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Creating enumerations

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There are cases where Java Android libraries use integer constants to represent states that are passed to properties or methods of the libraries. For widely distributed bindings, it may useful to bind these integer constants to enums in C# to provide a nicer API for consumers.

For internal or low usage bindings it's usually not worth the effort to set these up, as the consumers can simply use the bound constants instead of an enumeration.

To facilitate this mapping, two files are added to binding projects by the default project template:

  • EnumFields.xml - This file defines the mapping between Java integer constants and a C# enumeration

  • EnumMethods.xml - This file defines which methods/properties that currently take an int method parameter or have an int return type should be modified to use an enumeration instead.

Defining an enum using EnumFields.xml

The EnumFields.xml file contains the mapping between Java int constants and C# enums. Let's take the following example of a C# enum being created for a set of int constants:

<mapping jni-class="com/skobbler/ngx/map/realreach/SKRealReachSettings" clr-enum-type="Skobbler.Ngx.Map.RealReach.SKMeasurementUnit">
    <field jni-name="UNIT_SECOND" clr-name="Second" value="0" />
    <field jni-name="UNIT_METER" clr-name="Meter" value="1" />
    <field jni-name="UNIT_MILIWATT_HOURS" clr-name="MilliwattHour" value="2" />
</mapping>

Here we have taken the Java class SKRealReachSettings and defined a C# enum called SKMeasurementUnit in the namespace Skobbler.Ngx.Map.RealReach. The field entries defines the name of the Java constant (example UNIT_SECOND), the name of the enum entry (example Second), and the integer value represented by both entities (example 0).

Defining getter/setter methods using EnumMethods.xml

The EnumMethods.xml file allows changing method parameters and return types from Java int constants to C# enums. In other words, it maps the reading and writing of C# enums (defined in the EnumFields.xml file) to Java int constant get and set methods.

Given the SKRealReachSettings enum defined above, the following EnumMethods.xml file would define the getter/setter for this enum:

<mapping jni-class="com/skobbler/ngx/map/realreach/SKRealReachSettings">
    <method jni-name="getMeasurementUnit" parameter="return" clr-enum-type="Skobbler.Ngx.Map.RealReach.SKMeasurementUnit" />
    <method jni-name="setMeasurementUnit" parameter="measurementUnit" clr-enum-type="Skobbler.Ngx.Map.RealReach.SKMeasurementUnit" />
</mapping>

The first method line maps the return value of the Java getMeasurementUnit method to the SKMeasurementUnit enum. The second method line maps the first parameter of the setMeasurementUnit to the same enum.

With all of these changes in place, you can use the follow code in .NET for Android to set the MeasurementUnit:

realReachSettings.MeasurementUnit = SKMeasurementUnit.Second;