iOS：请求访问相机

Question

我有一个带有二维码扫描仪的应用程序可以正常工作，但在 iOS 8 上，对相机的默认访问是“拒绝”。因此，我必须进入设置并手动授予应用程序使用相机的权限。如何制作提示“您愿意授予此应用使用相机的权限”之类的提示吗？

这是我的代码示例，它检查相机权限，然后在用户未授予权限时请求权限。但是，授予权限的链接永远不会出现，最终只会显示 UIAlertView。我测试时状态确实是DENIED，那么它没有请求权限是有原因的吗？谢谢！

我还有#import AVFoundation/AVFoundation.h 所以这不是问题。

-(void) checkCameraAuthorization {

AVAuthorizationStatus status = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];

if(status == AVAuthorizationStatusAuthorized) { // authorized
    NSLog(@"camera authorized");
}
else if(status == AVAuthorizationStatusDenied){ // denied
    if ([AVCaptureDevice respondsToSelector:@selector(requestAccessForMediaType: completionHandler:)]) {
        [AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {
            // Will get here on both iOS 7 & 8 even though camera permissions weren't required
            // until iOS 8. So for iOS 7 permission will always be granted.

            NSLog(@"DENIED");

            if (granted) {
                // Permission has been granted. Use dispatch_async for any UI updating
                // code because this block may be executed in a thread.
                dispatch_async(dispatch_get_main_queue(), ^{
                    //[self doStuff];
                });
            } else {
                // Permission has been denied.
                UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Not Authorized" message:@"Please go to Settings and enable the camera for this app to use this feature." delegate:self cancelButtonTitle:nil otherButtonTitles:@"OK", nil];
                [alert show];
            }
        }];
    }
}
else if(status == AVAuthorizationStatusRestricted){ // restricted
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Not Authorized" message:@"Please go to Settings and enable the camera for this app to use this feature." delegate:self cancelButtonTitle:nil otherButtonTitles:@"OK", nil];
    [alert show];
}
else if(status == AVAuthorizationStatusNotDetermined){ // not determined

    [AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {
        if(granted){ // Access has been granted ..do something
            NSLog(@"camera authorized");
        } else { // Access denied ..do something
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Not Authorized" message:@"Please go to Settings and enable the camera for this app to use this feature." delegate:self cancelButtonTitle:nil otherButtonTitles:@"OK", nil];
            [alert show];
        }
    }];
}
}

Answer 1

听起来该应用已被拒绝访问相机。在这种情况下，您无法再次提示。每次安装只能提示用户访问一次。之后，您需要将用户引导至设置。

将用户发送到可以启用相机的设置（在 iOS8 上）：

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:UIApplicationOpenSettingsURLString]];

如果您正在测试，请尝试从手机中删除该应用，然后重新安装并运行它。这会让您回到 AVAuthorizationStatusNotDetermined 状态。

Answer 2

对于 Swift 3：

UIApplication.shared.openURL(URL(string: UIApplicationOpenSettingsURLString)!)

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