How to Perform OCR on Android in .NET MAUI
.NET MAUI (Multi-platform App UI) is an evolution of the Xamarin.Forms framework, designed to create cross-platform apps for Android, iOS, macOS, and Windows using .NET. .NET MAUI aims to simplify the process of building native user interfaces that can run on multiple platforms.
The IronOcr.Android package brings OCR support to Android!!
How to use IronOCR on Android in .NET MAUI
IronOCR Android Package
The IronOcr.Android package enables OCR features on Android devices via .NET cross-platform projects. The vanilla IronOCR package is not needed.
PM > Install-Package IronOcr.Android
Install with NuGet
Install-Package IronOcr.Android
Create a .NET MAUI project
Open Visual Studio and click on "Create a new project". Search for MAUI, select .NET MAUI App and "Next".
Include the IronOCR.Android library
The library can be added in various ways. The easiest is perhaps by using NuGet.
- Inside Visual Studio, right-click on "Dependencies" and select "Manage NuGet Packages ...".
- Select the "Browse" tab and search for "IronOcr.Android".
- Select the "IronOcr.Android" package and click on "Install".
To prevent issues with other platforms, modify the csproj file to only include the package when targeting the Android platform. In order to do so:
- Right-click on the project and select "Edit Project File".
- Create a new ItemGroup element as such:
<ItemGroup Condition="$(TargetFramework.Contains('android')) == true"> </ItemGroup>XML - Move the "IronOcr.Android" PackageReference inside the ItemGroup we just created.
The above steps will prevent the "IronOcr.Android" package from being used on e.g. iOS platforms (for that purpose, install IronOcr.iOS instead).
Edit "MainActivity.cs"
- Open the "MainActivity.cs" file by navigating to Platforms -> Android.
- Add the
MainActivitymethod and invoke theInitializemethod.
namespace MAUIIronOCRAndroidSample
{
[Activity(Theme = "@style/Maui.SplashTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation | ConfigChanges.UiMode | ConfigChanges.ScreenLayout | ConfigChanges.SmallestScreenSize | ConfigChanges.Density)]
public class MainActivity : MauiAppCompatActivity
{
public MainActivity()
{
IronTesseract.Initialize(this);
}
}
}namespace MAUIIronOCRAndroidSample
{
[Activity(Theme = "@style/Maui.SplashTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation | ConfigChanges.UiMode | ConfigChanges.ScreenLayout | ConfigChanges.SmallestScreenSize | ConfigChanges.Density)]
public class MainActivity : MauiAppCompatActivity
{
public MainActivity()
{
IronTesseract.Initialize(this);
}
}
}Namespace MAUIIronOCRAndroidSample
<Activity(Theme := "@style/Maui.SplashTheme", MainLauncher := True, ConfigurationChanges := ConfigChanges.ScreenSize Or ConfigChanges.Orientation Or ConfigChanges.UiMode Or ConfigChanges.ScreenLayout Or ConfigChanges.SmallestScreenSize Or ConfigChanges.Density)>
Public Class MainActivity
Inherits MauiAppCompatActivity
Public Sub New()
IronTesseract.Initialize(Me)
End Sub
End Class
End NamespaceEdit "MainPage.xaml"
Edit the XAML file to display a button and a label to show the OCR result. For example:
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="MAUIIronOCRAndroidSample.MainPage">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Button
Text="Import File"
Clicked="ReadFileOnImport"
Grid.Row="0"
HorizontalOptions="Center"
Margin="20, 20, 20, 10"/>
<ScrollView
Grid.Row="1"
BackgroundColor="LightGray"
Padding="10"
Margin="10, 10, 10, 30">
<Label x:Name="OutputText"/>
</ScrollView>
</Grid>
</ContentPage>Edit "MainPage.xaml.cs"
First, create an instance of the IronTesseract object. Ensure that IronTesseract is initialized once within a class, as demonstrated in the code below. Instantiating it within a method can be ineffective and may cause unexpected errors.
Next, use the FilePicker.PickAsync method to select a file, then open a reading stream from the FileResult. Create a new OcrInput object and load the image into it. Perform OCR on the image using the tesseract instance and retrieve the text. Finally, display the resulting text in a label.
Please note, the current implementation only supports image files. The package does not yet support PDF documents. Therefore, any PDF-related configurations are deactivated by default and should remain so.
using IronOcr;
namespace MAUIIronOCRAndroidSample;
public partial class MainPage : ContentPage
{
// Initialize IronTesseract once in a class
private IronTesseract ocrTesseract = new IronTesseract();
public MainPage()
{
InitializeComponent();
// Apply License key
IronOcr.License.LicenseKey = "IRONOCR.MYLICENSE.KEY.1EF01";
}
private async void ReadFileOnImport(object sender, EventArgs e)
{
try
{
var options = new PickOptions
{
PickerTitle = "Please select a file"
};
var result = await FilePicker.PickAsync(options);
if (result != null)
{
using var stream = await result.OpenReadAsync();
// Instantiate OcrInput
using var ocrInput = new OcrInput();
// Load image stream
ocrInput.LoadImage(stream);
// Perform OCR
var ocrResult = ocrTesseract.Read(ocrInput);
OutputText.Text = ocrResult.Text;
}
}
catch (Exception ex)
{
// Handle exceptions
System.Diagnostics.Debug.WriteLine(ex);
}
}
}using IronOcr;
namespace MAUIIronOCRAndroidSample;
public partial class MainPage : ContentPage
{
// Initialize IronTesseract once in a class
private IronTesseract ocrTesseract = new IronTesseract();
public MainPage()
{
InitializeComponent();
// Apply License key
IronOcr.License.LicenseKey = "IRONOCR.MYLICENSE.KEY.1EF01";
}
private async void ReadFileOnImport(object sender, EventArgs e)
{
try
{
var options = new PickOptions
{
PickerTitle = "Please select a file"
};
var result = await FilePicker.PickAsync(options);
if (result != null)
{
using var stream = await result.OpenReadAsync();
// Instantiate OcrInput
using var ocrInput = new OcrInput();
// Load image stream
ocrInput.LoadImage(stream);
// Perform OCR
var ocrResult = ocrTesseract.Read(ocrInput);
OutputText.Text = ocrResult.Text;
}
}
catch (Exception ex)
{
// Handle exceptions
System.Diagnostics.Debug.WriteLine(ex);
}
}
}Imports IronOcr
Namespace MAUIIronOCRAndroidSample
Partial Public Class MainPage
Inherits ContentPage
' Initialize IronTesseract once in a class
Private ocrTesseract As New IronTesseract()
Public Sub New()
InitializeComponent()
' Apply License key
IronOcr.License.LicenseKey = "IRONOCR.MYLICENSE.KEY.1EF01"
End Sub
Private Async Sub ReadFileOnImport(ByVal sender As Object, ByVal e As EventArgs)
Try
Dim options = New PickOptions With {.PickerTitle = "Please select a file"}
Dim result = Await FilePicker.PickAsync(options)
If result IsNot Nothing Then
Dim stream = Await result.OpenReadAsync()
' Instantiate OcrInput
Dim ocrInput As New OcrInput()
' Load image stream
ocrInput.LoadImage(stream)
' Perform OCR
Dim ocrResult = ocrTesseract.Read(ocrInput)
OutputText.Text = ocrResult.Text
End If
Catch ex As Exception
' Handle exceptions
System.Diagnostics.Debug.WriteLine(ex)
End Try
End Sub
End Class
End NamespaceLastly, in the .csproj file, make sure that you are only building the project for Android. Since the package we added is only for Android, building the project for all platforms will fail.
Run the Project
This will show you how to run the project and perform OCR.
Download .NET MAUI App Project
You can download the complete code for this guide. It comes as a zipped file that you can open in Visual Studio as a .NET MAUI App project.
Click here to download the project.
Using IronOcr.Android in Avalonia
Similar to MAUI, IronOcr.Android can be used in an Avalonia project with the same setup as described above.
If you want to perform OCR on iOS, navigate to the following article to learn more: "How to Perform OCR on iOS in .NET MAUI"
