Handwritten signatures in Xamarin Pdf Viewer (SfPdfViewer)

17 Aug 202113 minutes to read

Xamarin PDF Viewer allows you to include handwritten signatures in PDF documents and provides options to modify or remove the existing ones.

Enabling handwritten signature mode

Set the AnnotationMode property of the PDF viewer instance to HandwrittenSignature. After setting the signature mode the signature pad would appear on which the signature can be drawn. After drawing the signature, the Done button should be tapped to add the drawn signature to the PDF, you can use clear button to redraw the signature or close button to cancel signing.

xaml
c#
<syncfusion:SfPdfViewer x:Name="pdfViewer"/>
<Button x:Name="signatureButton" Command="{Binding AnnotationModeCommand, Source={x:Reference Name=pdfViewer}}" CommandParameter="HandwrittenSignature" />
pdfViewer.AnnotationMode = AnnotationMode.HandwrittenSignature;

Disabling handwritten signature mode

Setting the AnnotationMode to None will disable the signature mode and would hide the signature pad.

xaml
c#
<syncfusion:SfPdfViewer x:Name="pdfViewer"/>
<Button x:Name="resetAnnotationButton" Command="{Binding AnnotationModeCommand, Source={x:Reference Name=pdfViewer}}" CommandParameter="None" />
pdfViewer.AnnotationMode = AnnotationMode.None;

Adding Handwritten signature programmatically

By AddHandwrittenSignature or AddAnnotation method, You can add the handwritten signatures programmatically. The created handwritten signature object passed as a parameter. The HandwrittenSignature instance acquires the HandwrittenSignature.InkPointsCollection, page number and position as the parameters.

The HandwrittenSignature.InkPointsCollection is of type List<List<float>>. Each List<float> in this collection represent each stroke of the signature. There will be as many List<float> instances in the InkPointsCollection as the number of strokes in the handwritten signature.

The List<float>, in turn, has the series of alternate X and Y coordinates of the ink stroke. i.e. the values at the odd position are X coordinates and at the even position are Y coordinates.

The following code sample explains adding a single stroke handwritten signature programmatically.

c#
var inkPointsCollection = new List<List<float>>();

inkPointsCollection.Add(new List<float> { 53f, 525f, 53f, 527f, 53f, 528f, 53f, 531f, 53f, 549f, 54f, 570f, 56f, 597f, 57f, 623f, 59f, 652f, 60f, 679f, 62f, 705f, 64f, 726f, 65f, 744f, 66f, 758f, 66f, 768f, 65f, 777f, 65f, 782f, 65f, 784f, 64f, 786f, 64f, 786f, 63f, 786f, 63f, 786f, 63f, 784f, 66f, 774f, 71f, 757f, 79f, 734f, 88f, 708f, 99f, 681f, 112f, 652f, 126f, 627f, 140f, 606f, 150f, 591f, 158f, 582f, 162f, 578f, 164f, 577f, 165f, 576f, 166f, 576f, 165f, 578f, 155f, 592f, 143f, 605f, 121f, 621f, 99f, 631f, 77f, 639f, 54f, 644f, 35f, 645f, 20f, 644f, 10f, 642f, 4f, 642f, 2f, 641f, 1f, 640f, 0f, 639f, 0f, 639f, 2f, 639f, 20f, 645f, 47f, 657f, 75f, 672f, 106f, 688f, 137f, 704f, 168f, 718f, 197f, 732f, 221f, 741f, 240f, 748f, 254f, 753f, 254f, 753f });

System.Drawing.Point position = new System.Drawing.Point(100, 100);
HandwrittenSignature signature = new HandwrittenSignature(inkPointsCollection, 1, position);
signature.Settings.Color = Color.Red;    

//Method 1: Adds the handwritten signature using `AddHandwrittenSignature` method
pdfViewerControl.AddHandWrittenSiganture(signature);       

//Method 2: Adds the handwritten signature using `AddAnnotation` method
//pdfViewerControl.AddAnnotation(signature);

Adding handwritten signature on the specified page

The AddHandwrittenSignature(handwrittenSignature, pageNumber) API adds the given handwritten signature on the page specified by the pageNumber argument. When this API is used, the handwritten signature is added at the center of the page.

c#
pdfViewer.AddHandwrittenSignature(handwrittenSignature, 2);

NOTE

The pageNumber argument in the API is optional. If it is not specified, the signature is added to the current page.

Adding handwritten signature on the specified page and position

The AddHandwrittenSignature(handwrittenSignature, position, pageNumber) API adds the handwritten signature on the page specified by the pageNumber argument and the position specified by the position argument.

c#
System.Drawing.Point  position = new System.Drawing.Point(200,200);
pdfViewer.AddHandwrittenSignature(handwrittenSignature, position, 2);

NOTE

The pageNumber argument in the API is optional. If it is not specified, the signature is added in the current page.

Adding handwritten signature on multiple pages and multiple positions

The AddHandwrittenSignature(handwrittenSignature, pageAndPositionCollection) API can be used to add the same handwritten signature instance to the multiple positions in multiple pages. The positionCollection argument is of type Dictionary whose keys correspond to the page numbers and the values correspond to the list of positions within each page that the signature has to be added.

c#
List<System.Drawing.Point> pointCollection1 = new List<System.Drawing.Point>();
List<System.Drawing.Point> pointCollection2 = new List<System.Drawing.Point>();
Dictionary<int, List<System.Drawing.Point>> pageAndPositionCollection = new Dictionary<int, List<System.Drawing.Point>>();
System.Drawing.Point position1 = new System.Drawing.Point(20, 200);
System.Drawing.Point position2 = new System.Drawing.Point(200, 20);
System.Drawing.Point position3 = new System.Drawing.Point(400, 40);
System.Drawing.Point position4 = new System.Drawing.Point(40, 400);
pointCollection1.Add(position1);
pointCollection1.Add(position2);
pointCollection2.Add(position3);
pointCollection2.Add(position4);
pageAndPositionCollection.Add(1, pointCollection1);
pageAndPositionCollection.Add(3, pointCollection2);
pdfViewerControl.AddHandWrittenSignature(handwrittenSignature, pageAndPositionCollection);

Select handwritten signature programmatically

By SelectAnnotation method, You can select the handwritten signature programmatically. The specified handwritten signature object passed as a parameter.

The following code sample illustrates the same.

c#
//Selects the specified handwritten signature 
pdfViewer.SelectAnnotation(signature);

NOTE

Once SelectAnnotation method is called and as long as the annotation stays selected, the SelectedAnnotation property will return the same instance as the parameter of this method.

Deselect handwritten signature programmatically

By DeselectAnnotation method, You can deselect the handwritten signature programmatically .The specified handwritten signature object passed as a parameter.

The following code sample illustrates the same.

c#
//Deselects the specified handwritten signature
pdfViewer.DeselectAnnotation(signature);

NOTE

There is no effect in calling DeselectAnnotation method, if the given annotation is not selected. Once this method is called, the SelectedAnnotation property will return null until any other annotation gets selected.

Customizing the position of handwritten signature drawn using the built-in signature pad

By default, when the “Done” button of the signature pad is tapped, the signature is added at the center of the current page. But the page number and position that the signature is added can be customized using the AddHandwrittenSignature API discussed above.
When the “Done” button is tapped, the InkAdded event is raised. The handwritten signature instance that is drawn on the signature pad is exposed as the sender argument of the InkAdded event. The signature instance can then be added at any page or position using any of the required AddHandwrittenSignature overloads.

c#
pdfViewer.InkAdded += pdfViewer_InkAdded;

private void pdfViewer_InkAdded(object sender, InkAddedEventArgs args)
{
     HandwrittenSignature handwrittenSignature = sender as HandwrittenSignature;
     System.Drawing.Point  position = new System.Drawing.Point(200,200);
pdfViewer.AddHandwrittenSignature(handwrittenSignature, position, 2);

}

Customizing the appearance of handwritten signatures

You can customize the default values such as stroke color, opacity, and thickness of all signatures to be added. This will not affect the already added signatures.

Setting the default stroke color

You can set the default stroke color of handwritten signatures by using the SfPdfViewer.AnnotationSettings.HandwrittenSignature.Color property. Refer to the following code.

c#
pdfViewer.AnnotationSettings.HandwrittenSignature.Color = Color.Red;

Setting the default opacity

You can set the default opacity of handwritten signatures by using the SfPdfViewer.AnnotationSettings.HandwrittenSignature.Opacity property. Opacity value ranges from 0 to 1. Refer to the following code example.

c#
pdfViewer.AnnotationSettings.HandwrittenSignature.Opacity = 0.5f;

Setting the default thickness

You can set the thickness of handwritten signatures by using the SfPdfViewer.AnnotationSettings.HandwrittenSignature.Thickness property. Refer to the following code example.

c#
pdfViewer.AnnotationSettings.HandwrittenSignature.Thickness = 5;

Setting the default minimum size

By the SfPdfViewer.AnnotationSettings.HandwrittenSignature.MinimumSize property, You can set the minimum size to which the handwritten signatures could be resized.

Refer the following code example:

c#
//Sets the minimum size for the handwritten signatures
pdfViewer.AnnotationSettings.HandwrittenSignature.MinimumSize = new Size(10, 10);

Similarity with Ink annotations

The handwritten signatures are preserved as ink annotations in PdfViewer. However, on saving you can choose whether to preserve the signature as ink annotation or flatten it. This can be achieved using the pdfViewer.AnnotationSettings.HandwrittenSignature.FlattenSignatureOnSave property.

c#
pdfViewer.AnnotationSettings.HandwrittenSignature.FlattenSignatureOnSave = true;

NOTE

The default value of the property is true.

Events

Since the handwritten signature is preserved as ink annotation, the events for both handwritten signatures and ink annotations are same. The events supported by ink annotations are described in detail here.

When the common events occur, ink annotation and handwritten signature can be distinguished using the event argument’s IsChildSignature property. Also, the sender parameter will be of type InkAnnotation and HandwrittenSignature for the respective annotations. For brevity, only the InkSelected event is illustrated below.

c#
pdfViewer.InkSelected += PdfViewer_InkSelected;

private void PdfViewer_InkSelected(object sender, Syncfusion.SfPdfViewer.XForms.InkSelectedEventArgs args)
{
	if(args.IsSignature)
	{
		//The event occurred was raised by handwritten signature
		//The "sender" parameter is of type "HandwrittenSignature"
	}
	else
	{
		//The event occurred was raised by ink annotation
		//The "sender" parameter is of type "InkAnnotation"
	}
}

How to enable or disable handwritten signature interaction?

The interaction operation can be enabled or disabled for handwritten signature alone by setting the IsLocked API to false or true respectively.

For example, the following code disables the interaction operations for all handwritten signatures in the PDF. But other annotation types can be selected, moved, resized, or removed.

c#
//Disable the handwritten signature annotation interaction
pdfViewerControl.AnnotationSettings.HandwrittenSignature.IsLocked = true;

The interaction with handwritten signatures will be allowed only if the SfPdfViewer.AnnotationSettings.IsLocked API is set to false. The following code does not allow the interactions with handwritten signatures, although the IsLocked property of the handwritten signature is set to false.

c#
//Disables the handwritten signature interaction, though its 'IsLocked' property is set to ‘false’ 
pdfViewerControl.AnnotationSettings.IsLocked = true;
pdfViewerControl.AnnotationSettings.HandwrittenSignature.IsLocked = false;

How to get and set the name of the handwritten signatures?

The PDF Viewer allows the users to get and set the name of handwritten signatures through the Name API.

The following code sample explains modifying the name of the handwritten signature in the InkAdded event.

c#
private void PdfViewerControl_InkAdded(object sender, InkAddedEventArgs args)
{
   if(sender is HandwrittenSignature)
    {
     (sender as HandwrittenSignature).Name = "HandwrittenSignature1";
    }
}

NOTE

For illustration purposes, we have only provided the sample for modifying the name of the handwritten signature in the InkAdded event. But this can be done in all other events as well.

NOTE

You can also explore our Xamarin.Forms PDF Viewer example to knows the functionalities of each feature.