从ios7开始，用户可以在设置->隐私->中开启或关闭某些系统权限，比如访问相册，相机 ，通讯录，地图，麦克风等。因此，在我们的程序中，如果要访问系统的某些功能，则最好判断一下权限是否开启。否则用户不能正常使用，也一头雾水，还以为程序出错了。

访问摄像头：

需要导入

#import <AVFoundation/AVFoundation.h>

if(isIOS7AndLater) {NSString *mediaType = AVMediaTypeVideo;// Or AVMediaTypeAudioAVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:mediaType];NSLog(@"---cui--authStatus--------%d",authStatus);// This status is normally not visible—the AVCaptureDevice class methods for discovering devices do not return devices the user is restricted from accessing.if(authStatus ==AVAuthorizationStatusRestricted){NSLog(@"Restricted");}else if(authStatus == AVAuthorizationStatusDenied){// The user has explicitly denied permission for media capture.NSLog(@"Denied");     //应该是这个，如果不允许的话UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"提示"message:@"请在设备的"设置-隐私-相机"中允许访问相机。"delegate:selfcancelButtonTitle:@"确定"otherButtonTitles:nil];[alert show];[alert release];return;}else if(authStatus == AVAuthorizationStatusAuthorized){//允许访问// The user has explicitly granted permission for media capture, or explicit user permission is not necessary for the media type in question.NSLog(@"Authorized");}else if(authStatus == AVAuthorizationStatusNotDetermined){// Explicit user permission is required for media capture, but the user has not yet granted or denied such permission.[AVCaptureDevice requestAccessForMediaType:mediaType completionHandler:^(BOOL granted) {if(granted){//点击允许访问时调用//用户明确许可与否，媒体需要捕获，但用户尚未授予或拒绝许可。NSLog(@"Granted access to %@", mediaType);}else {NSLog(@"Not granted access to %@", mediaType);}}];}else {NSLog(@"Unknown authorization status");}
}

麦克风权限检测：

      //检测麦克风功能是否打开[[AVAudioSessionsharedInstance]requestRecordPermission:^(BOOL granted) {if (!granted){[ViewUtilalertViewWithString:NSLocalizedString(@"麦克风功能未开启",nil)];}else{[selfrecord:sender];}}];

相册权限检测：需要

#import <AssetsLibrary/AssetsLibrary.h> //导入此类和AssetsLibrary.framework框架

int author = [ALAssetsLibrary authorizationStatus];NSLog(@"author type:%d",author);if(author == ALAuthorizationStatusRestricted || author == ALAuthorizationStatusDenied) {// The user has explicitly denied permission for media capture.UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"无法使用相册"message:@"请在iPhone的\"设置-隐私-照片\"中允许访问照片。"delegate:selfcancelButtonTitle:@"确定"otherButtonTitles:nil];[alert show];[alert release];return;

ALAssetsLibrary详解

ALAssetsLibrary类是代表系统中整个资源库，使用它可以访问资源库中的资源和保存照片，视频等功能。

    _library = [[ALAssetsLibrary alloc]init];
    //判断当前应用是否能访问相册资源
    /*
     typedef NS_ENUM(NSInteger, ALAuthorizationStatus) {
     ALAuthorizationStatusNotDetermined = 0, 用户尚未做出了选择这个应用程序的问候
     ALAuthorizationStatusRestricted,        此应用程序没有被授权访问的照片数据。可能是家长控制权限。

     ALAuthorizationStatusDenied,            用户已经明确否认了这一照片数据的应用程序访问.
     ALAuthorizationStatusAuthorized         用户已授权应用访问照片数据.
     }
     */

    int author = [ALAssetsLibrary authorizationStatus];
    NSLog(@"author type:%d",author);

    //关闭监听共享照片流产生的频繁通知信息
    [ALAssetsLibrary disableSharedPhotoStreamsSupport];
    
    //创建一个相册到相册资源中，并通过block返回创建成功的相册ALAssetsGroup
    [_library addAssetsGroupAlbumWithName:@"test" resultBlock:^(ALAssetsGroup *group) {
        //NSString *const ALAssetsGroupPropertyName;
        //NSString *const ALAssetsGroupPropertyType;
        //NSString *const ALAssetsGroupPropertyPersistentID;
        //NSString *const ALAssetsGroupPropertyURL;
        //查看相册的名字
        NSLog(@"ALAssetsGroupPropertyName:%@",[group valueForProperty:ALAssetsGroupPropertyName]);
        //查看相册的类型
        NSLog(@"ALAssetsGroupPropertyType:%@",[group valueForProperty:ALAssetsGroupPropertyType]);
        //查看相册的存储id
        NSLog(@"ALAssetsGroupPropertyPersistentID:%@",[group valueForProperty:ALAssetsGroupPropertyPersistentID]);
        //查看相册存储的位置地址
        NSLog(@"ALAssetsGroupPropertyURL:%@",[group valueForProperty:ALAssetsGroupPropertyURL]);
        groupURL = [group valueForProperty:ALAssetsGroupPropertyURL];

    } failureBlock:^(NSError *error) {
        
    }];

新添加了一个名为test的相册

  [NSThread sleepForTimeInterval:0.5];
    //通过url地址在相册资源中获取该地址的资源文件ALAsset，有可能是相片或视频
    [_library assetForURL:[NSURL URLWithString:@""] resultBlock:^(ALAsset *asset) {
        /*
         NSString *const ALAssetPropertyType;
         NSString *const ALAssetPropertyLocation;
         NSString *const ALAssetPropertyDuration;
         NSString *const ALAssetPropertyOrientation;
         NSString *const ALAssetPropertyDate;
         NSString *const ALAssetPropertyRepresentations;
         NSString *const ALAssetPropertyURLs;
         NSString *const ALAssetPropertyAssetURL;
         */
        //查看资源的地理位置信息
        NSLog(@"ALAssetPropertyLocation:%@",[asset valueForProperty:ALAssetPropertyLocation]);
        //如果资源是视频，查看视频的时长
        NSLog(@"ALAssetPropertyDuration:%@",[asset valueForProperty:ALAssetPropertyDuration]);
        //查看资源的方向，图片的旋转方向
        NSLog(@"ALAssetPropertyOrientation:%@",[asset valueForProperty:ALAssetPropertyOrientation]);
        //查看资源的创建时间
        NSLog(@"ALAssetPropertyDate:%@",[asset valueForProperty:ALAssetPropertyDate]);
        //查看资源的描述信息
        NSLog(@"ALAssetPropertyRepresentations:%@",[asset valueForProperty:ALAssetPropertyRepresentations]);
        NSLog(@"ALAssetPropertyURLs:%@",[asset valueForProperty:ALAssetPropertyURLs]);
        //查看资源的url路径
        NSLog(@"ALAssetPropertyAssetURL:%@",[asset valueForProperty:ALAssetPropertyAssetURL]);
    } failureBlock:^(NSError *error) {
        
    }];
    //通过url地址获取相册资源中的一个相册
    [_library groupForURL:groupURL resultBlock:^(ALAssetsGroup *group) {
        NSLog(@"ALAssetsGroupPropertyName:%@",[group valueForProperty:ALAssetsGroupPropertyName]);
    } failureBlock:^(NSError *error) {
    
    }];
    //根据选择的类型遍历相册资源中的相对应类型的所有相册，其中stop行参是指针，表示是否停止迭代，当赋值为false则停止
    /*
     enum {
     ALAssetsGroupLibrary        = (1 << 0),
     ALAssetsGroupAlbum          = (1 << 1),
     ALAssetsGroupEvent          = (1 << 2),
     ALAssetsGroupFaces          = (1 << 3),
     ALAssetsGroupSavedPhotos    = (1 << 4),
     ALAssetsGroupPhotoStream    = (1 << 5),
     ALAssetsGroupAll            = 0xFFFFFFFF,
     };
     */
    [_library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
        NSLog(@"group name:%@",[group valueForProperty:ALAssetsGroupPropertyName]);
    } failureBlock:^(NSError *error) {
        
    }];
    //保存图片到系统默认的相册中，使用nsdata的形式，并返回照片的url地址
    [_library writeImageDataToSavedPhotosAlbum:nil metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {
        
    }];
    //保存图片到系统默认的相册中，使用cgimageref的形式，并返回照片的url地址
    [_library writeImageToSavedPhotosAlbum:nil metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {
        
    }];
    
    //保存图片到系统默认的相册中，使用cgimageref的形式，并且选择图片以什么旋转方向的形式保存，并返回照片的url地址
    /*
     typedef enum {
     ALAssetOrientationUp,            // default orientation
     ALAssetOrientationDown,          // 180 deg rotation
     ALAssetOrientationLeft,          // 90 deg CCW
     ALAssetOrientationRight,         // 90 deg CW
     ALAssetOrientationUpMirrored,    // as above but image mirrored along other axis. horizontal flip
     ALAssetOrientationDownMirrored,  // horizontal flip
     ALAssetOrientationLeftMirrored,  // vertical flip
     ALAssetOrientationRightMirrored, // vertical flip
     } ALAssetOrientation;
     */
    UIImage* image = [UIImage imageNamed:@"test.png"];
    [_library writeImageToSavedPhotosAlbum:[image CGImage] orientation:ALAssetOrientationLeft completionBlock:^(NSURL *assetURL, NSError *error) {
        NSLog(@"save image:%@",assetURL);
    }];