为什么向数组类型 object 声明和赋值会抛出超出范围的错误？

Question

I have defined this:

DT_OrderResponseOrderHeaderOperation[] HeaderOperation = new DT_OrderResponseOrderHeaderOperation[] { };
HeaderOperation[0].DAUNO = Convert.ToString(dr["Duration"]);
HeaderOperation[0].DAUNE = Convert.ToString(dr["DurationUnit"]);

But it throws error:

Index was outside the bounds of the array.

DT_OrderResponseOrderHeaderOperation is of type array.

Answer 1

You need to add length specifier to declare array. Length specifier indicates that how many elements are contained by your array. See: Single-Dimensional Arrays

DT_OrderResponseOrderHeaderOperation[] HeaderOperation = new DT_OrderResponseOrderHeaderOperation[1];
HeaderOperation[0] = new DT_OrderResponseOrderHeaderOperation()
{
    DAUNO = Convert.ToString(dr["Duration"]),
    DAUNE = Convert.ToString(dr["DurationUnit"])
};

Or you can use this Array Initialization as follow.In this case, the length specifier is not needed because it is already supplied by the number of elements in the initialization list.

DT_OrderResponseOrderHeaderOperation[] HeaderOperation = new DT_OrderResponseOrderHeaderOperation[]
{
    new DT_OrderResponseOrderHeaderOperation()
    {
        DAUNO = Convert.ToString(dr["Duration"]),
        DAUNE = Convert.ToString(dr["DurationUnit"])
    }
};