Always getting error-“Object reference not set to an instance of an object.”

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I tried this way...so that when i click any menuitem in button1 it will check and check the same menuitem in the second button...but some where am getting error...I want to write it in better way .so that it will work as i need with out any issuse.here is the below code i did so far...how can i solve this issue as well as how can i improve this coding... here is my code..

HTML

<grid>
    <grid.rowdefinitions>
        <rowdefinition height="50" />
        <rowdefinition height="50" />
        <rowdefinition height="50" />
        <rowdefinition height="50" />
    </grid.rowdefinitions>
    <stackpanel grid.row="0" orientation="Horizontal" flowdirection="LeftToRight">
        <Button  Name="btnPhone" Content="Business"   Click="OnbtnPhoneClick" ></Button>

        <Button Name="ddBtnPhone" Width="25"  Click="OnddBtnPhoneClick" Height="47">
            <Button.Content>
                <path x:name="btnArrow1" margin="4" verticalalignment="Center" width="10" fill="#FF527DB5" stretch="Uniform" horizontalalignment="Right" data="F1 M 301.14,-189.041L 311.57,-189.041L 306.355,-182.942L 301.14,-189.041 Z " xmlns:x="#unknown" />
            </Button.Content>
            <Button.ContextMenu>
                <contextmenu x:name="cmPhone" xmlns:x="#unknown">
                    <menuitem header="Assistant " name="mnIAssistant" checked="OnMenuItemChecked" click="OnMenuItemClick" />                                                    <menuitem header="Business" name="mnIBusiness" checked="OnMenuItemChecked" click="OnMenuItemClick" />                                                    <menuitem header="Business 2 " name="mnIBusiness2" checked="OnMenuItemChecked" click="OnMenuItemClick" />
                    <menuitem header="Business FAX " name="mnIBusinessFAX" checked="OnMenuItemChecked" click="OnMenuItemClick" />
                    <menuitem header="Call Back" name="mnICallback" checked="OnMenuItemChecked" click="OnMenuItemClick" />
                    <menuitem header="Car" name="mnICar" click="OnMenuItemChecked" />

                </contextmenu>
            </Button.ContextMenu>
        </Button>
        <textbox height="19" name="textBox1" width="120" />
    </stackpanel>
    <stackpanel grid.row="2" orientation="Horizontal" flowdirection="LeftToRight">
        <Button  Name="btnHome" Content="Home" Click="OnbtnHomeClick"  Height="26" Width="64" />

        <Button Name="ddBtnHome" Width="25"  Click="OnddBtnHomeClick" Margin="0,0,0,5"  >
            <Button.Content>
                <path x:name="btnArrow2" margin="4" verticalalignment="Center" width="10" fill="#FF527DB5" stretch="Uniform" horizontalalignment="Right" data="F1 M 301.14,-189.041L 311.57,-189.041L 306.355,-182.942L 301.14,-189.041 Z " xmlns:x="#unknown" />
            </Button.Content>
            <Button.ContextMenu>
                <contextmenu name="cmHome">
                    <menuitem header="Assistant " name="mnIAssistant1" checked="OnMenuItemChecked" click="OnMenuItemClick" />
                    <menuitem header="Business" name="mnIBusiness1" checked="OnMenuItemChecked" click="OnMenuItemClick" />
                    <menuitem header="Business 2 " name="mnIBusiness21" checked="OnMenuItemChecked" click="OnMenuItemClick" />
                    <menuitem header="Business FAX " name="mnIBusinessFAX1" checked="OnMenuItemChecked" click="OnMenuItemClick" />
                    <menuitem header="Call Back" name="mnICallback1" checked="OnMenuItemChecked" click="OnMenuItemClick" />
                    <menuitem header="Car" name="mnICar1" click="OnMenuItemChecked" />

                </contextmenu>
            </Button.ContextMenu>
        </Button>
        <textbox height="23" name="textBox2" width="120" />
    </stackpanel>

    <border grid.row="3" borderthickness="2" borderbrush="Blue">
        <textblock name="tbWebpage" grid.row="3" removed="White" verticalalignment="Top" height="20">
                                    <hyperlink navigateuri="tbWebpage.Text" requestnavigate="Hyperlink_RequestNavigate"></hyperlink>
                                </textblock>
    </border>
</grid>

C#

namespace MenuItemsChecked
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        //string[] arrMenitems = { "business", "a1", "a2", "a3","a4" };
        Button btnCommon = new Button();
        TextBox txtCommon = new TextBox();
        MenuItem mnItem;
        public MainWindow()
        {
            InitializeComponent();
        }

        private void AddMenuItems(ContextMenu cMenu, Button btnName, TextBox txtBoxName)
        {
           //mnItem.Items.Add(arrMenitems);
            if (cMenu.Items.Count != 0)
            {
                //mnItem = new MenuItem();
                //mnItem.Header = "Business";
                //mnItem.IsCheckable = true;
                //cMenu.Items.Add(mnItem);
                //mnItem = new MenuItem();
                //mnItem.Header = "Assistant";
                //mnItem.IsCheckable = true;
                //cMenu.Items.Add(mnItem);
                //mnItem = new MenuItem();
                //mnItem.Header = "Business 2";
                //mnItem.IsCheckable = true;
                //cMenu.Items.Add(mnItem);
                //mnItem = new MenuItem();
                //mnItem.Header = "Business FAX";
                //mnItem.IsCheckable = true;
                //cMenu.Items.Add(mnItem);
                //mnItem = new MenuItem();
                //mnItem.Header = "Call Back";
                //mnItem.IsCheckable = true;
                //cMenu.Items.Add(mnItem);
                //cMenu.Items.Add(mnItem);
                //cmCommon = cMenu;
                cMenu.AddHandler(MenuItem.ClickEvent, new RoutedEventHandler(OnMenuItemClick));
                cMenu.AddHandler(MenuItem.MouseLeftButtonUpEvent, new MouseButtonEventHandler(OnMouseButtonUpEventClick));
               // cMenu.AddHandler(MenuItem.CheckedEvent, new RoutedEventHandler(OnMenuItemChecked));
                btnCommon = btnName;
                //txtCommon = txtBoxName;

            }

        }

        private void OnMenuItemChecked(object sender, RoutedEventArgs e)
        {
            RoutedEventArgs args = e as RoutedEventArgs;
            MenuItem item = args.OriginalSource as MenuItem;
            if (sender == mnIAssistant)
            {
                mnIAssistant.IsChecked = true;
                mnIAssistant1.IsChecked = true;
            }

            if (sender == mnIBusiness)
            {
                mnIBusiness.IsChecked = true;
                mnIBusiness1.IsChecked = true;
            }
            if (sender == mnIBusiness2)
            {
                mnIBusiness2.IsChecked = true;
                mnIBusiness21.IsChecked = true;
            }
            if (sender == mnIBusinessFAX)
            {
                mnIBusinessFAX.IsChecked = true;
                mnIBusinessFAX1.IsChecked = true;
            }
            if (sender == mnICallback)
            {
                mnICallback.IsChecked = true;
                mnICallback1.IsChecked = true;
            }
            if (sender == mnICar)
            {
                mnICar.IsChecked = true;
                mnICar1.IsChecked = true;
            }
            if (sender == mnIAssistant1)
            {
                mnIAssistant.IsChecked = true;
                mnIAssistant1.IsChecked = true;
            }
            if (sender == mnIBusiness1)
            {
                mnIBusiness.IsChecked = true;
                mnIBusiness1.IsChecked = true;
            }
            if (sender == mnIBusiness21)
            {
                mnIBusiness2.IsChecked = true;
                mnIBusiness21.IsChecked = true;
            }
            if (sender == mnIBusinessFAX1)
            {
                mnIBusinessFAX.IsChecked = true;
                mnIBusinessFAX1.IsChecked = true;
            }
            if (sender == mnICallback1)
            {
                mnICallback.IsChecked = true;
                mnICallback1.IsChecked = true;
            }
            if (sender == mnICar1)
            {
                mnICar.IsChecked = true;
                mnICar1.IsChecked = true;
            }



        }
        private void OnMouseButtonUpEventClick(object sender, MouseButtonEventArgs e)
        {
            (sender as MenuItem).IsChecked = !(sender as MenuItem).IsChecked;
            ((sender as MenuItem).Parent as ContextMenu).IsOpen = false;
        }


        private void OnMenuItemClick(object sender, RoutedEventArgs e)
        {
            RoutedEventArgs args = e as RoutedEventArgs;
           // MenuItem item = args.OriginalSource as MenuItem;
            //string header = item.Header.ToString();
            MenuItem menuitem = sender as MenuItem; ///always getting error-"Object reference not set to an instance of an object."
            //ContextMenu cm = sender as ContextMenu;
            string name = menuitem.Name;
            string header = menuitem.Header.ToString();
           if ((sender == mnIBusiness) |(sender == mnIBusiness1))
                {
                    if (header == "Business")
                    {
              
                    mnIBusiness.IsChecked = true;
                    mnIBusiness1.IsChecked = true;
                  }
                btnCommon.Content = header;
                //item.IsCheckable = true;                
                 
            }
            else if ((sender == mnIAssistant) | (sender == mnIAssistant1))
            {
                if (header == "Assistant")
                {
                    mnIAssistant.IsChecked = true;
                    mnIAssistant1.IsChecked = true;
                }
                btnCommon.Content = header;
                ///item.IsChecked = true;
            }
           else if ((sender == mnIBusiness2) | (sender == mnIBusiness21))
            {
               //if(header=="Business 2")
               //{
                 mnIBusiness2.IsChecked = true;
                mnIBusiness21.IsChecked = true;
               //}
                btnCommon.Content = header;
                //item.IsChecked = true;
            }
           else if ((sender == mnIBusinessFAX) |(sender == mnIBusinessFAX1))
            {
               if(header=="Business FAX")
               {
                   mnIBusinessFAX.IsChecked = true;
                   mnIBusinessFAX1.IsChecked = true;
               }
                btnCommon.Content = header;
                //item.IsChecked = true;
            }
           else if ((sender == mnICallback1) | (sender == mnICallback))
           {
               if (header == "Call Back")
               {
                   mnICallback.IsChecked = true;
                   mnICallback1.IsChecked = true;
               }
               btnCommon.Content = header;
               //item.IsChecked = true;
           }
            else 
            {
                if (header == "Car")
                {
                    mnICar.IsChecked = true;
                    mnICar1.IsChecked = true;
                }
                btnCommon.Content = header;
                
            }
          
            txtCommon.Text = string.Empty;
        }

        private void OnddBtnPhoneClick(object sender, RoutedEventArgs e)
        {
            ButtonContextMenuDisplay(sender);
            AddMenuItems(cmPhone, btnPhone, textBox1);
        }

        private void OnddBtnHomeClick(object sender, RoutedEventArgs e)
        {
            ButtonContextMenuDisplay(sender);
            AddMenuItems(cmHome, btnHome, textBox2);
        }

        private void ButtonContextMenuDisplay(object sender)
        {
            (sender as Button).ContextMenu.IsEnabled = true;
            (sender as Button).ContextMenu.PlacementTarget = (sender as Button);
            (sender as Button).ContextMenu.IsOpen = true;
            (sender as Button).ContextMenu.Placement = System.Windows.Controls.Primitives.PlacementMode.Bottom;
        }

      
    }
}

Posted 15-Jul-13 17:10pm

keerth516

Updated 15-Jul-13 17:15pm

v4

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Thanks7872 15-Jul-13 23:59pm

Remove unnecessary code.Only post code block in which you got the error.

1 solution

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Sergey Alexandrovich Kryukov · Accepted Answer · 2013-07-15T18:03:00

It's unlikely that the line where you put the comment "always getting error-"Object reference not set to an instance of an object" is really the line where you exception is really thrown, if the method of this line is really the one added as the handler of the event Click. More likely, your observation is not correct.

Not to worry; you can easily check it up properly and fix the problem. This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferenced by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object"[^].

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx[^],
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx[^].

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx[^].

Good luck,

—SA