Iteract with arrays from another contract - solidity

Question

Does anyone know how can I read meanings of variables in the array from another contract ? For example:
pragma solidity 0.8.7;
contract Contract1{
uint[] newData ;
constructor(uint _i){
newData.push(_i);
}
}
interface IContract1 {
function newData() external returns(uint[] memory);
}
contract Contract2 {
uint public newOne;
function foo(address _addr, uint _i) external{
newOne = IContract1(_addr).newData()[_i];
}
}
This code has compiled success in the Remix, but I have an error when I trying call foo()

Answer 1

Contract1.newData is an internal (default visibility when you don't specify it) property.
But the interface IContract1 defines an external function named newData() (without the index argument).
You can modify the newData property to have a public visibility, for which the compiler autogenerates a getter function (with the index argument).
Then you also need to update the function definition in the interface, so that it contains the index argument and returns just one item (and not the whole array).
pragma solidity ^0.8;
contract Contract1 {
// changed visibility to `public`
uint[] public newData;
constructor(uint _i){
newData.push(_i);
}
}
interface IContract1 {
// added `_index` argument
// changed the return value to one item of the array
function newData(uint256 _index) external returns(uint);
}
contract Contract2 {
uint public newOne;
function foo(address _addr, uint _i) external{
// changed the call to the getter function
// instead of trying to access the property directly
newOne = IContract1(_addr).newData(_i);
}
}
Note that the Contract1 constructor pushes the first item to the array, so you need to pass 0 (as for the first index) to the foo() function argument uint _i.
Repro steps:
Deploy Contract1 passing it 123 as constructor param. Deployed to address 0x456.
Deploy Contract2
Execute Contract2 function foo(0x456, 0), which will effectively set Contract2.newOne value to 123.