ios7新增基础类库以及OC新特性

新特性：

Modules：用XCode5新建工程默认支持modules编译，老项目需在Build Settings里查找modules，找到的Enable Modules选项设置为YES。

对应新增语法：@import，导入系统头文件，例如：@import MapKit;  或者库的部分头文件：@import UIKit.UIView;

优点：不需要再在Build Phases里的Link Binary With Libraries添加系统framework文件；缺点：不支持自定义或第三方库

新返回类型：instancetype，用在构造函数返回类型上，建议以前用id作为返回类型的都改成instancetype。

好处：有更严格的编译类型检查，便于编译时即可发现潜在的问题；

NSArray：新增函数： -(id)firstObject; 但只要ios4以上都可以用

NSData：新增Base64编码，相应的函数有：

- (id)initWithBase64EncodedString:(NSString *)base64String
      options:(NSDataBase64DecodingOptions)options;
 
- (NSString *)base64EncodedStringWithOptions:
      (NSDataBase64EncodingOptions)options;
 
- (id)initWithBase64EncodedData:(NSData *)base64Data
      options:(NSDataBase64DecodingOptions)options;
 
- (NSData *)base64EncodedDataWithOptions:
      (NSDataBase64EncodingOptions)options;

NSTimer：新增函数：

- (NSTimeInterval)tolerance;
- (void)setTolerance:(NSTimeInterval)tolerance;

设置tolerance对于启动若干个fireDate相近的NSTimer有用，节省CPU唤醒时间

NSCharacterSet新增函数：

• + (id)URLUserAllowedCharacterSet
• + (id)URLPasswordAllowedCharacterSet
• + (id)URLHostAllowedCharacterSet
• + (id)URLPathAllowedCharacterSet
• + (id)URLQueryAllowedCharacterSet
• + (id)URLFragmentAllowedCharacterSet

新增类：

NSProgress：进度通知类

NSURLComponents：可把其视作NSMutableURL，例子：

NSURLComponents *components = [NSURLComponents componentsWithString:@"http://nshipster.com"];
components.path = @"/iOS7";
components.query = @"foo=bar";

NSLog(@"%@", components.scheme); // @"http"
NSLog(@"%@", [components URL]); // @"http://nshipster.com/iOS7?foo=bar"

CIDetectorSmile & CIDetectorEyeBlink：图像微笑和眨眼识别，例子：

CIDetector *smileDetector = [CIDetector detectorOfType:CIDetectorTypeFace
                                context:context
                                options:@{CIDetectorTracking: @YES,
                                          CIDetectorAccuracy: CIDetectorAccuracyLow}];
NSArray *features = [smileDetector featuresInImage:image options:@{CIDetectorSmile:@YES}];
if (([features count] > 0) && (((CIFaceFeature *)features[0]).hasSmile)) {
    UIImageWriteToSavedPhotosAlbum(image, self, @selector(didFinishWritingImage), features);
} else {
    self.label.text = @"Say Cheese!"
}

AVCaptureMetaDataOutput：支持二维码及其他类型码识别，例子：

AVCaptureSession *session = [[AVCaptureSession alloc] init];
AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSError *error = nil;

AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device
                                                                    error:&error];
if (input) {
    [session addInput:input];
} else {
    NSLog(@"Error: %@", error);
}

AVCaptureMetadataOutput *output = [[AVCaptureMetadataOutput alloc] init];
[output setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];
[output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
[session addOutput:output];

[session startRunning];

#pragma mark - AVCaptureMetadataOutputObjectsDelegate

- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputMetadataObjects:(NSArray *)metadataObjects
       fromConnection:(AVCaptureConnection *)connection
{
    NSString *QRCode = nil;
    for (AVMetadataObject *metadata in metadataObjects) {
        if ([metadata.type isEqualToString:AVMetadataObjectTypeQRCode]) {
            // This will never happen; nobody has ever scanned a QR code... ever
            QRCode = [(AVMetadataMachineReadableCodeObject *)metadata stringValue];
            break;
        }
    }

    NSLog(@"QR Code: %@", QRCode);
}

SSReadingList：添加URL到safari阅读列表中，例子：

NSURL *URL = [NSURL URLWithString:@"http://nshipster.com/ios7"];
[[SSReadingList defaultReadingList] addReadingListItemWithURL:URL
                                                        title:@"NSHipster"
                                                  previewText:@"..."
                                                        error:nil];

AVSpeechSynthesizer：文本转语音，例子：

AVSpeechSynthesizer *synthesizer = [[AVSpeechSynthesizer alloc] init];
AVSpeechUtterance *utterance = [AVSpeechUtterance speechUtteranceWithString:@"Just what do you think you're doing, Dave?"];
utterance.rate = AVSpeechUtteranceMinimumSpeechRate; // Tell it to me slowly
[synthesizer speakUtterance:utterance];

MKDistanceFormatter：距离格式化为本地文本，例子：

CLLocation *sanFrancisco = [[CLLocation alloc] initWithLatitude:37.775 longitude:-122.4183333];
CLLocation *portland = [[CLLocation alloc] initWithLatitude:45.5236111 longitude:-122.675];
CLLocationDistance distance = [portland distanceFromLocation:sanFrancisco];

MKDistanceFormatter *formatter = [[MKDistanceFormatter alloc] init];
formatter.units = MKDistanceFormatterUnitsImperial;
NSLog(@"%@", [formatter stringFromDistance:distance]); // 535 miles

参考网址：
http://nshipster.com/ios7/

http://www.raywenderlich.com/49850/whats-new-in-objective-c-and-foundation-in-ios-7