ArcGIS Pro 2.7 API Reference Guide
OnToolMouseDown Method
Example 

ArcGIS.Desktop.Mapping Namespace > MapTool Class : OnToolMouseDown Method
A MapViewMouseButtonEventArgs that contains the event data.
Occurs when a mouse button is pressed on the view.
Syntax
protected virtual void OnToolMouseDown( 
   MapViewMouseButtonEventArgs e
)
Protected Overridable Sub OnToolMouseDown( _
   ByVal e As MapViewMouseButtonEventArgs _
) 

Parameters

e
A MapViewMouseButtonEventArgs that contains the event data.
Remarks
This method is intended to perform synchronous operations associated with a mouse down event. To perform any asynchronous operations set the handled property on the MapViewMouseButtonEventArgs to true and override the HandleMouseDownAsync virtual method.
Example
Create a tool that allows you to click in the view and return the point in map coordinates that was clicked.
/*

   Copyright 2018 Esri

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

   See the License for the specific language governing permissions and
   limitations under the License.

*/
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using ArcGIS.Desktop.Mapping;
using ArcGIS.Desktop.Framework.Threading.Tasks;

namespace Examples
{
  internal class GetMapCoordinates : MapTool
  {
    protected override void OnToolMouseDown(MapViewMouseButtonEventArgs  e)
    {
      if (e.ChangedButton == System.Windows.Input.MouseButton.Left)
        e.Handled = true; //Handle the event args to get the call to the corresponding async method
    }

    protected override Task HandleMouseDownAsync(MapViewMouseButtonEventArgs e)
    {
      return QueuedTask.Run(() =>
      {
        //Convert the clicked point in client coordinates to the corresponding map coordinates.
        var mapPoint = MapView.Active.ClientToMap(e.ClientPoint);
        ArcGIS.Desktop.Framework.Dialogs.MessageBox.Show(string.Format("X: {0} Y: {1} Z: {2}",
                       mapPoint.X, mapPoint.Y, mapPoint.Z), "Map Coordinates");
      });
    }
  }
}
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

MapTool Class
MapTool Members