如何使用 C# switch 语句的返回值以 true 或 false 退出任务？

Question

I have this code:

public async Task PickCard()
{
    switch (Settings.Co)
    {
        case CO.Random: Random(); break;
        case CO.FirstToLast: ArrangeCardOrder(true); break;
        case CO.LastToFirst: ArrangeCardOrder(false); break;
    }
    await ShowCard();
}

I am going to be modifying Random() , ArrangeCardOrder(true) and ArrangeCardOrder(false) to return a true or false .

Is there a way that I can get that information from the switch and if they methods return true then call await ShowCard and then exit PickCard with a true and if the methods return false , simply exit PickCard with a false ?

Answer 1

Currently that's just a switch statement . To use a switch expression you need to change the syntax a bit - as well as using C# 8. You'll also want to change the return type so that PickCard can indicate the result.

public async Task<bool> PickCard()
{
    // This is a switch *expression* instead of a switch *statement*.
    // Switch expressions were introduced in C# 8.
    bool result = Settings.Co switch
    {
        CO.Random => Random(),
        CO.FirstToLast => ArrangeCardOrder(true),
        CO.LastToFirst => ArrangeCardOrder(false),
        // Adjust for whatever you want to do
        _ => throw new InvalidOperationException("Invalid setting")
    }

    if (result)
    {
        await ShowCard();
    }
    return result;
}

Answer 2

Something like this? Can obviously be adjusted to fit your exact needs better...

var succeeded = false;

switch (Settings.Co)
{
    case CO.Random: 
        succeeded = Random(); 
        break;
    (...)    
}

var result = false;
if(succeeded){
    result = await ShowCard();

    // or alternatively:
    // await ShowCard();
    // return true;
}

return result;