How to transfer the localvalue of one interface to another interface?

But if i create ri!case at second interface how can i make sure it is not null, any interface create ri!value is null automatically right?

You will likely need to map the rule inputs together from the child interface to the parent. For example, suppose you have a rule input for ri!case on the child interface. You will need to create a second rule input to match that on the parent interface and map them together like this:

rule!ChildInterface(case: ri!case)

Then, any changes you make in the child interface will also be saved to the parent.

for example the first interface fill a!save(target:ri!username,value:"SAAAAM"), then the second interface can retrieve like rule!interface1().username, is this ok?

how to let ri!value be retrieved from previous interface then passed to second interface?

but how to let ri!value get retrieve from another interface? I tried lots of times

i meant ri!value as interface value. My bad!

I never see interface value before only ri!value and local!value

it would be best if you give a example

You should consider changing the local variable to an interface variable. Local variables value can't be passed.