AsyncTasks和ProgressDialogs

Question

我需要使用服务器中的数据列表构建BaseExpandableListAdapters。我正在使用AsyncTask来检索这个值列表。由于我目前无法从DoInBackGround覆盖方法返回BaseExpandableListAdapter，因此我使用的是公共属性。使用以下代码我可以：

1. 获取我的AsyncTask类的My和Market属性以返回所有预期值但是我的ProgressDialog在执行任务之后才会出现，使其无用，或者
2. 根据需要立即显示ProgressDialog但是当我尝试使用它们将适配器分配给我的列表视图时，My和Market属性为空

我需要实现两者。

public class Work : Activity
{
    private ExpandableListView market;
    private ExpandableListView my;

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        SetContentView(Resource.Layout.Work);

        market = (ExpandableListView)FindViewById(Resource.Id.market);
        my = (ExpandableListView)FindViewById(Resource.Id.my);

        PopulateWorkListViews populate = new PopulateWorkListViews(this);
        populate.Execute(techID, market, userType);

        //Removing the following line allows for the ProgressDialog but the Market 
        //and My properties of the PopulateWorkListViews class are empty as opposed 
        //to leaving this line in and both properties contain all expected values 
        //but ProgressDialog doesn't show up.
        string result = populate.Get().ToString();

        market.SetAdapter(populate.Market);
        my.SetAdapter(populate.My);
    }
}

public class PopulateWorkListViews : AsyncTask
{
    private Context Context { get; set; }
    private ProgressDialog Dialog { get; set; }
    public BaseExpandableListAdapter Market { get; set; }
    public BaseExpandableListAdapter My { get; set; }

    public PopulateWorkListViews(Context context)
    {
        Context = context;
    }

    protected override void OnPreExecute()
    {
        Dialog = new ProgressDialog(Context);
        Dialog.SetMessage("Processing...");
        Dialog.Window.SetGravity(GravityFlags.Center);
        Dialog.SetCancelable(false);
        Dialog.Indeterminate = true;
        Dialog.SetProgressStyle(ProgressDialogStyle.Spinner);
        Dialog.Show();
    }

    protected override Java.Lang.Object DoInBackground(params Java.Lang.Object[] @params)
    {
        WS ws = new WS();
        List<ServiceCall> calls = ws.GetMarketCalls(@params[0].ToString(), @params[1].ToString(), @params[2].ToString()).ToList();

        Market = new MarketCallListView(Context, calls);
        My = new MyCallListView(Context, calls, @params[0].ToString());

        return "Done";
    }

    protected override void OnPostExecute(Java.Lang.Object result)
    {
        Dialog.Dismiss();
    }
}

Answer 1

不立即绘制对话框的原因是您在populate.Get()中阻止了UI线程。如果您将SetAdapter底部的两条onCreate行移至onPostExecute，该怎么办？