ArcGIS Pro 3.4 API Reference Guide
ArcGIS.Desktop.Core.Geoprocessing Namespace / Geoprocessing Class / ShowMessageBox Method
Pass messages from the result (IGPResult) of ExecuteToolAsync to be shown on the message box.
Header of the messages.
Geoprocessing message box style, for example, GPMessageBoxStyle.Default or GPMessageBoxStyle.Error
Title at the top bar of the message box.
Path to a icon image to be shown next to content header.
Example Version

ShowMessageBox Method
Shows a messag box with Geoprocessing messages as formatted for the message box.
Syntax

Parameters

messages
Pass messages from the result (IGPResult) of ExecuteToolAsync to be shown on the message box.
content_header
Header of the messages.
style
Geoprocessing message box style, for example, GPMessageBoxStyle.Default or GPMessageBoxStyle.Error
window_title
Title at the top bar of the message box.
icon_source
Path to a icon image to be shown next to content header.
parentViewModel
Example
FieldMappings
var environment = Geoprocessing.MakeEnvironmentArray(overwriteoutput: true);

var prj = Project.Current;
var map = MapView.Active;

var defaultGDB = Project.Current.DefaultGeodatabasePath;

var featLayers = map.Map.Layers.OfType<FeatureLayer>();

var targetLayer = featLayers.ElementAt(0);  // First layer in TOC
var joinLayer = featLayers.ElementAt(1);    // Second layer in TOC

var outputFeatureClass = @"C:/temp/outputFC3.shp";

// Specify the field map in Spatial Join with target and join feature class/layers in the App
// Run Spatial Join manually - then Copy the fieldmap string from the result in Geoprocessing history and paste it for the fieldmap parameter. 
// in this example of fieldmap, FireStations is the name of join layer
// FireStations layer has two numeric fileds (used in Fieldmap): TYPE and NUMBER - these two fields are used in the FiedlMap
//
var joinLayerName = joinLayer.Name;
var fieldMap = "TYPE 'TYPE' true true false 4 Long 0 0,Count,#,{joinLayerName},TYPE,-1,-1;NUMBER 'NUMBER' true true false 4 Long 0 0,Max,#,{joinLayerName},NUMBER,-1,-1";

var toolParameters = Geoprocessing.MakeValueArray(targetLayer, joinLayer, outputFeatureClass, "JOIN_ONE_TO_ONE", "KEEP_COMMON", fieldMap, "INTERSECT");

GPExecuteToolFlags executeFlags = GPExecuteToolFlags.AddOutputsToMap | GPExecuteToolFlags.GPThread | GPExecuteToolFlags.AddToHistory | GPExecuteToolFlags.RefreshProjectItems;

IGPResult gpResult = await Geoprocessing.ExecuteToolAsync("analysis.SpatialJoin", toolParameters, environment, null, null, executeFlags);

Geoprocessing.ShowMessageBox(gpResult.Messages, "GP Messages", gpResult.IsFailed ? GPMessageBoxStyle.Error : GPMessageBoxStyle.Default);
Setting environments, MakeEnvironmentArray
// get the syntax of the tool from Python window or from tool help page
string in_features = @"C:\data\data.gdb\HighwaysWeb84";
string out_features = @"C:\data\data.gdb\HighwaysUTM";
var param_values = Geoprocessing.MakeValueArray(in_features, out_features);

// crate the spatial reference object to pass as an argument to management.CopyFeatures tool
var sp_ref = await QueuedTask.Run(() =>
{
  return SpatialReferenceBuilder.CreateSpatialReference(26911);    // UTM 83 11N: 26911
});

// set output coordinate system environment           
var environments = Geoprocessing.MakeEnvironmentArray(outputCoordinateSystem: sp_ref);
// set environments in the 3rd parameter
var gp_result = await Geoprocessing.ExecuteToolAsync("management.CopyFeatures", param_values, environments, null, null, GPExecuteToolFlags.AddOutputsToMap);

Geoprocessing.ShowMessageBox(gp_result.Messages, "Contents", GPMessageBoxStyle.Default, "Window Title");

//return gp_result;
Geoprocessing specialized MessageBox
var gp_result = await Geoprocessing.ExecuteToolAsync("management.GetCount", Geoprocessing.MakeValueArray(@"C:\data\f.gdb\hello"));
// this icon shows up left of content_header
string icon_src = @"C:\data\Icons\ModifyLink32.png";
Geoprocessing.ShowMessageBox(gp_result.Messages, "Content Header", GPMessageBoxStyle.Error, "Window Title", icon_src);
How to pass parameter with multiple or complex input values
var environments = Geoprocessing.MakeEnvironmentArray(overwriteoutput: true);

string toolName = "Snap_edit";  // or use edit.Snap

// Snap tool takes multiple inputs each of which has
// Three (3) parts: a feature class or layer, a string value and a distance
// Each part is separated by a semicolon - you can get example of sytax from the tool documentation page
var snapEnv = @"'C:/SnapProject/fgdb.gdb/line_1' END '2 Meters';'C:/SnapProject/fgdb.gdb/points_1' VERTEX '1 Meters';'C:/SnapProject/fgdb.gdb/otherline_1' END '20 Meters'";

var infc = @"C:/SnapProject/fgdb.gdb/poly_1";

var snapParams = Geoprocessing.MakeValueArray(infc, snapEnv);

GPExecuteToolFlags tokens = GPExecuteToolFlags.RefreshProjectItems | GPExecuteToolFlags.GPThread | GPExecuteToolFlags.AddToHistory;

IGPResult snapResult = await Geoprocessing.ExecuteToolAsync(toolName, parameters, environments, null, null, tokens);

//return gpResult;
How to use Geoprocessing public event
ArcGIS.Desktop.Core.Events.GPExecuteToolEvent.Subscribe(e =>
      {
        string id = e.ID;                   // Same as history ID
        if (e.IsStarting == false)  // Execute completed
          _ = e.GPResult.ReturnValue;
        System.Windows.MessageBox.Show("event triggered.");
      });
await Geoprocessing.ExecuteToolAsync("management.GetCount", Geoprocessing.MakeValueArray(@"c:\shape_file.shp"));
Requirements

Target Platforms: Windows 11, Windows 10

ArcGIS Pro version: 3 or higher.
See Also