With regular ERC20 tokens we have method approve(to, amount) and so I can approve to someone to take specified amount of my tokens later with transferFrom(from, to, amount).
Is there any way to approve Ether to be taken from my account?
[Ethereum] How to do approve and transferFrom for Ether
ether
Related Solutions
It sounds like you have a few fundamental things you're getting confused about with contracts and ether: Firstly, you as a human (or company) owns an Ethereum address which you can use to transfer ether into and out of (your wallet). When you deploy a contract, that action is a transaction in the Ethereum blockchain, and so has to come from some Ethereum address. So, you sign it with your wallet address, and the Ethereum virtual machine creates a brand new address (separate from your own wallet address) for the new contract.
Anyone can send ether to a contract. But getting ether back out is dependent on the code of the contract itself. You need to pick how that's going to work as you develop it.
So, to answer your questions:
The gas [to deploy the contract] will be extracted from the ether that the account has right?
The account that's deploying the contract (your wallet) must have enough ether in it to pay for the gas to create the contract, yes. The newly-created contract will be created with no ether in it (unless the code of the contract does something that transfers ether in).
The gas is said to be consistent but the number of transaction cannot be predicted. It can be few or huge so how we calculate the ether we need in first place?
The amount of gas needed to create a new Contract depends on the code complexity of the Contract itself. You can use the estimateGas() function in web3 to calculate that from the compiled bytecode of your contract before you deploy it (more details).
How you should set up the ether amount and make sure later it not runs out
Both your own personal wallet and any deployed contract can receive ether paid to it. So, if your deployed contract needs to send ether to someone, and it runs out, you can send more to it at a later time. However, it's possible that a contract, once deployed, will not ever need any ether, since it doesn't pay for the gas needed to trigger its methods. A transaction needs to be crafted to call functions on that contract, and that calling function has to come from a human-owned contract, and the human-owned contract pays for the gas of the transaction.
As stated by Thomas and Raghav your problem is in the method forwardAllRaisedFunds that uses weiRaised to transfer funds out of your contract, if that variable has a value larger than available the transfer will fail.
There is a trick to increment the balance of a contract without executing the fallback function.
If you selfdestruct a dummy contract and put your contract as target. It will increment the balance keeping the variable weiRaised unchanged.
Best Answer
You could do it by coding pretty much the same logic as the token does for it's own balance.
A deposit function takes ether from msg.sender and stores it in the contract while registering the amount deposited by that address in a mapping state variable.
An approve function would set how much ether the contract is allowed to transfer from the origin address.
A transferFrom function would modify the _from account balance and _to account balance accordingly (up to the amount that was approved).
Here's a main difference with the token logic. You would have to have a withdraw function that allows the msg.sender to reduce its balance and generate an Ether transfer from the contract to msg.sender. (This would be done to prevent possible DoS attacks on the contract).