ios - 在 Objective-C 中从 PDF 中提取可编辑字段

Question

一段时间以来，我一直在研究如何在我的 iOS 应用程序中使用 PDF。我已经解决了一些难题，例如扫描运算符和在 UIWebView 中显示 PDF。但是，我真正需要做的是识别 PDF 文档中的可编辑字段。

理想情况下，我希望能够直接与字段交互，但这听起来非常困难，而且不是显而易见的第一步。我已经在与可以以这种方式操作 PDF 的 Windows 服务进行交互，并且可以满足于识别可编辑字段、在表单 View 中从用户那里收集字段数据，并将该数据发布回服务器。问题是我看不到如何识别字段。我正在处理政府颁发的 PDF，例如 I-9 和 W-4，因此我无法控制 PDF 的创建或字段的命名。这就是为什么我需要动态提取它们的原因。任何帮助和/或引用将不胜感激。

我正在使用来自 Apple 的 Quatrz 2D 的 [this reference](https://developer.apple.com/library/mac/#documentation/graphicsimaging/conceptual/drawingwithquartz2d/dq_pdf_scan/dq_pdf_scan.html“PDF Document Parsing”)扫描 PDF 时触发运算符(operator)回调的编程指南，但这并不能帮助我找到可编辑的字段。

我还简单地加载了一个 UIWebView 和 PDF 数据以显示给用户。

[_webView loadData:decodedData MIMEType:@"application/pdf" textEncodingName:@"utf-8" baseURL:nil];

更新:

我构建了一个 PDF Helper 类(如下所示)来遍历目录中所有可能的对象类型。最初我没有处理数组中的嵌套字典，所以我没有看到表单字段。一旦我解决了这个问题，我就意识到我必须考虑父引用以避免会启动无限循环的循环递归调用。下面的代码显示了文档目录中的大量信息。现在我只需要解析它来隔离我需要的表单字段。

PDFHelper.h

#import <Foundation/Foundation.h>

id selfClass;

@interface PDFHelper : NSObject

@property (nonatomic, strong) NSData *pdfData;
@property (nonatomic, strong) NSMutableDictionary *pdfDict;
@property (nonatomic) int catalogLevel;


-(NSArray *) copyPDFArray:(CGPDFArrayRef)arr referencingDictionary:(CGPDFDictionaryRef)dict referencingKey:(const char *)key;
-(NSArray *) getFormFields;
-(CGPDFDictionaryRef) getDocumentCatalog;

@end

PDFHelper.m

#import "PDFHelper.h"
#import "FileHelpers.h"
#import "Log.h"

@implementation PDFHelper

@synthesize pdfData = _pdfData;
@synthesize pdfDict = _pdfDict;
@synthesize catalogLevel = _catalogLevel;

-(id)init
{
    self = [super init];
    if(self)
    {
        selfClass = self;
        _pdfDict = [[NSMutableDictionary alloc] init];
        _catalogLevel = 1;
    }

    return self;
}

-(NSArray *) getFormFields
{
    CGPDFDictionaryRef acroForm = NULL;
    if (CGPDFDictionaryGetDictionary([self getPdfDocDictionary], "AcroForm", &acroForm))
        CGPDFDictionaryApplyFunction(acroForm, getDictionaryObjects, acroForm);
    return [_pdfDict objectForKey:@"XFA"];
}

-(CGPDFDictionaryRef) getDocumentCatalog
{
    CGPDFDictionaryRef docCatalog = [self getPdfDocDictionary];
    CGPDFDictionaryApplyFunction(docCatalog, getDictionaryObjects, docCatalog);
    return docCatalog;
}

-(CGPDFDictionaryRef) getPdfDocDictionary
{
    NSURL *pdf = [[NSURL alloc] initFileURLWithPath:[FileHelpers pathInLibraryDirectory:@"file.pdf"]];

    [_pdfData writeToFile:[pdf path] atomically:YES];

    CGPDFDocumentRef pdfDocument = CGPDFDocumentCreateWithURL((__bridge CFURLRef)pdf);
    CGPDFDictionaryRef returnDict = CGPDFDocumentGetCatalog(pdfDocument);
    return returnDict;
}

void getDictionaryObjects (const char *key, CGPDFObjectRef object, void *info) {

    NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"key: %s", key]];
    for (int i = 0; i < [selfClass catalogLevel]; i++)
        logString = [NSString stringWithFormat:@"-%@", logString];
    [Log LogDebug:logString];

    CGPDFDictionaryRef contentDict = (CGPDFDictionaryRef)info;

    CGPDFObjectType type = CGPDFObjectGetType(object);
    switch (type) {
        case kCGPDFObjectTypeNull: {            
                [Log LogDebug:[NSString stringWithFormat:@"*****pdf null value"]];
            break;
        }
        case kCGPDFObjectTypeBoolean: {
            CGPDFBoolean objectBoolean;
            if (CGPDFObjectGetValue(object, kCGPDFObjectTypeBoolean, &objectBoolean)) {
                NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf boolean value: %@", [NSNumber numberWithBool:objectBoolean]]];
                for (int i = 0; i < [selfClass catalogLevel]; i++)
                    logString = [NSString stringWithFormat:@"-%@", logString];
                [Log LogDebug:logString];
                [[selfClass pdfDict] setObject:[NSNumber numberWithBool:objectBoolean]
                                        forKey:[NSString stringWithCString:key encoding:NSUTF8StringEncoding]];
            }
            break;
        }
        case kCGPDFObjectTypeInteger: {
            CGPDFInteger objectInteger;
            if (CGPDFObjectGetValue(object, kCGPDFObjectTypeInteger, &objectInteger)) {
                NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf integer value: %ld", (long int)objectInteger]];
                for (int i = 0; i < [selfClass catalogLevel]; i++)
                    logString = [NSString stringWithFormat:@"-%@", logString];
                [Log LogDebug:logString];
                [[selfClass pdfDict] setObject:[NSNumber numberWithInt:objectInteger]
                                        forKey:[NSString stringWithCString:key encoding:NSUTF8StringEncoding]];
            }
            break;
        }
        case kCGPDFObjectTypeReal: {
            CGPDFReal objectReal;
            if (CGPDFObjectGetValue(object, kCGPDFObjectTypeReal, &objectReal)) {
                NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf real value: %ld", (long int)objectReal]];
                for (int i = 0; i < [selfClass catalogLevel]; i++)
                    logString = [NSString stringWithFormat:@"-%@", logString];
                [Log LogDebug:logString];
                [[selfClass pdfDict] setObject:[NSNumber numberWithInt:objectReal]
                                        forKey:[NSString stringWithCString:key encoding:NSUTF8StringEncoding]];
            }
            break;
        }
        case kCGPDFObjectTypeName: {
            const char *name;
            if (CGPDFDictionaryGetName(contentDict, key, &name))
            {
                NSString *dictName = [[NSString alloc] initWithCString:name encoding:NSUTF8StringEncoding];
                if (dictName)
                {
                    NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf name value: %@", dictName]];
                    for (int i = 0; i < [selfClass catalogLevel]; i++)
                        logString = [NSString stringWithFormat:@"-%@", logString];
                    [Log LogDebug:logString];
                    [[selfClass pdfDict] setObject:dictName
                                            forKey:[NSString stringWithCString:key encoding:NSUTF8StringEncoding]];
                }
            }
            break;
        }
        case kCGPDFObjectTypeString: {
            CGPDFStringRef objectString;
            if (CGPDFObjectGetValue(object, kCGPDFObjectTypeString, &objectString)) {
                NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf string value: %@", (__bridge NSString *)CGPDFStringCopyTextString(objectString)]];
                for (int i = 0; i < [selfClass catalogLevel]; i++)
                    logString = [NSString stringWithFormat:@"-%@", logString];
                [Log LogDebug:logString];
                [[selfClass pdfDict] setObject:(__bridge NSString *)CGPDFStringCopyTextString(objectString)
                                        forKey:[NSString stringWithCString:key encoding:NSUTF8StringEncoding]];
            }
            break;
        }
        case kCGPDFObjectTypeArray: {
            CGPDFArrayRef objectArray;
            if (CGPDFObjectGetValue(object, kCGPDFObjectTypeArray, &objectArray)) {
                NSArray *myArray=[selfClass copyPDFArray:objectArray referencingDictionary:contentDict referencingKey:key];
                [[selfClass pdfDict] setObject:myArray
                                        forKey:[NSString stringWithCString:key encoding:NSUTF8StringEncoding]];

            }
            break;
        }
        case kCGPDFObjectTypeDictionary: {
            CGPDFDictionaryRef objectDictionary;
            if (CGPDFObjectGetValue(object, kCGPDFObjectTypeDictionary, &objectDictionary)) {
                NSString *logString = @"Found dictionary";
                for (int i = 0; i < [selfClass catalogLevel]; i++)
                    logString = [NSString stringWithFormat:@"-%@", logString];
                //[Log LogDebug:logString];
                NSString *keyCheck = [[NSString alloc] initWithUTF8String:key];
                if (![keyCheck isEqualToString:@"Parent"] && ![keyCheck isEqualToString:@"P"])
                {
                    [selfClass setCatalogLevel:[selfClass catalogLevel] + 1];
                    CGPDFDictionaryApplyFunction(objectDictionary, getDictionaryObjects, objectDictionary);
                    [selfClass setCatalogLevel:[selfClass catalogLevel] - 1];
                }
            }
            break;
        }
        case kCGPDFObjectTypeStream: {
            CGPDFStreamRef objectStream;
            if (CGPDFObjectGetValue(object, kCGPDFObjectTypeStream, &objectStream)) {

                CGPDFDictionaryRef dict = CGPDFStreamGetDictionary( objectStream );

                CGPDFDataFormat fmt = CGPDFDataFormatRaw;
                CFDataRef streamData = CGPDFStreamCopyData(objectStream, &fmt);
                NSData *data = [[NSData alloc] initWithData:(__bridge NSData *)(streamData)];
                [data writeToFile:[FileHelpers pathInDocumentDirectory:@"data.dat"] atomically:YES];
                NSString *dataString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
                //if (!dataString) {
                //    dataString = [[NSString alloc] initWithData:(__bridge NSData *)(streamData) encoding:NSUTF16StringEncoding];
               // }

                NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf stream length: %ld - %@", (long int)CFDataGetLength( streamData ), dataString]];

                for (int i = 0; i < [selfClass catalogLevel]; i++)
                    logString = [NSString stringWithFormat:@"-%@", logString];
                [Log LogDebug:logString];

                NSString *keyCheck = [[NSString alloc] initWithUTF8String:key];
                if( dict && ![keyCheck isEqualToString:@"Parent"] && ![keyCheck isEqualToString:@"P"])
                {
                    [selfClass setCatalogLevel:[selfClass catalogLevel] + 1];
                    CGPDFDictionaryApplyFunction(dict, getDictionaryObjects, dict);
                    [selfClass setCatalogLevel:[selfClass catalogLevel] - 1];
                }
            }
        }
    }
}

- (NSArray *)copyPDFArray:(CGPDFArrayRef)arr referencingDictionary:(CGPDFDictionaryRef)dict referencingKey:(const char *)key
{
    int i = 0;
    NSMutableArray *temp = [[NSMutableArray alloc] init];

    NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf array count: %zu", CGPDFArrayGetCount(arr)]];
    for (int i = 0; i < [selfClass catalogLevel]; i++)
        logString = [NSString stringWithFormat:@"-%@", logString];
    [Log LogDebug:logString];

    for(i=0; i<CGPDFArrayGetCount(arr); i++){
        CGPDFObjectRef object;
        CGPDFArrayGetObject(arr, i, &object);
        CGPDFObjectType type = CGPDFObjectGetType(object);
        switch(type){
            case kCGPDFObjectTypeNull: {
                NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf array null(%d)", i]];
                for (int i = 0; i < [selfClass catalogLevel]; i++)
                    logString = [NSString stringWithFormat:@"-%@", logString];
                [Log LogDebug:logString];
                break;
            }
            case kCGPDFObjectTypeBoolean: {
                CGPDFBoolean objectBool;
                if (CGPDFObjectGetValue(object, kCGPDFObjectTypeBoolean, &objectBool)) {
                    NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf array boolean value(%d): %@", i, [NSNumber numberWithBool:objectBool]]];
                    for (int i = 0; i < [selfClass catalogLevel]; i++)
                        logString = [NSString stringWithFormat:@"-%@", logString];
                    [Log LogDebug:logString];
                    [temp addObject:[NSNumber numberWithBool:objectBool]];
                }
                break;
            }
            case kCGPDFObjectTypeInteger: {
                CGPDFInteger objectInteger;
                if (CGPDFObjectGetValue(object, kCGPDFObjectTypeInteger, &objectInteger)) {
                    NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf array integer value(%d): %ld", i, (long int)objectInteger]];
                    for (int i = 0; i < [selfClass catalogLevel]; i++)
                        logString = [NSString stringWithFormat:@"-%@", logString];
                    [Log LogDebug:logString];
                    [temp addObject:[NSNumber numberWithInt:objectInteger]];
                }
                break;
            }
            case kCGPDFObjectTypeReal:
            {
                CGPDFReal objectReal;
                if (CGPDFObjectGetValue(object, kCGPDFObjectTypeReal, &objectReal))
                {
                    NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf array real(%d): %ld", i, (long int)objectReal]];
                    for (int i = 0; i < [selfClass catalogLevel]; i++)
                        logString = [NSString stringWithFormat:@"-%@", logString];
                    [Log LogDebug:logString];
                    [temp addObject:[NSNumber numberWithInt:objectReal]];
                }
                break;
            }
            case kCGPDFObjectTypeName:
            {
                const char *name;
                if (CGPDFDictionaryGetName(dict, key, &name))
                {
                    NSString *dictName = [[NSString alloc] initWithCString:name encoding:NSUTF8StringEncoding];

                    if (dictName)
                    {
                        NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf array name value(%d): %@", i, dictName]];
                        for (int i = 0; i < [selfClass catalogLevel]; i++)
                            logString = [NSString stringWithFormat:@"-%@", logString];
                        [Log LogDebug:logString];
                        [[selfClass pdfDict] setObject:dictName
                                                forKey:[NSString stringWithCString:key encoding:NSUTF8StringEncoding]];
                    }
                }
                break;
            }
            case kCGPDFObjectTypeString:
            {
                CGPDFStringRef objectString;
                if (CGPDFObjectGetValue(object, kCGPDFObjectTypeString, &objectString))
                {
                    NSString *tempStr = (__bridge NSString *)CGPDFStringCopyTextString(objectString);
                    NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf array string(%d): %@", i, tempStr]];
                    for (int i = 0; i < [selfClass catalogLevel]; i++)
                        logString = [NSString stringWithFormat:@"-%@", logString];
                    [Log LogDebug:logString];
                    [temp addObject:tempStr];
                }
                break;
            }
            case kCGPDFObjectTypeArray :
            {
                CGPDFArrayRef objectArray;
                if (CGPDFObjectGetValue(object, kCGPDFObjectTypeArray, &objectArray))
                {
                    NSArray *tempArr = [selfClass copyPDFArray:objectArray referencingDictionary:dict referencingKey:key];
                    [temp addObject:tempArr];
                }
                break;
            }
            case kCGPDFObjectTypeDictionary :
            {
                CGPDFDictionaryRef objectDict;
                NSString *keyCheck = [[NSString alloc] initWithUTF8String:key];
                if (CGPDFObjectGetValue(object, kCGPDFObjectTypeDictionary, &objectDict) && ![keyCheck isEqualToString:@"Parent"] && ![keyCheck isEqualToString:@"P"])
                {
                    [selfClass setCatalogLevel:[selfClass catalogLevel] + 1];
                    CGPDFDictionaryApplyFunction( objectDict, getDictionaryObjects,  objectDict);
                    [selfClass setCatalogLevel:[selfClass catalogLevel] - 1];
                }
                break;
            }
            case kCGPDFObjectTypeStream :
            {
                CGPDFStreamRef objectStream;
                if (CGPDFObjectGetValue(object, kCGPDFObjectTypeStream, &objectStream))
                {
                    CGPDFDictionaryRef streamDict = CGPDFStreamGetDictionary( objectStream );
                    CGPDFDataFormat fmt = CGPDFDataFormatRaw;
                    CFDataRef streamData = CGPDFStreamCopyData(objectStream, &fmt);
                    NSString *dataString = [[NSString alloc] initWithData:(__bridge NSData *)(streamData) encoding:NSUTF8StringEncoding];

                    NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"pdf array stream length: (%d): %ld - %@", i, (long int)CFDataGetLength( streamData ), dataString]];

                    for (int i = 0; i < [selfClass catalogLevel]; i++)
                        logString = [NSString stringWithFormat:@"-%@", logString];
                    [Log LogDebug:logString];


                    NSString *keyCheck = [[NSString alloc] initWithUTF8String:key];
                    if( streamDict && ![keyCheck isEqualToString:@"Parent"] && ![keyCheck isEqualToString:@"P"])
                    {
                        [selfClass setCatalogLevel:[selfClass catalogLevel] + 1];
                        CGPDFDictionaryApplyFunction( streamDict, getDictionaryObjects, streamDict );
                        [selfClass setCatalogLevel:[selfClass catalogLevel] - 1];
                    }
                }
            }

        }
    }
    return temp;
}

@end

Answer 1

“可编辑字段”是指可以使用 Acrobat 或 Adob​​e Reader 填写的表单元素类型？

这些字段不是实际页面描述的一部分。如果您查看 PDF 规范文档，您会在第 12.7 章中找到对“交互式表单”的描述，其中解释了文档的字段字典是从文档目录中名为“AcroForm”的元素开始存储的。

据我所知，iOS 确实允许您访问文档目录，因此您必须在该目录字典中找到“AcroForm”字段，然后进入字段字典结构以收集您想要的信息。完整文档中的所有字段都以分层方式存储在这个地方。