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Xamarin / Guides

Customize default annotation tool style in Xamarin

This tutorial only applies to Xamarin.Android. See Xamarin.iOS equivalent here .


When creating a new annotation, the initial properties (such as line thickness, fill color, opacity, etc.) are set to the last value that the user selected for an annotation of that type. For example, if the user changes an ellipse annotation's stroke color from green to red, the next ellipse annotation that the user creates would have a stroke color of red. These default properties are saved in the app's SharedPreferences.

These default properties can be changed programmatically and will take effect the next time when the annotation is created.

For example, to change style properties of a rectangle:

var tool = (RectCreate) toolManager.createTool(ToolManager.ToolMode.RectCreate, null);
    ToolStyleConfig.Instance.GetCustomOpacity(pdfViewCtrl.Context, (int)Annot.Type.e_Square, ""),
    ToolStyleConfig.Instance.GetCustomThickness(pdfViewCtrl.Context, (int)Annot.Type.e_Square, ""),
    null, null

where toolManager is an instance of ToolManager.

A table for annotation type and tool mode mapping can be found here: annotation and its creation tool.

XML attributes

Each annotation has a default style that is defined by its creation tool. For example, when you create a Square annotation using the tool for the first time, the default behavior to draw a rectangle with a red border and a transparent fill color. These default colors can changed through XML attributes.

However the effect will only take place when the app is first loaded.

Set a tool's default style

  1. Add a style to your styles.xml file. For details on supported style attributes, see Tool Style Attributes.

    <style name="ShapeProperty">
        <!-- border color -->
        <item name="annot_color">@android:color/white</item>
        <!-- fill color -->
        <item name="annot_fill_color">@android:color/white</item>
        <!-- thickness -->
        <item name="annot_thickness">1.0</item>
        <!-- opacity -->
        <item name="annot_opacity">1.0</item>
  2. Add the style resource to ToolStyleConfig by calling AddDefaultStyleMap(Int32, Int32).

    The first parameter of addDefaultStyleMap is an annotation type. You can determine the annotation type from the creator tool by referring to the Table of annotations and its creation tool.
    // Add the to RectCreate tool.
    // Since the RectCreate tool creates a Square annotation, the annotation type of a Square
    // annotation is Annot.e_Square
    ToolStyleConfig.Instance.AddDefaultStyleMap((int) Annot.Type.e_Square, Resource.Style.ShapeProperty);

Tool style attributes

####annot_color Annotation color. For annotations that have an annot_fill_color, it represents stroke color.

format: color

####annot_text_color Annotation text color. Used for FreeText annotations.

format: color


Annotation fill color. Used for annotations that have fill colors, including Square, Circle, and FreeText.

format: color


Annotation font size. Used for FreeText annotations.

format: float


Represents a FreeText annotation's maximum font size.

format: float


Represents a FreeText annotation's minimum font size.

format: float


Annotation thickness for border style

format: float


Annotation maximum thickness

format: float


Annotation minimum thickness

format: float


Annotation font. Used for FreeText annotations.

format: string


Annotation opacity

format: float


Annotation icon. Used for Text annotations.

format: string

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