Transaction fees withdraw/deposit in

Question

I made transactions on a simple EVM DEX contract.

I initially called the approve method which only triggered balances.withdraw event. I understand that this event is triggered as calling this write-method requires transaction fees.

I then triggered the addLiquidity method on the contract which is payable and thus should receive the native token while this method is executed. While executing this transaction, I see that there are both balances.withdraw and balances.deposit. I don't understand why it didn't just withdraw all the required transaction fee at once, instead of withdrawing a larger portion and then depositing back some later on.

What is the cause for this?

Answer 1

This has to do with how the balances pallet handles taking funds for gas vs taking funds THEN giving them to another account - your contract in this case.

When you deploy a contract you will see even more events related to balances where an account is created, funded with the storage deposit, etc, etc.