Objective-C中架构x86_64的未定义符号

Question

我正在尝试在Xcode项目中实现此处的AVFoundation示例代码:http://developer.apple.com/library/mac/#qa/qa1740/_index.html#//apple_ref/doc/uid/DTS40011007

我所做的唯一修改是删除对autorelease,release和retain的引用,因为我为项目启用了自动引用计数.成功解决了这些构建错误后,我现在收到"架构x86_64的未定义符号".

我在Mountain Lion 10.8上运行,并且在将AVFoundation.h导入我的头文件时没有出错,但似乎没有找到AV*符号？

下面是错误日志,.h和.m代码.更有知识的人可以帮助我找出问题所在吗？

日志:

Undefined symbols for architecture x86_64:
  "_AVCaptureSessionPresetMedium", referenced from:
      -[Recorder screenRecording:] in screenAppDelegate.o
  "_OBJC_CLASS_$_AVCaptureMovieFileOutput", referenced from:
      objc-class-ref in screenAppDelegate.o
  "_OBJC_CLASS_$_AVCaptureScreenInput", referenced from:
      objc-class-ref in screenAppDelegate.o
  "_OBJC_CLASS_$_AVCaptureSession", referenced from:
      objc-class-ref in screenAppDelegate.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

.H

#import <Cocoa/Cocoa.h>
#import <Foundation/Foundation.h>
#import <AVFoundation/AVFoundation.h>

@interface screenAppDelegate : NSObject <NSApplicationDelegate>
@end

@interface Recorder : NSObject <AVCaptureFileOutputRecordingDelegate> {
    @private AVCaptureSession *mSession;
    AVCaptureMovieFileOutput *mMovieFileOutput;
    NSTimer *mTimer;
}

-(void)screenRecording:(NSURL *)destPath;

@end

.M

#import "screenAppDelegate.h"

@implementation screenAppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    // Insert code here to initialize your application
}

@end


@implementation Recorder

-(void)screenRecording:(NSURL *)destPath 
{
    // Create a capture session
    mSession = [[AVCaptureSession alloc] init];

    // Set the session preset as you wish
    mSession.sessionPreset = AVCaptureSessionPresetMedium;

    // If you're on a multi-display system and you want to capture a secondary display,
    // you can call CGGetActiveDisplayList() to get the list of all active displays.
    // For this example, we just specify the main display.
    CGDirectDisplayID displayId = kCGDirectMainDisplay;

    // Create a ScreenInput with the display and add it to the session
    AVCaptureScreenInput *input = [[AVCaptureScreenInput alloc] initWithDisplayID:displayId];
    if (!input) {
        //[mSession release];
        mSession = nil;
        return;
    }
    if ([mSession canAddInput:input])
        [mSession addInput:input];

    // Create a MovieFileOutput and add it to the session
    mMovieFileOutput = [[AVCaptureMovieFileOutput alloc] init];
    if ([mSession canAddOutput:mMovieFileOutput])
        [mSession addOutput:mMovieFileOutput];

    // Start running the session
    [mSession startRunning];

    // Delete any existing movie file first
    if ([[NSFileManager defaultManager] fileExistsAtPath:[destPath path]])
    {
        NSError *err;
        if (![[NSFileManager defaultManager] removeItemAtPath:[destPath path] error:&err])
        {
            NSLog(@"Error deleting existing movie %@",[err localizedDescription]);
        }
    }

    // Start recording to the destination movie file
    // The destination path is assumed to end with ".mov", for example, @"/users/master/desktop/capture.mov"
    // Set the recording delegate to self
    [mMovieFileOutput startRecordingToOutputFileURL:destPath recordingDelegate:self];

    // Fire a timer in 5 seconds
    mTimer = [NSTimer scheduledTimerWithTimeInterval:5 target:self selector:@selector(finishRecord:) userInfo:nil repeats:NO];
}

-(void)finishRecord:(NSTimer *)timer
{
    // Stop recording to the destination movie file
    [mMovieFileOutput stopRecording];

    //[mTimer release];
    mTimer = nil;
}

// AVCaptureFileOutputRecordingDelegate methods

- (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error
{
    NSLog(@"Did finish recording to %@ due to error %@", [outputFileURL description], [error description]);

    // Stop running the session
    [mSession stopRunning];

    // Release the session
    //[mSession release];
    mSession = nil;
}

Answer 1

导入头文件是不够的,还必须将AVFoundation框架添加到项目中.此错误来自链接器,而不是来自编译器本身 - 可以找到AVFoundation标头并且源文件的编译成功,但链接器无法从生成的目标文件中生成可执行文件,因为您没有告诉它(通过Xcode的设置)链接到AVFoundation框架.

请参阅有关编译过程的这篇文章,以了解发生这种情况的原因.