c# - 为什么我不能在异步方法中调试代码？

Question

我实际上是在晚上开始尝试了解有关 MongoDB 的更多信息，但我被挂断了，并且 .NET 等待/异步的东西。我正在尝试实现 MongoDB 的 site 上显示的代码.我不得不稍微修改一下，这样我才能编译我的程序。现在，我的控制台应用程序中有以下内容:

protected static IMongoClient _client;
protected static IMongoDatabase _database;

static void Main(string[] args)
{
    _client = new MongoClient();
    _database = _client.GetDatabase("test");

    GetDataAsync();
}

private static async void GetDataAsync() //method added by me.
{
    int x = await GetData();
}

private static async Task<int> GetData()
{
    var collection = _database.GetCollection<BsonDocument>("restaurants");
    var filter = new BsonDocument();
    var count = 0;
    Func<int> task = () => count; //added by me.
    var result = new Task<int>(task); //added by me.
    using (var cursor = await collection.FindAsync(filter)) //Debugger immediately exits here, goes back to main() and then terminates. 
    {
        while (await cursor.MoveNextAsync())
        {
            var batch = cursor.Current;
            foreach (var document in batch)
            {
                // process document
                count++;
            }
        }
    }

    return count; //added by me
}

当我运行应用程序时，调试器将调用我的 GetDataAsync() 方法，该方法又调用 GetData() 方法。它到达 using (var cursor = await collection.FindAsync(filter)) 行，然后立即返回以完成 main() 方法。

我在该行下方放置的任何断点都会被忽略，就像我在 GetDataAsync() 方法中放置的任何断点一样。这段代码是不是因为程序退出而没有运行？有人可以向我解释发生了什么吗？

Answer 1

因为您没有 await 执行您的 GetDataAsync 方法。当到达第一个 await 时，线程将返回给调用者。由于您没有等待任务完成，因此您的控制台应用程序将退出并且您的断点未到达。您还需要更新 GetDataAsync 方法以返回 Task 而不是 void。你不能等待无效。你应该 avoid using async void除了事件处理程序之外的任何东西。

protected static IMongoClient _client;
protected static IMongoDatabase _database;

static void Main(string[] args)
{
    _client = new MongoClient();
    _database = _client.GetDatabase("test");

    GetDataAsync().Wait(); 
    // Will block the calling thread but you don't have any other solution in a console application
}

private static async Task GetDataAsync() //method added by me.
{
    int x = await GetData();
}

private static async Task<int> GetData()
{
    var collection = _database.GetCollection<BsonDocument>("restaurants");
    var filter = new BsonDocument();
    var count = 0;
    Func<int> task = () => count; //added by me.
    var result = new Task<int>(task); //added by me.
    using (var cursor = await collection.FindAsync(filter)) //Debugger immediately exits here, goes back to main() and then terminates. 
    {
        while (await cursor.MoveNextAsync())
        {
            var batch = cursor.Current;
            foreach (var document in batch)
            {
                // process document
                count++;
            }
        }
    }

    return count; //added by me
}