异步功能-先启动先结束-C＃WPF

Question

i have a problem , i have a textbox controle, i activated the keyup function, so when the user write an ID in the system , the programe start searching until the it found the user.

im using it with this example code below

private async void PNationalNo_KeyUp(object sender, KeyEventArgs e)
{            
        string Ptext = Textbox.text;
        string ResposeDataP  = ""; 

        await Task.Run(() =>
        {
            ResposeDataP = RunAsyncGetOnePatient(Ptext, GV.AccountID).Result;
        });

        Patient1 = JsonConvert.DeserializeObject<PatientM>(ResposeDataP);


        if (Patient1 != null)
        {

            WrongMsg1.Text = "user '" + Patient1 .PatientFullName.ToLower() + "' have this ID number!";
        }
        else
        {
            WrongMsg1.Text = "there is no user have this ID!!";
        }
}

the problem with this code , sometimes when the code find the result in the last async tanks , 1 of the tasks take more time than the finale one , so the programe print the result of that late function !! not the final one ?!! (( there is no user have this ID!!)), becouse its not the last function in the async code , so how can i solve this problem ?!!

Updated from comments

i mean if the user ID = "123" in the database, when i press 1 this is the first function.

Then when i press 2, the textbox = "12"

When i press 3 textbox = "123"

So it should print in the WrongMsg1.Text that the user is found, but the problem is sometimes the function of textbox = "12" finish after the function of "123" , so it print in the "there is no user have this id!!" .

did u understand me? because async function number 2 , finished after the last function.

Answer 1

It seems to be a typical race condition. Since Task.Run executes in a background thread you no longer have control over the order of execution which means that the input of the second character is evaluated after the third character. So you have to find a way to make sure the order of execution is still correct when you are back in control.

A possible solution might be to check whether the text in the text box is still the same after the async Task finished:

    private async void PNationalNo_KeyUp(object sender, KeyEventArgs e)
        {            
            string Ptext = Textbox.text;
            string ResposeDataP  = ""; 

            await Task.Run(() =>
            {
                ResposeDataP = RunAsyncGetOnePatient(Ptext, GV.AccountID).Result;
            });

            if (Textbox.text != Ptext)
            {
                return;
            }

            Patient1 = JsonConvert.DeserializeObject<PatientM>(ResposeDataP);


            if (Patient1 != null)
            {

                WrongMsg1.Text = "user '" + Patient1 .PatientFullName.ToLower() + "' have this ID number!";
            }
            else
            {
                WrongMsg1.Text = "there is no user have this ID!!";
            }
    }