问题：Undefined symbols for architecture armv7

Undefined symbols for architecture armv7:
"_AVMediaTypeVideo", referenced from:
-[ZBarReaderViewImpl _initWithImageScanner:] in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_AVCaptureSessionRuntimeErrorNotification", referenced from:
-[ZBarReaderViewImpl _initWithImageScanner:] in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_AVCaptureSessionDidStopRunningNotification", referenced from:
-[ZBarReaderViewImpl _initWithImageScanner:] in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_AVCaptureSessionInterruptionEndedNotification", referenced from:
-[ZBarReaderViewImpl _initWithImageScanner:] in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_AVCaptureSessionDidStartRunningNotification", referenced from:
-[ZBarReaderViewImpl _initWithImageScanner:] in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_OBJC_CLASS_$_AVCaptureSession", referenced from:
objc-class-ref in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_AVCaptureSessionWasInterruptedNotification", referenced from:
-[ZBarReaderViewImpl _initWithImageScanner:] in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_OBJC_CLASS_$_AVCaptureDeviceInput", referenced from:
objc-class-ref in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_AVLayerVideoGravityResizeAspectFill", referenced from:
-[ZBarReaderViewImpl initSubviews] in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_OBJC_CLASS_$_AVCaptureVideoPreviewLayer", referenced from:
objc-class-ref in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_AVCaptureSessionPreset640x480", referenced from:
-[ZBarReaderViewImpl _initWithImageScanner:] in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_OBJC_CLASS_$_AVCaptureDevice", referenced from:
objc-class-ref in libzbar.a(ZBarReaderViewImpl_Capture.o)
"_OBJC_CLASS_$_AVCaptureVideoDataOutput", referenced from:
objc-class-ref in libzbar.a(ZBarCaptureReader.o)
"_AVCaptureSessionErrorKey", referenced from:
-[ZBarReaderViewImpl onVideoError:] in libzbar.a(ZBarReaderViewImpl_Capture.o)
ld: symbol(s) not found for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)

解决方案：

找不到某个类的framework，查看你是不是引用了没有加到building Phase里的framework的类。此处缺少了AVFoundation.framework，添加即可。

添加动态库步骤：
targets——>build phases——>link binary with libraries——>选择要添加的库