static int m=0;
dualDisplay.setOnClickListener(new OnCli....{
onClick()
{
if(dualcamera1.isChecked())
m++; // you can save this as checked somewhere
if(dualcamera2.isChecked())
m++; // you can save this as checked somewhere
if(dualcamera3.isChecked())
m++; // you can save this as checked somewhere
if(dualcamera4.isChecked())
m++; // you can save this as checked somewhere
}
});
if(m>2 || m<2)
// show error message
else
// code here