C＃中的折线数组无法运行

Question

i am trying to create a polyline array so that the end user can add as many polylines to his canvas as he wants to, the code won't run and wile debugging it writes: "Exception has been thrown by the target of an invocation." here is a part of the code

Polyline[] linije = new Polyline[10];        
linije[0].Stroke = System.Windows.Media.Brushes.Black;           
linije[0].StrokeThickness = 1;        
linije[0].Points = poli.Points;          
canvas1.Children.Add(linije[0]);

Answer 1

You have a null reference exception because you don't create a Polyline instance in element 0 of your array.

Polyline[] linije = new Polyline[10];     
linije[0] = new Polyline();  // Create the Polyline object!!!
linije[0].Stroke = System.Windows.Media.Brushes.Black;           
linije[0].StrokeThickness = 1;        
linije[0].Points = poli.Points;          
canvas1.Children.Add(linije[0]);

Remember that creating an array of a certain type DOESN'T create the objects for each element in that array. You can easily spot that by using the debugger . If you add a breakpoint just after after the line Polyline[] linije = new Polyline[10] and you add a watch for linije[0] you'll see that it is null.