如何使用UIImagePickerControllerDelegate在viewDidLoad上啟動相機？

Question

我在Swift中有一個新的iOS應用程序，我試圖在應用程序啟動后立即顯示相機。 在我的視圖控制器中，我有一個UIView對象，我嘗試用相機填充。

我的視圖控制器中的代碼在viewDidLoad方法中調用UIImagePickerController但沒有任何反應。

這是代碼，任何想法為什么沒有發生？ 是不是應該在應用程序啟動時使用此代碼打開相機？

import UIKit

class ViewController: UIViewController, UINavigationControllerDelegate, UIImagePickerControllerDelegate {
    let imagePicker = UIImagePickerController()
    @IBOutlet weak var imageViewer: UIImageView!

    override func viewDidLoad() {
        super.viewDidLoad()
        if UIImagePickerController.isCameraDeviceAvailable(   UIImagePickerControllerCameraDevice.Front) {
            imagePicker.delegate = self
            imagePicker.sourceType = UIImagePickerControllerSourceType.Camera
            presentViewController(imagePicker, animated: true, completion: nil)
        } else {
            println("no front camera available")
        }

        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func imagePickerController(picker: UIImagePickerController, didFinishPickingImage image: UIImage!, editingInfo: [NSObject : AnyObject]!) {
        dismissViewControllerAnimated(true, completion: nil)
        imageViewer.image = image
    }
}

更新 ：如果我在故事板上添加一個按鈕，將其連接到代碼並將viewDidLoad中的代碼放入其中，單擊該按鈕時相機將工作：

@IBAction func presentImagePicker(sender: AnyObject) {

    if UIImagePickerController.isCameraDeviceAvailable( UIImagePickerControllerCameraDevice.Front) {
        imagePicker.delegate = self
        imagePicker.sourceType = UIImagePickerControllerSourceType.Camera
        presentViewController(imagePicker, animated: true, completion: nil)
    }
}

我知道相機可以正常工作，但是如何讓它無需按下按鈕就能正常工作？

Answer 1

這是您的解決方案。

以這種方式將您的代碼放在viewDidAppear方法中：

override func viewDidAppear(animated: Bool) {

    if UIImagePickerController.isCameraDeviceAvailable( UIImagePickerControllerCameraDevice.Front) {
        imagePicker.delegate = self
        imagePicker.sourceType = UIImagePickerControllerSourceType.Camera
        presentViewController(imagePicker, animated: true, completion: nil)
    }
}

這將在您的應用啟動時加載相機。

嘗試在viewDidLoad中執行此操作將無法工作，因為在首次創建視圖后調用它，並且視圖不是該點上任何其他內容的子視圖。

Answer 2

override func viewDidLoad() {

 if UIImagePickerController.isCameraDeviceAvailable( UIImagePickerControllerCameraDevice.Front) {
    imagePicker.delegate = self
    imagePicker.sourceType = UIImagePickerControllerSourceType.Camera
    presentViewController(imagePicker, animated: true, completion: nil)
 }
}