清除 ListView (firemonkey)

Question

我正在为具有按钮和 TListView 控件的 Windows 构建 FMX 应用程序。按钮代码只是用于填充 TListView 的 SQLite 数据库的查询。在某些情况下，查询需要 5-10 秒来处理。我想在单击按钮时立即清除 TListView（在查询完成并重新填充列表之前）。在第一个按钮代码中，我调用了 Clear 方法，但它不能立即工作：

ListView1->Clear();

旧数据保留在 TListView 控件中，直到查询完成并刷新它。如何强制列表为空 FIRST。

谢谢， 罗斯

已更新以清楚地显示正在发生的事情：

// This entire block of code below is inside a button click.
Form1->ListView1->Clear();
// This next line of code is what Frederico suggested - it works.
Application->ProcessMessages();

Form1->FDConnection1->Params->Values["Database"] = "T:\\mydata.db";
TFDQuery *query;
query = new TFDQuery(NULL);
query->Connection = Form1->FDConnection1;    // SQLite db
query->SQL->Text = "SELECT DISTINCT Project FROM Engineer_Updates WHERE Employee = '" + Form1->lblEngineerInitials->Text + "' ORDER BY Project";
query->Open();
  while(!query->Eof) {
    TListViewItem* itemHeader = Form1->ListView1->Items->Add();
    Form1->ListView1->BeginUpdate();
    itemHeader->Purpose = TListItemPurpose::Header;
    itemHeader->Text = query->FieldByName("Project")->AsString; // + " - " + query->FieldByName("Project WO")->AsString;  // "My Header";
    Form1->ListView1->EndUpdate();
        TFDQuery *query2;
        query2 = new TFDQuery(NULL);
            try {
            query2->Connection = Form1->FDConnection2;    // SQLite db
            query2->SQL->Text = "SELECT * FROM Engineer_Updates WHERE Project = '" + query->FieldByName("Project")->AsString + "' AND Employee = '" + Form1->lblEngineerInitials->Text + "'";
            query2->Open();
                 while (!query2->Eof) {
                  TListViewItem* item2Add = Form1->ListView1->Items->Add();
                  Form1->ListView1->BeginUpdate();
                  item2Add->Text = query2->FieldByName("Terminal/Equipment")->AsString + ", " + query2->FieldByName("Activity")->AsString;
                  mystring2 = query2->FieldByName("Terminal/Equipment")->AsString + ", " + query2->FieldByName("Activity")->AsString;
                  item2Add->Detail = mystring2;
                  Form1->ListView1->EndUpdate();
                  query2->Next();
                }
            }
            __finally {
              query2->Close();
              query2->DisposeOf();
            }
    query->Next();
    }
    query->Close();
    query->DisposeOf();

Answer 1

一种可能的解决方案（使用 Delphi 代码）：

ListView1.Clear;
//eventually show a spinning wheel here, so the user knows something is going on.
ListView1.InvalidateRect(ListView1.BoundsRect); //<- might not be needed, try first without
TThread.ForceQueue(nil, procedure
  begin
    //execute your query here and fill the listview
    //stop the spinning wheel
  end;

Answer 2

TListView 是否通过 BindSource 绑定？如果是，请尝试使用单独的线程清除数据，例如匿名线程并禁用 bindsource 中的数据集

BindSourceDB1.DataSet.Active := False;
TThread.CreateAnonymousThread(procedure ()
begin
    // delete data here using separated query
    TThread.Synchronize(nil, procedue ()
    begin
        BindSourceDB1.DataSet.Active := True;
    end);
end).Start;