Question

我正在为Windows构建一个FMX应用程序，该应用程序具有一个按钮和一个TListView控件。按钮代码只是对用于填充TListView的SQLite数据库的查询。在某些情况下，查询需要5到10秒钟来处理。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）。在按钮代码的第一个中，我调用了Clear方法，但无法立即使用：

ListView1->Clear();

旧数据将保留在TListView控件中，直到查询完成并刷新它。我如何强制列表首先清空。

谢谢，鲁斯

已更新以清楚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

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绑定了？如果是，请尝试使用单独的线程（例如匿名线程）清除数据并禁用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;

清除ListView（firemonkey）

2 个答案: