Windows Phone 开发——相机功能开发

　　相机功能是手机区别于PC的一大功能，在做手机应用时，如果合理的利用了拍照功能，可能会给自己的应用增色很多。使用Windows Phone的相机功能，有两种方法，一种是使用PhotoCamera类来构建自己的相机UI，另外一种是通过CameraCaptureTask选择器来实现该功能。

他们的区别是：

• PhotoCamera类允许应用控制照片属性，如 ISO、曝光补偿和手动对焦位置，应用可以对照片有更多的控制，当然也会麻烦很多。需要实现闪光灯、对焦、分辨率、快门按钮等操作。
• CameraCaptureTask拍照会调用系统的相机功能，返回一个有照片数据的返回值，同时一旦拍照，就会进入手机相册。

一. CameraCaptureTask选择器。

1. 首先需要引用

using Microsoft.Phone.Tasks;

1. 声明任务对象，需要在页面的构造函数之前声明

CameraCaptureTask cameraCaptureTask;

在构造函数中实例化CameraCaptureTask对象，并且注册回调方法。

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

在应用程序中的所需位置添加以下代码，例如按键点击事件中

cameraCaptureTask.Show();

在页面中添加已完成事件处理程序的代码。此代码在用户完成任务后运行。结果是一个 PhotoResult对象，该对象公开包含图像数据的流。

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;
    }
}

这部分比较简单，就不多讲了，给个demo吧：http://pan.baidu.com/s/1pJ0Polt

二. PhotoCamera

　　PhotoCamera是在windows phone os 7.1开始加入的，在使用之前需要给应用添加访问相机的权限，在

WMAppManifest.xml中添加ID_CAP_ISV_CAMERA

1. 创建UI

在创建取景器时，一般会使用VideoBrush，如果需要支持横竖屏的切换，则需要加入RelativeTransform，如下代码是一个典型的相机UI

<!-- 相机取景器 -->

        <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>

当然你还要考虑页面上的其他元素，比如点击取景器对焦，快门、闪光灯按钮等，这些可随个人洗好自定义。

1. 实现取景器和相关相机事件。
1. 首先实现取景器，先判断手机有没有相关的硬件设备(背部相机(主)或者前部相机)

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. 在加载时也需要实现各种操作事件

// 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. 上面加载了这么多事件，需要在离开此页面时释放：

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;

            }

        }

上面这些事件，看看名字估计也就懂了是干啥的了，这里说明下他们的执行顺序，CaptureThumbnailAvailable —>CaptureImageAvailable —>CaptureCompleted。

1. 拍出了照片后需要保存，可以保存到相机中，使用的是SavePictureToCameraRoll方法，同时可以保存到独立存储空间中，方便以后读取(如果仅仅保存在相册中，下次读取时必须使用照片选择器让用户去选择照片)：

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[];

                        int bytesRead = -;

                        // Copy the thumbnail to isolated storage.

                        while ((bytesRead = e.ImageStream.Read(readBuffer, , readBuffer.Length)) > )

                        {

                            targetStream.Write(readBuffer, , 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();

            }

        }

保存照片有两个方法：SavePicture和SavePictureToCameraRoll，前面的方法是保存到照片中心“保存的照片”中，后一种方法是保存到“本机拍照”中。

1. 对于闪光灯、对焦、分辨率以及快门都有相应的方法，从上面的代码中也可以看到快门有半按、全按、释放等事件，这里不再赘述，可以从源代码中看到相关的事件。

这个例子的demo是微软提供的，比较详细，源码如下：http://pan.baidu.com/s/1c0rIqSK

参考文章：Windows Phone 的相机和照片