Windows Phone 開發——相機功能開發

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原文:Windows Phone 開發——相機功能開發

　　相機功能是手機區別於PC的一大功能，在做手機應用時，如果合理的利用了拍照功能，可能會給自己的應用增色很多。使用Windows Phone的相機功能，有兩種方法，一種是使用PhotoCamera類來構建自己的相機UI，另外一種是通過CameraCaptureTask選取器來實現該功能。

他們的區別是：

• PhotoCamera類允許應用控制照片屬性，如 ISO、曝光補償和手動對焦位置，應用可以對照片有更多的控制，當然也會麻煩很多。需要實現閃光燈、對焦、解析度、快門按鈕等操作。
• CameraCaptureTask拍照會調用系統的相機功能，返回一個有照片資料的傳回值，同時一旦拍照，就會進入手機相簿。

 

一. CameraCaptureTask選取器。

1. 首先需要引用

using Microsoft.Phone.Tasks;

 

1. 聲明任務對象，需要在頁面的建構函式之前聲明

CameraCaptureTask cameraCaptureTask;

 

在建構函式中執行個體化CameraCaptureTask對象，並且註冊回調方法。

cameraCaptureTask = new CameraCaptureTask();cameraCaptureTask.Completed += new EventHandler<PhotoResult>(cameraCaptureTask_Completed);

 

在應用程式中的所需位置添加以下代碼，例如按鍵點擊事件中

cameraCaptureTask.Show();

 

在頁面中添加已完成事件處理常式的代碼。此代碼在使用者完成任務後運行。結果是一個 PhotoResult對象，該對象公開包含映像資料的流。

void cameraCaptureTask_Completed(object sender, PhotoResult e){    if (e.TaskResult == TaskResult.OK)    {        MessageBox.Show(e.ChosenPhoto.Length.ToString());//Code to display the photo on the page in an image control named myImage.        //System.Windows.Media.Imaging.BitmapImage bmp = new System.Windows.Media.Imaging.BitmapImage();        //bmp.SetSource(e.ChosenPhoto);        //myImage.Source = bmp;    }}

 

這部分比較簡單，就不多講了，給個demo吧：http://pan.baidu.com/s/1pJ0Polt

 

二. PhotoCamera

　　PhotoCamera是在windows phone os 7.1開始加入的，在使用之前需要給應用添加訪問相機的許可權，在

WMAppManifest.xml中添加ID_CAP_ISV_CAMERA

 

1. 建立UI

在建立取景器時，一般會使用VideoBrush，如果需要支援橫豎屏的切換，則需要加入RelativeTransform，如下代碼是一個典型的相機UI

<!-- 相機取景器 -->        <Canvas x:Name="VideoCanvas">            <Canvas.Background>                <VideoBrush x:Name="BackgroundVideoBrush" >                    <VideoBrush.RelativeTransform>                        <CompositeTransform x:Name="VideoBrushTransform" CenterY="0.5" CenterX="0.5"/>                    </VideoBrush.RelativeTransform>                </VideoBrush>            </Canvas.Background>        </Canvas>

 

當然你還要考慮頁面上的其他元素，比如點擊取景器對焦，快門、閃光燈按鈕等，這些可隨個人洗好自訂。

 

1. 實現取景器和相關相機事件。
1. 首先實現取景器，先判斷手機有沒有相關的硬體裝置(背部相機(主)或者前部相機)

if ((PhotoCamera.IsCameraTypeSupported(CameraType.Primary) == true) ||                 (PhotoCamera.IsCameraTypeSupported(CameraType.FrontFacing) == true))            {                // Initialize the camera, when available.                if (PhotoCamera.IsCameraTypeSupported(CameraType.FrontFacing))                {                    // Use front-facing camera if available.                    cam = new Microsoft.Devices.PhotoCamera(CameraType.FrontFacing);                }                else                {                    // Otherwise, use standard camera on back of device.                    cam = new Microsoft.Devices.PhotoCamera(CameraType.Primary);                }    //Set the VideoBrush source to the camera.                viewfinderBrush.SetSource(cam);            }            else            {                // The camera is not supported on the device.                this.Dispatcher.BeginInvoke(delegate()                {                    // Write message.                    txtDebug.Text = "A Camera is not available on this device.";                });                 // Disable UI.                ShutterButton.IsEnabled = false;                FlashButton.IsEnabled = false;                AFButton.IsEnabled = false;                ResButton.IsEnabled = false;            }

 

1. 在載入時也需要實現各種操作事件

// Event is fired when the PhotoCamera object has been initialized.                cam.Initialized += new EventHandler<Microsoft.Devices.CameraOperationCompletedEventArgs>(cam_Initialized);                 // Event is fired when the capture sequence is complete.                cam.CaptureCompleted += new EventHandler<CameraOperationCompletedEventArgs>(cam_CaptureCompleted);                 // Event is fired when the capture sequence is complete and an image is available.                cam.CaptureImageAvailable += new EventHandler<Microsoft.Devices.ContentReadyEventArgs>(cam_CaptureImageAvailable);                 // Event is fired when the capture sequence is complete and a thumbnail image is available.                cam.CaptureThumbnailAvailable += new EventHandler<ContentReadyEventArgs>(cam_CaptureThumbnailAvailable);                 // The event is fired when auto-focus is complete.                cam.AutoFocusCompleted += new EventHandler<CameraOperationCompletedEventArgs>(cam_AutoFocusCompleted);                 // The event is fired when the viewfinder is tapped (for focus).                viewfinderCanvas.Tap += new EventHandler<GestureEventArgs>(focus_Tapped);                 // The event is fired when the shutter button receives a half press.                CameraButtons.ShutterKeyHalfPressed += OnButtonHalfPress;                 // The event is fired when the shutter button receives a full press.                CameraButtons.ShutterKeyPressed += OnButtonFullPress;                 // The event is fired when the shutter button is released.                CameraButtons.ShutterKeyReleased += OnButtonRelease;

 

1. 上面載入了這麼多事件，需要在離開此頁面時釋放：

protected override void OnNavigatingFrom(System.Windows.Navigation.NavigatingCancelEventArgs e)        {            if (cam != null)            {                // Dispose camera to minimize power consumption and to expedite shutdown.                cam.Dispose();                 // Release memory, ensure garbage collection.                cam.Initialized -= cam_Initialized;                cam.CaptureCompleted -= cam_CaptureCompleted;                cam.CaptureImageAvailable -= cam_CaptureImageAvailable;                cam.CaptureThumbnailAvailable -= cam_CaptureThumbnailAvailable;                cam.AutoFocusCompleted -= cam_AutoFocusCompleted;                CameraButtons.ShutterKeyHalfPressed -= OnButtonHalfPress;                CameraButtons.ShutterKeyPressed -= OnButtonFullPress;                CameraButtons.ShutterKeyReleased -= OnButtonRelease;            }        }

 

上面這些事件，看看名字估計也就懂了是幹啥的了，這裡說明下他們的執行順序，CaptureThumbnailAvailable —>CaptureImageAvailable —>CaptureCompleted。

 

1. 拍出了照片後需要儲存，可以儲存到相機中，使用的是SavePictureToCameraRoll方法，同時可以儲存到隔離儲存區 (Isolated Storage)空間中，方便以後讀取(如果僅僅儲存在相簿中，下次讀取時必須使用照片選取器讓使用者去選擇照片)：

public void cam_CaptureThumbnailAvailable(object sender, ContentReadyEventArgs e)        {            string fileName = savedCounter + "_th.jpg";             try            {                // Write message to UI thread.                Deployment.Current.Dispatcher.BeginInvoke(delegate()                {                    txtDebug.Text = "Captured image available, saving thumbnail.";                });                 // Save thumbnail as JPEG to isolated storage.                using (IsolatedStorageFile isStore = IsolatedStorageFile.GetUserStoreForApplication())                {                    using (IsolatedStorageFileStream targetStream = isStore.OpenFile(fileName, FileMode.Create, FileAccess.Write))                    {                        // Initialize the buffer for 4KB disk pages.                        byte[] readBuffer = new byte[4096];                        int bytesRead = -1;                         // Copy the thumbnail to isolated storage.                        while ((bytesRead = e.ImageStream.Read(readBuffer, 0, readBuffer.Length)) > 0)                        {                            targetStream.Write(readBuffer, 0, bytesRead);                        }                    }                }                 // Write message to UI thread.                Deployment.Current.Dispatcher.BeginInvoke(delegate()                {                    txtDebug.Text = "Thumbnail has been saved to isolated storage.";                 });            }            finally            {                // Close image stream                e.ImageStream.Close();            }        }

 

儲存照片有兩個方法：SavePicture和SavePictureToCameraRoll，前面的方法是儲存到照片中心“儲存的照片”中，後一種方法是儲存到“本機拍照”中。

 

1. 對於閃光燈、對焦、解析度以及快門都有相應的方法，從上面的代碼中也可以看到快門有半按、全按、釋放等事件，這裡不再贅述，可以從原始碼中看到相關的事件。

 

這個例子的demo是微軟提供的，比較詳細，源碼如下：http://pan.baidu.com/s/1c0rIqSK

 

參考文章：Windows Phone 的相機和照片