c# - Object reference not set to an instance of an object. [NullReferencceException was unhandled] -

related topic:

if condition mdi parent control

i need call text label in dtexteditor (form) label in frmmain (form) . , use timer instead of button since follow answer here: communicate between 2 windows forms in c#

which leads to:

frmmain.cs:

private dtexteditor a;         public frmmain(form callingform)         {             = callingform dtexteditor;             initializecomponent();         }          private void timercountline_tick(object sender, eventargs e)         {                 a.lblcl = lblcountline.text;         } 

dtexteditor.cs

public string lblcl //rich         {             { return lblcountline.text; }             set { lblcountline.text = value; }         } 

but thing error shows:

what should remove error? pls lot!

check followings :
1- check variable in constructor not null
2-after initializecomponent can design objects :

public frmmain(form callingform) { initializecomponent(); = callingform dtexteditor; } 

3- assignment both side seems same : a.lblcl = lblcountline.text means :

lblcountline.text = lblcountline.text  : lblcountline.text = value !! 

4- check timer interval , enable after initializecomponent ( set in designto false )

public frmmain(form callingform) { initializecomponent(); = callingform dtexteditor; timer1.enabled=true; }