异步任务<string>不返回正确的结果，WebClient.OpenReadTaskAsync()</string>

Question

in winform program(C#)，async Task not return correct result，my codes are below：

public async void method1()
{
    await Task.Run(() =>
        {
            System.Threading.Thread.Sleep(2000);
            if (textBox1.InvokeRequired)
            {
                textBox1.Invoke(new Action(() => textBox1.Text += "AAAAAAAAAAAA\r\n"));
            }
        });

    if(textBox1.InvokeRequired)
    {
        textBox1.Invoke(new Action(() => textBox1.Text += "BBBBBBBBBB\r\n"));
    }
}

public async Task<string> method2()
{
    string result = string.Empty;
    System.Net.WebClient wc = new System.Net.WebClient();
    Stream st = await wc.OpenReadTaskAsync("https://msdn.microsoft.com/en-us/library/hh191443(v=vs.110).aspx#What Happens in an Async Method");
    //Task<Stream> st= wc.OpenReadTaskAsync("https://msdn.microsoft.com/en-us/library/hh191443(v=vs.110).aspx#What Happens in an Async Method");
    //Stream st2 = st.Result;
    StreamReader sr = new StreamReader(st);
    result = sr.ReadToEnd();

    return result;
}
private void button1_Click(object sender, EventArgs e)
{
    textBox1.Text += method2()+"\r\n";

    method1();
    textBox1.Text += "CCCCCCCCCCCC\r\n";
}

Output:

System.Threading.Tasks.Task`1[System.String]

CCCCCCCCCCCC

AAAAAAAAAAAA

My question:

1)method2,i want to return the page content,but in fact,it is "System.Threading.Tasks.Task`1[System.String]"

2)string "BBBBBBBBBB" not been added in textBox1,is this why?

Answer 1

Here you have the code with some changes (textBox for richTextBox) and some clarifications.

string "BBBBBBBBBB" not been added in textBox1,is this why?

InvokeRequired only return true if you call it from a worker thread.

method2,i want to return the page content,but in fact,it is "System.Threading.Tasks.Task`1[System.String]"

Since method1 return Task you have few options, call method.result (not recommende, it will block the main thread) or use async/await to get the result.

    public async void method1()
    {
        await Task.Run(() =>
        {
            System.Threading.Thread.Sleep(2000);
            if (richTextBox1.InvokeRequired)
            {
                richTextBox1.Invoke(new Action(() => richTextBox1.Text += "AAAAAAAAAAAA\r\n"));
            }
        });

        //This in main thread so InvokeRequired == false
        //if (textBox1.InvokeRequired)
        //{
        //    textBox1.Invoke(new Action(() => textBox1.Text += "BBBBBBBBBB\r\n"));
        //}            
        richTextBox1.Text += "BBBBBBBBBB\r\n";
    }

    public async Task<string> method2()
    {
        string result = string.Empty;
        System.Net.WebClient wc = new System.Net.WebClient();
        var st = await wc.OpenReadTaskAsync("https://msdn.microsoft.com/en-us/library/hh191443(v=vs.110).aspx#What Happens in an Async Method");
        //Task<Stream> st= wc.OpenReadTaskAsync("https://msdn.microsoft.com/en-us/library/hh191443(v=vs.110).aspx#What Happens in an Async Method");
        //Stream st2 = st.Result;
        StreamReader sr = new StreamReader(st);
        result = sr.ReadToEnd();

        return result;
    }
    private async void button1_Click(object sender, EventArgs e)
    {
        //await is needed to get string insted of Task<string>
        richTextBox1.Text = await method2(); 

        method1();
        richTextBox1.Text += "CCCCCCCCCCCC\r\n";
    }

Answer 2

Change your button click event like this

private async void Button_Click..

Replace

textBox1.Text += method2()+"\r\n";

To

textBox1.Text += await method2()+"\r\n";