C＃中带有数组的NullReferenceException

Question

I want to create an array containing all the Pushpin objects I am dealing with. While trying to populate the Array, I am getting a NullReferenceException Unhandled error thrown. I have read as much documentation as I can find and cannot work out what is going on.

I have tried at least the following:

Pushpin[] arrayPushpins;
int i = 0;
foreach (Result result in arrayResults)
                {
                    Pushpin pin;
                    pin = new Pushpin();
                    pin.Location = d;
                    myMap.Children.Add(pin);
                    arrayPushpins[i] = new Pushpin();
                    arrayPushpins.SetValue(pin, i);;
                    i++;
                }

AND...

Pushpin[] arrayPushpins;
int i = 0;
foreach (Result result in arrayResults)
                {
                    Pushpin pin;
                    pin = new Pushpin();
                    pin.Location = d;
                    myMap.Children.Add(pin);
                    arrayPushpins[i] = new Pushpin();
                    arrayPushpins[i] = pin;
                    i++;
                 }

And nothing seems to work... I get the NullReference error every time. Any ideas? Many thanks! Will.

Answer 1

The problem is that you don't initialize your array:

Pushpin[] arrayPushpins = new Pushpin[10]; // Creates array with 10 items

You might consider using IEnumerable<Pushpin> if you don't know the number of items in advance, eg:

IEnumerable<Pushpin> pushpins = new List<Pushpin>

Answer 2

You didn't initialize the array

 Pushpin[] arrayPushpins = new Pushpin[/*number goes here*/];
    int i = 0;
    foreach (Result result in arrayResults)
                    {
                        Pushpin pin;
                        pin = new Pushpin();
                        pin.Location = d;
                        myMap.Children.Add(pin);
                        arrayPushpins[i] = new Pushpin();
                        arrayPushpins.SetValue(pin, i);;
                        i++;
                    }

Edited to add: I'd avoid using a raw array, and go with something like a List<Pushpin> instead

Answer 3

I think you should use a list instead of an array. That way, you won't have to know in advance how many elements will you have in your list.

Answer 4

In your code, the array is only declared, not initialized. You need to initialize it with the new keyword.

Pushpin [] arrayPushpins= new Pushpin[50]; 

As the other answers recommend, you can use lists or collections.