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如何从异步例程更新UI,而无需启动或调用[duplicate]

winforms c#

-1

Mist · 技术社区 · 7 年前

我看到许多代码,他们使用BeginInvoke从另一个线程更新UI。是否可以从异步函数更新UI而无需启动InVoke?

private async void button1_Click(object sender, EventArgs e)
        {
            button1.Enabled = false;
            var count = 0;

            await Task.Run(() =>
            {
                for (var i = 0; i <= 500; i++)
                {
                    count = i;
                    BeginInvoke((Action)(() =>
                    {
                        label1.Text = i.ToString();

                    }));
                   Thread.Sleep(100);
                }
            });

            label1.Text = @"Counter " + count;
            button1.Enabled = true;
        }

看到下面的代码,我已经从一个链接,显示没有BeginInvoke,我们可以更新用户界面时使用task.run。

private readonly SynchronizationContext synchronizationContext;
private DateTime previousTime = DateTime.Now;

public Form1()
{
    InitializeComponent();
    synchronizationContext = SynchronizationContext.Current;
}

private async void button1_Click(object sender, EventArgs e)
{
    button1.Enabled = false;
    var count = 0;

    await Task.Run(() =>
    {
        for (var i = 0; i <= 5000000; i++)
        {
            UpdateUI(i);
            count = i;
        }
    });

    label1.Text = @"Counter " + count;
    button1.Enabled = true;
}

public void UpdateUI(int value)
{
    var timeNow = DateTime.Now;

    if ((DateTime.Now - previousTime).Milliseconds <= 50) return;

    synchronizationContext.Post(new SendOrPostCallback(o =>
    {
        label1.Text = @"Counter " + (int)o;
    }), value);             

    previousTime = timeNow;
}

告诉我 synchronizationContext和BeginInvoke 两者都一样吗?应该使用哪个线程更新UI?哪一个效率最高?

请指导我,我是async/await&方面的新手;任务使用情况。

3 回复 | 直到 7 年前

Alexander Petrov 7 年前

使用 Progress 班级。

private async void button1_Click(object sender, EventArgs e)
{
    button1.Enabled = false;
    var count = 0;

    // The Progress<T> constructor captures UI context,
    // so the lambda will be run on the UI thread.
    IProgress<int> progress = new Progress<int>(value =>
    {
        label1.Text = value.ToString();
    });

    await Task.Run(() =>
    {
        for (var i = 0; i <= 500; i++)
        {
            count = i;
            progress.Report(i);
            Thread.Sleep(100);
        }
    });

    label1.Text = @"Counter " + count;
    button1.Enabled = true;
}

Henk Holterman 7 年前

要避免的是 Task.Run()

private async void button1_Click(object sender, EventArgs e)
{
    button1.Enabled = false;
    var count = 0;

    for (var i = 0; i <= 500; i++)
    {
        count = i;          
        label1.Text = i.ToString();
        await Task.Delay(100);         // do async I/O or Task.Run() here
    }    
}

Fabio 7 年前

Invoke .

private async Task UpdateDatabase()
{
    using (var connection = new SqlConnection(connectionString))
    using (var command = connection.CreateCommand())
    {
        command.CommandText = "SELECT Id FROM Table";
        await connection.OpenAsync();
        using (var reader = await command.ExecuteReaderAsync())
        {
            var rowsCount = 0;
            // Since execution will happen on same thread 
            // you will be able update UI controls.
            Label1.Text = $"Rows: {rowsCount}";

            while (await reader.ReadAsync())
            {
                rowsCount ++;
                Label1.Text = $"Rows: {rowsCount}";
            }
        }
    }
}

private async void button1_Click(object sender, EventArgs e)
{
    button1.Enabled = false;

    await UpdateDatabase();

    button1.Enabled = true;
}

对于希望使用“进度”信息更新UI的特定情况,可以使用 BackgroundWorker Progress