How to fix System NullReferenceException Object reference not set to an instance of an object

Question

EDIT  This issue is resolved  good thanks to Reniuz for his 5 hours of work and research of this issue  thank s everyone   NullReferenceException  Object reference not set to an instance of an object  on the following code and I ve searched and searched and pulled my hair out for over 7-8 hours now trying to fix it   private void buttonAddEffect Click 1 object sender  EventArgs e        EffectSelectorForm effectSelectorForm   new EffectSelectorForm Effects       if  effectSelectorForm ShowDialog this     DialogResult OK                   create a new instance of the selected effect as we may want multiple copies of one effect         Effect effect    Effect Activator CreateInstance effectSelectorForm SelectedEffect GetType             audioGraph AddEffect effect           int index   checkedListBox1 Items Add effect  true           checkedListBox1 SelectedIndex   index              MessageBox Show String Format  I have  0  effects   Effects Count        Error is on the line  EffectSelectorForm effectSelectorForm   new EffectSelectorForm Effects    the class   namespace WindowsFormsApplication13       public partial class EffectSelectorForm   Form               public EffectSelectorForm ICollection lt Effect gt  effects                        InitializeComponent                listBoxEffects DisplayMember    Name               listBoxEffects DataSource   effects                     private void buttonOK Click object sender  EventArgs e                        this DialogResult   DialogResult OK              this Close                       public Effect SelectedEffect                       get                               return  Effect listBoxEffects SelectedItem                                   private void listBoxEffects DoubleClick object sender  EventArgs e                        buttonOK Click sender  e               What this is supposed to do is when the effectSelectorForm loads it should make a list of all the voice changer options but it does not do that     it loads nothing on it  I got this code from another form for changing voice in Skype and re-wrote about 400 lines of code for it to work in my app but now I have this issue and I m not giving up with all the effort I ve put in so far  If it loaded on the other project why not in this one  I ve went over code for hours over and over thinking im missing something but no   Any help would be fantastic   Stack  See the end of this message for details on invoking  just-in-time  JIT  debugging instead of this dialog box                  Exception Text                System NullReferenceException  Object reference not set to an instance of an object     at WindowsFormsApplication13 pwn4g3 buttonAddEffect Click 1 Object sender  EventArgs e  in F  Users Tom Desktop New folder New folder  2  TestApp pwn4g3 PWN4G3 MainForm2 cs line 1758    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 amp  m  MouseButtons button  Int32 clicks     at System Windows Forms Control WndProc Message amp  m     at System Windows Forms ButtonBase WndProc Message amp  m     at System Windows Forms Button WndProc Message amp  m     at System Windows Forms Control ControlNativeWindow OnMessage Message amp  m     at System Windows Forms Control ControlNativeWindow WndProc Message amp  m     at System Windows Forms NativeWindow Callback IntPtr hWnd  Int32 msg  IntPtr wparam  IntPtr lparam    Effect cs   using System  using System Collections Generic  using System Linq  using System Text   namespace JSNet            public abstract class Effect               private List lt Slider gt  sliders          public float SampleRate   get  set            public float Tempo   get  set            public bool Enabled   get  set             public Effect                         sliders   new List lt Slider gt                 Enabled   true              Tempo   120              SampleRate   44100                     public IList lt Slider gt  Sliders   get   return sliders               public Slider AddSlider float defaultValue  float minimum  float maximum  float increment  string description                        Slider slider   new Slider defaultValue  minimum  maximum  increment  description               sliders Add slider               return slider                     public abstract string Name   get                helper base methods            these are primarily to enable derived classes to use a similar            syntax to JS effects         protected float slider1   get   return sliders 0  Value              protected float slider2   get   return sliders 1  Value              protected float slider3   get   return sliders 2  Value              protected float slider4   get   return sliders 3  Value              protected float slider5   get   return sliders 4  Value              protected float slider6   get   return sliders 5  Value              protected float slider7   get   return sliders 6  Value              protected float slider8   get   return sliders 7  Value              protected float min float a  float b    return Math Min a  b             protected float max float a  float b    return Math Max a  b             protected float abs float a    return Math Abs a             protected float exp float a    return  float Math Exp a             protected float sqrt float a    return  float Math Sqrt a             protected float sin float a    return  float Math Sin a             protected float tan float a    return  float Math Tan a             protected float cos float a    return  float Math Cos a             protected float pow float a  float b    return  float Math Pow a  b             protected float sign float a    return Math Sign a             protected float log float a    return  float Math Log a             protected float PI   get   return  float Math PI               protected void convolve c float   buffer1  int offset1  float   buffer2  int offset2  int count                        for  int i   0  i  lt  count   2  i    2                                float r   buffer1 offset1   i                   float im   buffer1 offset1   i   1                   float cr   buffer2 offset2   i                   float ci   buffer2 offset2   i   1                   buffer1 offset1   i    r   cr - im   ci                  buffer1 offset1   i   1    r   ci   im   cr                                    public virtual void Init                                 public abstract void Slider              public virtual void Block int samplesblock                                 public abstract void Sample ref float spl0  ref float spl1            public override string ToString                         return Name

User · Answer

If the problem is 100  here  EffectSelectorForm effectSelectorForm   new EffectSelectorForm Effects     There s only one possible explanation  property variable  Effects  is not initialized properly    Debug your code to see what you pass to your objects   EDIT after several hours  There were some problems    MEF attribute  Import  didn t work as expected  so we replaced it for the time being with a manually populated List lt    While the collection was null  it was causing exceptions later in the code  when the method tried to get the type of the selected item and there was none  several event handlers weren t wired up to control events   Some problems are still present  but I believe OP s original problem has been fixed  Other problems are not related to this one

User · Answer

During debug  break on all exceptions thrown  Debug- Exceptions  Check all  Thrown  exceptions  F5  the code will stop on the offending line

User · Answer

I had the same problem but it only occurred on the published website on Godaddy  It was no problem in my local host   The error came from an aspx cs  code behind file  where I tried to assign a value to a label  It appeared that from within the code behind  that the label Text appears to be  null  So all I did with change all my Label Text properties in the ASPX file from Text      to Text       The problem disappeared   I don   t know why the error happens from the hosted version but not on my localhost and don   t have time to figure out why   But it works fine now

User · Answer

I was getting this same error  but for me this was due to a method in a base class  in Project A  having the output type changed from a non-void type to void   A child class existed in Project B  which I didn t want used and had marked obsolete  that I missed when performing this update and hence started throwing this error      1 CSC   error CS8104  An error occurred while writing the output file  System NullReferenceException  Object reference not set to an instance of an object    Original Code      Obsolete  Calling this method will throw an error    public override CompletionStatus Run         throw new CustomException  Run process not supported         Revised Code      Obsolete  Calling this method will throw an error    public override void Run         throw new CustomException  Run process not supported

[c#] How to fix System.NullReferenceException: Object reference not set to an instance of an object

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