unable to deal with hook connection

YashikaSareen

Hi every1,
I am stuck up with a problem.I want to create an application in which on the click event of the tool a form should be displayed which will be having a button.On the click event of this button,it should print the name of the first layer in the arcmap.The problem is the file through which we hook up the application returns null when the click event of button is called.It shows an exception of unreferenced object instance.below is the code.Please rectify whereever wrong.

Tool.cs
using System;
using System.Collections.Generic;
using System.Text;
using ESRI.ArcGIS.ArcMapUI;
using ESRI.ArcGIS.Carto;
using ESRI.ArcGIS.Framework;
using ESRI.ArcGIS.Geometry;
using ESRI.ArcGIS.SystemUI;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using ESRI.ArcGIS.ADF.CATIDs;
using ESRI.ArcGIS.Geodatabase;
using ESRI.ArcGIS.Controls;



namespace Toolforselection
{
    [Guid("cbf31922-bf3c-487d-891f-1661c078e853")]
    [ClassInterface(ClassInterfaceType.None)]
    [ProgId("Toolforselection.Tool")]
    public class Tool : ICommand
    {
        private IHookHelper m_hookHelper = null;
        [System.Runtime.InteropServices.DllImport("gdi32.dll")]
        static extern bool DeleteObject(IntPtr hObject);

        #region "Component Category Registration"
        [ComRegisterFunction()]
        static void Reg(string regKey)
        {
            MxCommands.Register(regKey);
        }

        [ComUnregisterFunction()]
        static void Unreg(string regKey)
        {
            MxCommands.Unregister(regKey);
        }
        #endregion

        public ILayer l1;
        public ILayer l2;
        public IMxApplication mxApplication;  //to create application display object

        IApplication m_application;

        private IntPtr m_hBitmap;
        public IApplication m_app1;
        public IApplication m_app;
        public IMxDocument m_mxDoc;
        public MxDocument m_mxDocument;
        public Map m_map;
        public PageLayout m_pageLayout;
        private System.Windows.Forms.Button button1;
        public IFeatureClass featureClass;
        private bool m_enabled;
       
            #region ICommand Members

        public string Message
        {
            get
            {
                // Set the message string that appears in the statusbar of the
                // application when the mouse passes over the command.
                return "secondtool";
                //return null;
            }

        }
        public int HelpContextID
        {
            get
            {
                return 0;
            }
        }

        public string Name
        {
            get
            {

                return "sample tool";
                //return null;
            }
        }


        public void OnClick()
        {
            Form1 f = new Form1();
            f.Show();
        }
          public int Bitmap
        {
            get
            {
                return m_hBitmap.ToInt32();

            }
        }
        public void OnCreate(object hook)
        {
            m_app = hook as IApplication;
            m_mxDoc = m_app.Document as IMxDocument;
            m_mxDocument = m_app.Document as MxDocument;
            m_map = m_mxDoc.FocusMap as Map;
        //    try
        //    {
        //        m_hookHelper = new HookHelperClass();
        //        m_hookHelper.Hook = hook;
 
        //        if (m_hookHelper.ActiveView == null)
        //            m_hookHelper = null;
        //    }
        //    catch
        //    {
        //        m_hookHelper = null;
        //    }
        //    if (m_hookHelper == null)
        //       m_enabled = false;
        //    else
        //       m_enabled = true;


        }


        public string Caption
        {
            get
            {

                return "ToolForSelection";
                //return null;
            }
        }

        public string Tooltip
        {
            get
            {
                // Set the string that appears in the screen tip.
                return "ToolForSelection";
                //return null;
            }
        }
        public bool Checked
        {
            get
            {
                return false;
            }
        }

        public bool Enabled
        {
            get
            {
                // Add some logic here to specify when the command should
                // be enabled. In this example, the command is always enabled.
                return true;
            }
        }
        public string HelpFile
        {
            get
            {
                return null;
            }
        }

        public string Category
        {
            get
            {
                // Set the category of this command. This determines where the
                // command appears in the Commands panel of the Customize dialog.
                return "test tool";
                //return null;
            }
        }

        #endregion

      

    }
}




Form1.cs                                   //to add form



using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using ESRI.ArcGIS.ArcMapUI;
using ESRI.ArcGIS.Carto;
using ESRI.ArcGIS.Framework;
using ESRI.ArcGIS.Geometry;
using ESRI.ArcGIS.SystemUI;
using System.Runtime.InteropServices;
using ESRI.ArcGIS.ADF.CATIDs;
using ESRI.ArcGIS.Geodatabase;
using ESRI.ArcGIS.Controls;

namespace Toolforselection
{
    public partial class Form1 : Form
    {
       // private IHookHelper hookHelper;
        public ILayer l1;
        public ILayer l2;
        public IMxApplication mxApplication;  //to create application display object
       // IApplication m_application;
        private IntPtr m_hBitmap;
        public IApplication m_app;
        public IMxDocument m_mxDoc;
        public MxDocument m_mxDocument;
        public Map m_map;
        public PageLayout m_pageLayout;
        public IFeatureClass featureClass;


        public Form1()
        {
           // this.hookHelper = hookHelper;
            //MessageBox.Show(m_app.Name);

            InitializeComponent();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void button3_Click(object sender, EventArgs e)
        {
            MessageBox.Show(m_app.Name);
            //MessageBox.Show("abc");

            l1 = m_map.get_Layer(0);              //here m_map has value null(exception)
            MessageBox.Show(l1.Name);
        }
     
   

    }
}

JanDuske

You are creating an instance of your Form class without passing any reference to the calling ArcMap application. You declare member variables in the Form class for the MxDocument and Application, but you never set them (m_map, m_app...). If you had declared the member variables of your form private instead of public (as it would be correct in an object oriented design approach) you would have gotten a compiler warning telling you that those variables never get a value assigned.
You should try to pass the IApplication object as parameter of your Forms constructor, from that object you can derive all the other references you might need. Set the m_app variable to the Application reference you pass to the constructor, and set all other member variables by using the application's attributes (see documentation for IApplication (ArcMap), IMxDocument etc)