async / await：无法将类型'void'隐式转换为'int []'

Question

I am using C# 7.1 and below async/await code give me error, Cannot implicitly convert type 'void' to 'int[]'

What is the solution for it?

static async Task Main(string[] args)
    {
        Task task1 = Task.FromResult(3);
        Task task2 = Task.FromResult(5);
        Task task3 = Task.FromResult(7);

        int[] results = await Task.WhenAll(task1, task2, task3);

        Console.ReadLine();
    }

I want to return result like

// "results" contains { 3, 5, 7 }

Answer 1

Here's how it must be:

Task<int> task1 = Task.FromResult(3);
Task<int> task2 = Task.FromResult(5);
Task<int> task3 = Task.FromResult(7);

int[] results = await Task.WhenAll(task1, task2, task3);

You were casting Task<int> to base type Task .