGState(context);

}

Answer 1

答案很简单。将PDF中图像的ppi更改为72 ppi (仍为1024 x 748)。现在它正确地填满了屏幕。我认为我需要匹配iPads像素密度，但我猜不是。

Jk