Android Question How can I initialise this array?

[Arf]

Apologies if it's a stupid question, but I can't seem to get this right.

I have a custom type that contains an array of a variable number of another custom type:

Type MemoryRegionStruct(MemoryRegionType As Byte, Address As Int, Size As Int)
Type QueryResultsStruct(Command As Byte, BytesPerPacket As Byte, DeviceFamilyType As Byte, MemoryRegions() As MemoryRegionStruct)

MemoryRegions() is the problem. When I pull data out of an incoming USB packet to populate into MemoryRegion(0), the MemoryRegions array is null and I get an error:
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference

I am actually populating a single instance of a MemoryRegion and then trying to copy it to the the QueryResultsStruct, like this:

        Do While memtype <> -1
            Dim memreg As MemoryRegionStruct
            memreg.Initialize
            ref = ref + 1
            memreg.MemoryRegionType = memtype
            memreg.Address = FourBytesToInt(Request.Buffer(ref), Request.Buffer(ref+1), Request.Buffer(ref+2), Request.Buffer(ref+3))
            ref = ref + 4
            memreg.Size = FourBytesToInt(Request.Buffer(ref), Request.Buffer(ref+1), Request.Buffer(ref+2), Request.Buffer(ref+3))
            ref = ref + 4
            memtype = Request.Buffer(ref)
            'myResponse.MemoryRegions(regionref).Initialize
            myResponse.MemoryRegions(regionref) = memreg
            regionref = regionref + 1
        Loop

The error occurs on the 2nd last line within the loop, I tried to initialise the Memory (commented out line) but that too results in an error:
java.lang.NullPointerException: array == null

Any guidance gratefully received.

 

[klaus]

Try to replace:
Type MemoryRegionStruct(MemoryRegionType As Byte, Address As Int, Size As Int)
by
Type MemoryRegionStruct(MemoryRegionType() As Byte, Address As Int, Size As Int)

 

[Arf]

Thanks, tried but it won't compile - but that field should be a byte, not an array of bytes - the array should be an array of MemoryRegionStructs.
I will simplify the loop I wrote above and remove some things for clarity:

Dim myResponse As QueryResultsStruct
Do While regions < 3
            Dim memreg As MemoryRegionStruct
            memreg.Initialize
            memreg.MemoryRegionType = fetchType(regions)
            memreg.Address = fetchAddress(regions)
            memreg.Size = fetchSize(regions)

            'myResponse.MemoryRegions(regions).Initialize
            myResponse.MemoryRegions(regions) = memreg
            regions = regions + 1
Loop

 

[Jeffrey Cameron]

When you initialized your "myResponse" variable, how did you declare the MemoryRegions array? It's variable length so you will need to DIM it somewhere to a fixed size. If your length will truly be variable then I suggest using a LIST instead of an array. If the length is fixed, you could create an initialization routine:

'....
    Dim poQuery As QueryResultsStruct = NewQueryStru
'....
Public Sub NewQueryStru As QueryResultsStruct
    Dim poQ As QueryResultsStruct
    poQ.Initialize
    Dim poRegions(3) As MemoryRegionStruct
    poQ.MemoryRegions = poRegions
    Return poQ
End Sub

It wouldn't be much to add a length parameter to this function to size the region if necessary. If it is always fixed at 3 then just change your type declaration and the .Initialize for the QueryResultStruct variable will handle it.

 

[Arf]

Ah OK, now that you mention it I remember using a list last time I had a similar issue.
In this case though the number of array elements will never be more than 3 so I'll change the array to a fixed size of 3.
- just did, working. Thanks all.