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Im working on a c++ windows form application code where i change the color of an image to a different color , The code executes perfectly and form shows but whenever i press the button that supposed to change color it gives me an error saying "NullreferenceExecution was unhandled" "Object reference not set to an instance of object"

I really need help!
my code:

C++
 #pragma once


namespace AmAma {

	using namespace System;
	using namespace System::ComponentModel;
	using namespace System::Collections;
	using namespace System::Windows::Forms;
	using namespace System::Data;
	using namespace System::Drawing;

	/// <summary>
	/// Summary for Form1
	///
	/// WARNING: If you change the name of this class, you will need to change the
	///          'Resource File Name' property for the managed resource compiler tool
	///          associated with all .resx files this class depends on.  Otherwise,
	///          the designers will not be able to interact properly with localized
	///          resources associated with this form.
	/// </summary>
	public ref class Form1 : public System::Windows::Forms::Form
	{
	public:
		Form1(void)
		{
			InitializeComponent();
			//
			//TODO: Add the constructor code here
			//
		}

	protected:
		/// <summary>
		/// Clean up any resources being used.
		/// </summary>
		~Form1()
		{
			if (components)
			{
				delete components;
			}
		}
	private: System::Windows::Forms::Button^  button1;
	protected: 
	private: System::Windows::Forms::PictureBox^  pictureBox1;
	private: System::Windows::Forms::PictureBox^  pictureBox2;

	private:
		/// <summary>
		/// Required designer variable.
		/// </summary>
		System::ComponentModel::Container ^components;

#pragma region Windows Form Designer generated code
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		void InitializeComponent(void)
		{
			System::ComponentModel::ComponentResourceManager^  resources = (gcnew System::ComponentModel::ComponentResourceManager(Form1::typeid));
			this->button1 = (gcnew System::Windows::Forms::Button());
			this->pictureBox1 = (gcnew System::Windows::Forms::PictureBox());
			this->pictureBox2 = (gcnew System::Windows::Forms::PictureBox());
			(cli::safe_cast<System::ComponentModel::ISupportInitialize^  >(this->pictureBox1))->BeginInit();
			(cli::safe_cast<System::ComponentModel::ISupportInitialize^  >(this->pictureBox2))->BeginInit();
			this->SuspendLayout();
			// 
			// button1
			// 
			this->button1->Location = System::Drawing::Point(267, 23);
			this->button1->Name = L"button1";
			this->button1->Size = System::Drawing::Size(129, 37);
			this->button1->TabIndex = 0;
			this->button1->Text = L"button1";
			this->button1->UseVisualStyleBackColor = true;
			this->button1->Click += gcnew System::EventHandler(this, &Form1::button1_Click);
			// 
			// pictureBox1
			// 
			this->pictureBox1->BackgroundImage = (cli::safe_cast<System::Drawing::Image^  >(resources->GetObject(L"pictureBox1.BackgroundImage")));
			this->pictureBox1->BackgroundImageLayout = System::Windows::Forms::ImageLayout::Stretch;
			this->pictureBox1->Location = System::Drawing::Point(40, 55);
			this->pictureBox1->Name = L"pictureBox1";
			this->pictureBox1->Size = System::Drawing::Size(174, 145);
			this->pictureBox1->SizeMode = System::Windows::Forms::PictureBoxSizeMode::StretchImage;
			this->pictureBox1->TabIndex = 1;
			this->pictureBox1->TabStop = false;
			// 
			// pictureBox2
			// 
			this->pictureBox2->BackgroundImageLayout = System::Windows::Forms::ImageLayout::Stretch;
			this->pictureBox2->Location = System::Drawing::Point(283, 66);
			this->pictureBox2->Name = L"pictureBox2";
			this->pictureBox2->Size = System::Drawing::Size(174, 145);
			this->pictureBox2->SizeMode = System::Windows::Forms::PictureBoxSizeMode::StretchImage;
			this->pictureBox2->TabIndex = 2;
			this->pictureBox2->TabStop = false;
			// 
			// Form1
			// 
			this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
			this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
			this->ClientSize = System::Drawing::Size(770, 256);
			this->Controls->Add(this->pictureBox2);
			this->Controls->Add(this->pictureBox1);
			this->Controls->Add(this->button1);
			this->Name = L"Form1";
			this->Text = L"Form1";
			(cli::safe_cast<System::ComponentModel::ISupportInitialize^  >(this->pictureBox1))->EndInit();
			(cli::safe_cast<System::ComponentModel::ISupportInitialize^  >(this->pictureBox2))->EndInit();
			this->ResumeLayout(false);

		}
#pragma endregion
	private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
				 Bitmap ^ im1=dynamic_cast<Bitmap^>(pictureBox1->Image);



int w=im1->Width;

int h=im1->Height;

Bitmap ^im2=gcnew Bitmap(w,h);

for(int x=0;x<w;x++)

for(int y=0;y<h;y++)

{

Color c=im1->GetPixel(x,y);

int grayshade=(c.R+c.G+c.B)/3;

// Y = 0.3*R + 0.59*G + 0.11*B

// int grayshade=0.299 * c.R + 0.587 * c.G + 0.114 * c.B;

im2->SetPixel(x,y,Color::FromArgb(grayshade,grayshade,grayshade));

}

pictureBox2->Image=im2;
			 }
	};
}


What I have tried:

I've searched online but really got no answer.
Posted
Updated 15-Mar-21 21:16pm
v2
Comments
CPallini 16-Mar-21 3:01am    
The error message surely conatins more details (e.g. it should report the exact offending line). Please share such details with us.
Ahmad Dalabeeh 16-Mar-21 3:05am    
System.NullReferenceException was unhandled
Message="Object reference not set to an instance of an object."
Source="System.Drawing"
StackTrace:
at System.Drawing.Image.get_Width()
at AmAma.Form1.button1_Click(Object sender, EventArgs e) in c:\users\dalbe_000\documents\visual studio 2008\projects\amama\amama\form1.h:line 122
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.Run(Form mainForm)
at main(String[] args) in c:\users\dalbe_000\documents\visual studio 2008\projects\amama\amama\amama.cpp:line 16
InnerException:


This is the full message copied
KarstenK 16-Mar-21 3:37am    
so the code isnt "perfect" (but has a severe bug and possible security issue) ;-)

When the following line
C++
int w=im1->Width;
is executed, im1 is invalid (that is it doesn't reference a valid object).
 
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You should have checked for the null reference after the dynamic_cast<>. For C++/CLI, you should use cli::safe_cast<>. Turns out that you can get Width and Height without casting to Bitmap^.

Try this.
private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) 
{
    Bitmap^ im2 = gcnew Bitmap(pictureBox1->Image->Width, pictureBox1->Image->Height);
    ...
}
 
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