Integrate Live Capture with Xamarin Camera Control - Xamarin C#

This tutorial shows how to use the LEADTOOLS SDK in a C# Xamarin application to access the video frames being captured live from a device's camera through a Xamarin camera control.

Required Knowledge

Get familiar with the basic steps of creating a project by reviewing the Add References and Set a License tutorial, before working on the Integrate Live Capture with Xamarin Camera Control - Xamarin C# tutorial.

Create the Project and Add the LEADTOOLS References

In Visual Studio, create a new C# Xamarin project, and add the following necessary LEADTOOLS references.

The references needed depend upon the purpose of the project. For this project, the following NuGet package are needed:

• Leadtools.Camera.Xamarin

Set the License File

The License unlocks the features needed for the project. It must be set before any toolkit function is called. For details, including tutorials for different platforms, refer to Setting a Runtime License.

There are two types of runtime licenses:

• Evaluation license, obtained at the time the evaluation toolkit is downloaded. It allows the toolkit to be evaluated.
• Deployment license. If a Deployment license file and developer key are needed, refer to Obtaining a License.

Note

Adding LEADTOOLS NuGet references and setting a license are covered in more detail in the Add References and Set a License tutorial.

Add Code to Check and Ask for Camera Permission

With the project created, the references added, and the license set, coding can begin.

In the Solution Explorer, open the MainPage.xaml.cs and ensure that the following are added to the using area at the top of the code:

using Xamarin.Essentials; 

Add the following global variable:

bool PermissionsGranted; 

Add a MainPage_Appearing() event handler to the MainPage class.

public MainPage() 
{ 
   // Keep rest of code as is 
   InitializeComponent(); 
 
   Appearing += MainPage_Appearing; 
} 

Use the code below to check the Camera permission for the application and prompt the user to enable them before loading the ContentPage with the live capture camera control.

private async void MainPage_Appearing(object sender, EventArgs e) 
{ 
   PermissionsGranted = await VerifyPermissions(); 
   if (PermissionsGranted == false) 
      return; 
   else 
      App.Current.MainPage = new LiveCapturePage(); 
} 
 
private async Task<bool> VerifyPermissions() 
{ 
   try 
   { 
      PermissionStatus status = PermissionStatus.Unknown; 
 
      // Camera permission - NOTE: Requires adding Permission to the Android Manifest and iOS pList 
      status = await Permissions.CheckStatusAsync<Permissions.Camera>(); 
      if (status != PermissionStatus.Granted) 
      { 
         await DisplayAlert("Camera Permission Required", "This app will proccess frames taken live from the device's camera", "OK"); 
         status = await Permissions.RequestAsync<Permissions.Camera>(); 
 
         if (status != PermissionStatus.Granted) 
            return false; 
      } 
 
      // All needed permissions granted 
      return true; 
   } 
   catch (Exception ex) 
   { 
      await DisplayAlert("Error", ex.ToString(), "OK"); 
      return false; 
   } 
} 

Add Application Permissions (Android)

In the Solution Explorer, right-click on <Project>.Droid project. Click Properties. In the Android Manifest tab, go to the Required Permissions section and enable the CAMERA permission.

Add Application Permissions (iOS)

In the Solution Explorer, right-click on Info.plist. Click Open With.... Select Generic PList Editor, then click OK.

Click the + button on the last row in the editor. This will be called Custom Property, with the Type set to String and an empty value. Click on the Property name and the dropdown will appear. From that dropdown select the Privacy - Photo Library Usage Description. Then enter a description into the Value column for why the application wants to access that given feature.

Initialize the Camera Control

With the project created, the references added, and the license set, coding can begin.

In Solution Explorer, right-Click on the base C# project and select Add -> New Item. Select the Content Page option and name the class LiveCapturePage.xaml

Open LiveCapturePage.xaml and add the following code inside the ContentPage to add the CameraView control, a Live Capture button, and a label to illustrate how many frames have been processed.

<ContentPage.Content> 
   <StackLayout> 
      <!--main grid container for everything--> 
      <Grid x:Name="mainGrid" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand"> 
         <Grid.ColumnDefinitions> 
            <ColumnDefinition x:Name="c0" Width="*"/> 
            <ColumnDefinition x:Name="c1" Width="*"/> 
            <ColumnDefinition x:Name="c2" Width="*"/> 
         </Grid.ColumnDefinitions> 
         <Grid.RowDefinitions> 
            <RowDefinition x:Name="r0" Height="*"/> 
            <RowDefinition x:Name="r1" Height="*"/> 
            <RowDefinition x:Name="r2" Height="*"/> 
            <RowDefinition x:Name="r3" Height="*"/> 
            <RowDefinition x:Name="r4" Height="*"/> 
            <RowDefinition x:Name="r5" Height="*"/> 
            <RowDefinition x:Name="r6" Height="*"/> 
            <RowDefinition x:Name="r7" Height="*"/> 
            <RowDefinition x:Name="r8" Height="*"/> 
         </Grid.RowDefinitions> 
         <Label x:Name="capturedFrames" Text="Frames Captured: 0" TextColor="Blue" Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="3"/> 
         <namespace:CameraView x:Name="leadCamera" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="3" Grid.RowSpan="7" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand"/> 
         <Button x:Name="liveCapture" Text="Live Capture" Grid.Row="8" Grid.Column="1" Clicked="liveCapture_Clicked"/> 
      </Grid> 
   </StackLayout> 
</ContentPage.Content> 

Right click on the page and select View Code to bring up the code behind LiveCapturePage.xaml. Add the following statements to the using block at the top of LiveCapturePage.xaml.cs.

// Using block at the top 
using System; 
using Xamarin.Forms; 
using Xamarin.Forms.Xaml; 

// Add this global variable 
private int frameCounter = 0; 

Configure the camera control by setting the CameraOptions.AutoRotateImage to true inside the LiveCapturePage() method:

public LiveCapturePage() 
{ 
   InitializeComponent(); 
   leadCamera.CameraOptions.AutoRotateImage = true; 
} 

Add the Live Capture Code

In the Solution Explorer, open LiveCapturePage.xaml.cs . Add a new Clicked event handler for liveCapture, if it does not already exist. Add the below code inside the handler to hook the camera control to an event handler that will process every frame taken by the capture and increment the counter by one.

private void liveCapture_Clicked(object sender, EventArgs e) 
{ 
   // Tapping the Live Capture button will hook the FrameReceived Event handler, allowing processing each frame 
   if (liveCapture.Text == "Live Capture") 
   { 
      liveCapture.Text = "Stop"; 
      leadCamera.FrameReceived += LeadCamera_FrameReceived; 
   } 
   else 
   { 
      liveCapture.Text = "Live Capture"; 
      leadCamera.FrameReceived -= LeadCamera_FrameReceived; 
   } 
} 
 
private void LeadCamera_FrameReceived(Leadtools.Camera.Xamarin.FrameHandlerEventArgs e) 
{ 
   // Frame Received Handler Code 
   frameCounter = frameCounter + 1; 
   Device.BeginInvokeOnMainThread(() => 
   { 
      capturedFrames.Text = $"Frames Processed: {frameCounter}"; 
   }); 
} 

Run the Project

Select the desired project (iOS or Android) and run the project by pressing F5, or by selecting Debug -> Start Debugging.

If the steps were followed correctly, the application runs and it will ask to allow Camera permissions which is required. For testing, click the Live Capture button at the bottom of the device's screen. A preview from the device's camera will be displayed in the CameraView and the number of frames processed will increment for every frame processed. Click the Stop button to end the preview.

Wrap-up

This tutorial showed how to use the CameraView class to process frames taken by the device's camera.

See Also

• LEADTOOLS CameraView Documentation
• LEADTOOLS SDK Download