Array question

[Michael Rodriguez]

What is the proper way to declare and initialize an array of datasets?
Would it go like this:

private DataSet[] myDataSets;

DataSet ds1 = new DataSet(); // initialize the dataset
DataSet ds2 = new DataSet(); // initialize the dataset

myDataSets = new DataSet[2]; // does this create the array, the datasets,
or both?

myDataSets[0] = ds1;
myDataSets[1] = ds2;

// what is now the difference between these two lines?

ds1.Dispose();
myDataSets[0].Dispose();

TIA,

Mike Rodriguez

 

[Nicholas Paldino [.NET/C# MVP]]

Michael,

When you do something like this:

// Create the array.
private DataSet[] myDataSets;

All that does is declare the array. For an array of reference types
like this, the elements are all initialized to null. It isn't until you
assign the specific elements that there is something in there to work with.

As for the following statements:

ds1.Dispose();
myDataSets[0].Dispose();

They both do the same thing, since they both point to the same instance
(assigning to an array element only copies the reference to the instance, it
doesn't copy the instance itself).

Hope this helps.

 

[Michael Rodriguez]

Michael,

When you do something like this:

// Create the array.
private DataSet[] myDataSets;

All that does is declare the array. For an array of reference types
like this, the elements are all initialized to null. It isn't until you
assign the specific elements that there is something in there to work
with.

Hi Again, Nicholas <g>

So are you saying this code is the correct form for creating the array and
the datasets:

DataSet ds1 = new DataSet();
DataSet ds2 = new DataSet();

myDataSets = new DataSet[2];

myDataSets[0] = ds1;
myDataSets[1] = ds2;


Thanks!

Mike Rodriguez

 

[Nicholas Paldino [.NET/C# MVP]]

Michael,

Well, if you wanted to create a two element array and populate each
element with an empty dataset, yes! =)

If you wanted to do it for N number of elements, you could do:

public static DataSet[] CreateAndPopulateDataSetArray(int elements)
{
// If elements is less than zero, then throw an exception.
if (elements < 0)
{
// Throw an exception.
throw new ArgumentException("The elements parameter must be a
non-negative value.", "elements");
}

// Create the array.
DataSet[] retVal = new DataSet[elements];

// Cycle through the elements, and create a new instance.
for (int index = 0; index <= retVal.Length; ++index)
{
// Create a new instance.
retVal[index] = new DataSet();
}

// That's all folks.
return retVal;
}

Michael,

When you do something like this:

// Create the array.
private DataSet[] myDataSets;

All that does is declare the array. For an array of reference types
like this, the elements are all initialized to null. It isn't until you
assign the specific elements that there is something in there to work
with.

Hi Again, Nicholas <g>

So are you saying this code is the correct form for creating the array and
the datasets:

DataSet ds1 = new DataSet();
DataSet ds2 = new DataSet();

myDataSets = new DataSet[2];

myDataSets[0] = ds1;
myDataSets[1] = ds2;


Thanks!

Mike Rodriguez

 

[Michael Rodriguez]

Michael,

public static DataSet[] CreateAndPopulateDataSetArray(int elements)
{
// If elements is less than zero, then throw an exception.
if (elements < 0)
{
// Throw an exception.
throw new ArgumentException("The elements parameter must be a
non-negative value.", "elements");
}

// Create the array.
DataSet[] retVal = new DataSet[elements];

// Cycle through the elements, and create a new instance.
for (int index = 0; index <= retVal.Length; ++index)
{
// Create a new instance.
retVal[index] = new DataSet();
}

// That's all folks.
return retVal;
}

That's what I needed to know! Thanks, Nicholas.

 

[Bob Grommes]

Michael,

This will give you an array with two empty DataSets. If that's what you
want, then this would be more efficient:

private DataSet[] myDataSets = new DataSet[2];
....
myDataSets[0] = new DataSet();
myDataSets[1] = new DataSet();

There is generally no point in housing them in an array *and* then having
separate variables pointing to the same objects.

--Bob

Michael,

When you do something like this:

// Create the array.
private DataSet[] myDataSets;

All that does is declare the array. For an array of reference types
like this, the elements are all initialized to null. It isn't until you
assign the specific elements that there is something in there to work
with.

Hi Again, Nicholas <g>

So are you saying this code is the correct form for creating the array and
the datasets:

DataSet ds1 = new DataSet();
DataSet ds2 = new DataSet();

myDataSets = new DataSet[2];

myDataSets[0] = ds1;
myDataSets[1] = ds2;


Thanks!

Mike Rodriguez

 

[Michael Rodriguez]

Michael,

This will give you an array with two empty DataSets. If that's what you
want, then this would be more efficient:

private DataSet[] myDataSets = new DataSet[2];
...
myDataSets[0] = new DataSet();
myDataSets[1] = new DataSet();

There is generally no point in housing them in an array *and* then having
separate variables pointing to the same objects.

--Bob

Hi Bob,

You make a valid point. However, in my case the array will hold datasets
that have already been created elsewhere.

Thanks,

Mike