Visual C++ 2017 TextBox Error

Question

I'm testing my compiling software and the tester is detecting an error with the following code:

    String^ in1;
    System::Windows::Forms::TextBox^ textBox1;
    textBox1->Text = in1;

Here is the error details:

System.NullReferenceException
HResult=0x80004003
Message=Object reference not set to an instance of an object.
Source=QMB
StackTrace:
at QMB.Form1.button1_Click(Object sender, EventArgs e) in c:\users\quant\desktop\quantum metaphysics bridge\qmb\form1.h:line 266
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(IntPtr 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\quant\desktop\quantum metaphysics bridge\qmb\form1.cpp:line 11

What should I do?

Answer 1

You have to instantiate the object instance before using it.

     String^ in1;
     System::Windows::Forms::TextBox^ textBox1 = gcnew System::Windows::Forms::TextBox;
     textBox1->Text = in1;

Answer 2

Maybe you should write one line only:

String ^in1 = textBox1->Text;

Answer 3

Hi,

I suggest you could try the following code:

String^ in1;  
 textBox1->Text = in1;  

When you add controls to the form, vs will automatically add the following statements:

private: System::Windows::Forms::TextBox^  textBox1;  

this->textBox1 = (gcnew System::Windows::Forms::TextBox());  

So you didn’t need to repeat by yourself :

System::Windows::Forms::TextBox^ textBox1;  

Best Regards,

Jeanine

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