objective-c - 如何在iPad的Objective C中解析PDF

我一直坚持解析PDF文件。请指导我如何执行此操作。

头文件。

//PDFViewer.h
@interface PDFViewer : UIView
{
 CGPDFDocumentRef pdf;
}

-(void)drawInContext:(CGContextRef)context;

@end

实现文件

//PDFViewer.m
@implementation PDFViewer


- (id)initWithFrame:(CGRect)frame
{

 if ((self = [super initWithFrame:frame]))
 {
        // Initialization code
  if(self != nil)
  {
   CFURLRef pdfURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), CFSTR("WR1MayJun1S08.pdf"), NULL, NULL);
   pdf = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL);
   CFRelease(pdfURL);
  }
    }
    return self;
}


-(void)drawInContext:(CGContextRef)context
{
 // PDF page drawing expects a Lower-Left coordinate system, so we flip the coordinate system
 // before we start drawing.
 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, kCGPDFCropBox, 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);
}

/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code
}
*/

- (void)dealloc
{
    CGPDFDocumentRelease(pdf);
 [super dealloc];
}


@end

现在，我将此类(PDFViewer.h)添加到我的MainViewController中。

//MainViewController.m

CGRect frame = CGRectMake(0, 200, 300, 500);

PDFViewer *pdfViewer = [[PDFViewer alloc] initWithFrame:frame];
CGContextRef context = UIGraphicsGetCurrentContext();
[pdfViewer drawInContext:context];
[self.view addSubview:pdfViewer];

它什么也没显示。我收到以下错误/警告:

local MultiView[2850] <Error>: CGContextTranslateCTM: invalid context
local MultiView[2850] <Error>: CGContextScaleCTM: invalid context
local MultiView[2850] <Error>: CGContextSaveGState: invalid context
local MultiView[2850] <Error>: CGContextConcatCTM: invalid context
local MultiView[2850] <Error>: CGContextRestoreGState: invalid context

我想念什么？

问候。

最佳答案

显然，如果没有，UIGraphicsGetCurrentContext不会返回上下文。

您尝试在 View 初始化时获取上下文，那时没有可用的上下文。在调用-[UIView drawRect:]之前，将有效上下文压入堆栈。这应该工作:

//PDFViewer.m
@implementation PDFViewer

- (void)drawRect:(CGRect)rect {
    [self drawInContext:UIGraphicsGetCurrentContext()];
}

@end

编辑
尽管我不喜欢给任何人复制并粘贴的代码，但如果您不了解我的最新评论，我认为还没有其他选择。我不知道您尝试了什么，但是如果您想了解我的意思，这是您唯一能想到的:

//PDFViewer.m
@implementation PDFViewer

- (id)initWithFrame:(CGRect)frame
{

    if (self = [super initWithFrame:frame])
    {
        CFURLRef pdfURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), CFSTR("WR1MayJun1S08.pdf"), NULL, NULL);
        pdf = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL);
        CFRelease(pdfURL);
    }
    return self;
}

-(void)drawInContext:(CGContextRef)context
{
    // PDF page drawing expects a Lower-Left coordinate system, so we flip the coordinate system
    // before we start drawing.
    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, kCGPDFCropBox, 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);
}

- (void)drawRect:(CGRect)rect {
    [self drawInContext:UIGraphicsGetCurrentContext()];
}

- (void)dealloc
{
    CGPDFDocumentRelease(pdf);
    [super dealloc];
}

@end

-

//MainViewController.m

CGRect frame = CGRectMake(0, 200, 300, 500);

PDFViewer *pdfViewer = [[PDFViewer alloc] initWithFrame:frame];
[self.view addSubview:pdfViewer];