Cannot convert from "String" to "DataSourceAlias"

Dear DS developers,

We have a chart (CHART_5) that is dynamically filled with a datasource, the user can select the datasource. On the chart I want to create an OnClick event with the following functionality:

- Read the datasource from CHART_5 (eg. DS_3)

- Based on this datasource, select the detailed datasource (eg. DS_3_DETAIL)

- Assign this detailed datasource to a crosstab and navigationpanel.

Now I've the following piece of code:

Where "g_datasource_detail" is a global variable Type String.

Now the following error will occur: Cannot convert from "String" to "DataSourceAlias".

I also tried to change the type of the global variable "g_datasource_detail" to Type DataSourceAlias, but then the error "Cannot convert from "DataSourceAlias" to "String"" will appear.

Can anybody help me with this?

Regards,

Pieter