SSRS - Expression to create string for reporting heading

Question

I have a report which has 6 parameters within it. What I would like to do is make these parameters part of my report heading. My parameters are as follows:

@BMDataType1  Text
@BMDataComp1  Float
@BMDataType2  Text
@BMDataComp2  Float
@BMDataType3  Text
@BMDataComp3  Float

There will always be an @BMDataType1 and @BMDataComp1 parameter passed, the others can be null. What I need the heading to look like is if only @BMDataType1 and @BMdataComp1 are passed then the heading should be for example:

Benchmark1 100% Benchmark Constituents

So far I have coded for this below:

=Parameters!BMDataType1.Value + " " + Parameters!BMDataComp1.Value.ToString + "%" + " Benchmark Constituents"

However if @BMDataType2 and @BMDataComp2 are populated then I need the heading to look like this:

Benchmark1 50% Benchmark2 50% Benchmark Constituents

Same for if 3 are passed then:

Benchmark1 50% Benchmark2 30% Benchmark3 20% Benchmark Constituents

There will never be say a Benchmark 1 and Benchmark 3. It will only be ever 1, or 1 and 2 or 1, 2 and 3.

Can someone point me in the right direction of how to write the IIF statement for this checking to see if Benchmark2 and Benchmark3 parameters are NULL?

Thanks

EDIT:

After some work on this I came up with the following code, but I'm still getting:

"Object reference not set to an instance of an object"

My code is the following:

=IIF(
    IIF(IsNothing(Parameters!BMDataType1.Value),1,0)=0 AND IIF(IsNothing(Parameters!BMDataType2.Value),1,0)=1 AND IIF(IsNothing(Parameters!BMDataType3.Value),1,0)=1
,   Parameters!BMDataType1.Value + " " + Parameters!BMDataComp1.Value.ToString + "%" + " Benchmark Constituents"
, IIF(
    IIF(IsNothing(Parameters!BMDataType1.Value),1,0)=0 AND IIF(IsNothing(Parameters!BMDataType2.Value),1,0)=0 AND IIF(IsNothing(Parameters!BMDataType3.Value),1,0)=1
,   Parameters!BMDataType1.Value + " " + Parameters!BMDataComp1.Value.ToString + "%" + " " + Parameters!BMDataType2.Value + " " + Parameters!BMDataComp2.Value.ToString + "%" + " Benchmark Constituents"
, IIF(
    IIF(IsNothing(Parameters!BMDataType1.Value),1,0)=0 AND IIF(IsNothing(Parameters!BMDataType2.Value),1,0)=0 AND IIF(IsNothing(Parameters!BMDataType3.Value),1,0)=0
,   Parameters!BMDataType1.Value + " " + Parameters!BMDataComp1.Value.ToString + "%" + " " + Parameters!BMDataType2.Value + " " + Parameters!BMDataComp2.Value.ToString + "%" + " " + Parameters!BMDataType3.Value + " " + Parameters!BMDataComp3.Value.ToString + "%" + " Benchmark Constituents"
, " ")))

However if all 3 parameters are not null it returns no error and it populates the heading as I would like it displayed. How can this be?

Answer 1

I found the solution to this and my code is as of below:

=Parameters!BMDataType1.Value + " " + CStr(Parameters!BMDataComp1.Value) + "% " 
+ IIF(IIF(IsNothing(Parameters!BMDataType2.Value),1,0)=0,Parameters!BMDataType2.Value + " " + CStr(Parameters!BMDataComp2.Value)+"%","") + " "
+ IIF(IIF(IsNothing(Parameters!BMDataType3.Value),1,0)=0,Parameters!BMDataType3.Value + " " + CStr(Parameters!BMDataComp3.Value)+"%","") + " Benchmark Constituents"

For whatever reason it was not liking the .ToString which was returning "Oject reference not set to an instance of an object". By wrapping this in CStr I was able to remove the error and get the solution I required.

Thanks for all the responses, they all helped.