异步调用多个方法

Question

Is there a way to call multiple methods at the same time? I have a winforms app that loads an incredible amount of data upon loading:

private void form1_Load(object sender, EventArgs e)
{
    LoadValues1();
    LoadValues2();
    LoadValues3();
    LoadValues4();
    LoadValues5();
    LoadValues6();
    LoadValues7();
    LoadValues8();
}

These methods retrieve data and populate DevExpress LookUpEdits (similar to windows dropdownlists), so they all look like this:

DBContext dbContext = new DBContext();
ObservableCollection<string> values1 = 
    new ObservableCollection<string>((from i in dbContext.Items
                                      where i.Value1 != null
                                      && i.Value1.Length > 0
                                      orderby i.Value1
                                      select i.Value1).Distinct());

lookupValues1.Properties.DataSource = descModelYear;
DevExpress.XtraEditors.Controls.LookUpColumnInfoCollection colInfo = lookupValues1.Properties.Columns;
colInfo.Clear();
colInfo.Add(new DevExpress.XtraEditors.Controls.LookUpColumnInfo("Column"));
colInfo[0].Caption = "Values 1";

and some of these methods take a while to complete, yet none of them are dependent on one another, so I thought I could do them all at the same time:

Task.Factory.StartNew(() => LoadValues1());
Task.Factory.StartNew(() => LoadValues2());
etc.

but I keep getting an error when the 2nd task is run, saying a control can't be accessed from a different thread than what it was created on.

Any help is appreciated!

Answer 1

As others have pointed out you need to ensure that when accessing UI elements you need to make sure that you do it on the proper read. This is easy to do using the Task Parallelism Library like so:

private TaskScheduler m_TaskScheduler = TaskScheduler.FromCurrentSynchronizationContext();

Once you have the TaskScheduler you can schedule your tasks to run on the UI thread like this:

Task.Factory.StartNew(() => 
{
     LoadValues1();
}, CancellationToken.None, TaskCreationOptions.None, m_TaskScheduler);

The caveat here is that running all of your tasks on the UI thread might still lock things up on you. I would recommend that you create some sort of class or set of collections that you can populate the relevant information in to and then once all the data is there for you to call another method on the UI thread that just binds your controls to the data or does whatever UI specific actions you need.

Answer 2

When manipulating UI controls, you must be do so on the same thread that created the control. In this case, you should just run those methods that modify the UI synchronously. If all of the methods modify the UI, you should split the work so that only the code that modifies the UI is invoked on the UI thread.

In general, you can use InvokeRequired to check whether you are on the right thread, and Invoke to run a method on the UI thread.

Answer 3

You should separate out your logic in distinct units and try to get your UI logic in one place.

//private fields
private readonly DBContext _dbContext = new DBContext();

private Task<ICollection<string>> GetValues1()
{
    return Task.Run(() =>
            {
                return (from i in _dbContext.Items
                        where i.Value1 != null
                        && i.Value1.Length > 0
                        orderby i.Value1
                        select i.Value1)
                        .Distinct()
                        .ToList();
             };
}

private void LoadUIElements1(ICollection<string> values)
{
    var observableValues = new ObservableCollection<string>(values);

    lookupValues1.Properties.DataSource = descModelYear;
    DevExpress.XtraEditors.Controls.LookUpColumnInfoCollection colInfo = lookupValues1.Properties.Columns;
    colInfo.Clear();
    colInfo.Add(new DevExpress.XtraEditors.Controls.LookUpColumnInfo("Column"));
    colInfo[0].Caption = "Values 1";
}

private async void form1_Load(object sender, EventArgs e)
{
    var tasks = new List<Task>();

    // Start each UI task so they will complete independently.
    var uiTask1 =  GetValues1()
          .ContinueWith(t =>
                LoadUIElements1(t.Result),
                CancellationToken.None,
                TaskCreationOptions.None,
                TaskScheduler.FromCurrentSynchronizationContext());
    tasks.Add(uiTask1);

    // Wait for all the tasks to complete
    Task.WaitAll(tasks.ToArray());
    tasks.Clear();
}