qt C++中鏈接Qline編輯組合框

Question

當我從組合框中選擇書籍編號時，我想將書名的值加載到文本框中。首先，我編寫了將Book Ids從數據庫加載到組合框的代碼，並且它完美加載。這是方法。

void FictionSection::loadComboVal() 
{ 
    DatabaseConnection mydb; 
    QSqlQueryModel *modl = new QSqlQueryModel(); 
    dbConOpen(); 

    QSqlQuery *query = new QSqlQuery(mydb.db) ; 
    query->prepare(" select material_id from fiction "); 
    bool flag = query->exec(); 

    //assigning the values to a QTableView 
    if(flag == true) 
    { 
     modl->setQuery(*query); 
     ui->cmbxId->setModel(modl); 

} 
    mydb.dbConClose(); 
} 

然後我寫的代碼分配值文本框一旦ID是從combobox.This選擇這本書是代碼段。

// loading book names once user select the book id from combo box 
void FictionSection::on_cmbxId_currentIndexChanged(int index) 
{ 
    QString value = ui->cmbxId->currentText(); 
    int id; 
    if(!value.isEmpty()) 
    { 
    id = value.toInt(); 
    } 
//Loading book table values to a table 

dbC onOpen(); 
     QSqlQuery query ; 
     QString ids = QString("values('") + QString::number(id); 
     query.prepare(" select material_title from book where material_id = '"+ids+"'"); 
    bool flag = query.exec(); 

    //assigning the values to a QTableView 
    if(flag == true) 
    { 
     ui->lneditFicNme->setText(query.value(1).toString()); 


    } 
    dbConClose(); 

} 

但隨後裝載值，組合框是不可見的，如我所料，我不能得到任何文本框的值。但沒有編譯或運行時錯誤。書本ID以數據庫中的varchar形式存儲爲int和書名。請幫我找到錯誤。先謝謝你。

我改變了代碼如下

void FictionSection::on_cmbxId_currentIndexChanged(int index) 
{ 
    QString value = ui->cmbxId->currentText(); 
    int id; 
    if(!value.isEmpty()) 
    { 
    id = value.toInt(); 
    } 
//Loading book table values to a table 

     dbConOpen(); 
     QSqlQuery query ; 
     // QString ids = QString("values('") + QString::number(id); 
     query.prepare(" select material_title from book where material_id = ?"); 
     query.bindValue(0,id); 
    bool flag = query.exec(); 

    //assigning the values to a QTableView 
    if(flag == true) 
    { 
     ui->lneditFicNme->setText(query.value(1).toString()); 


    } 
    else 
    { 

     QMessageBox :: critical(this,"Error",query.lastError().text()); 
    } 
    dbConClose(); 

} 

然後如下

QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work. 
QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed. 
QSqlQuery::value: not positioned on a valid record 
QSqlQuery::value: not positioned on a valid record 

我編輯了上面的代碼，但我仍然無法得到預期的結果給出了一個錯誤。

void FictionSection::on_cmbxId_currentIndexChanged(int index) 
{ 
    DatabaseConnection con; 
    con.dbConOpen(); 


    QString value = ui->cmbxId->currentText(); 
    int id; 
    if(!value.isEmpty()) 
    { 
    id = value.toInt(); 
    } 
//Loading book table values to a table 


     QSqlQuery query ; 

     // QString ids = QString("values('") + QString::number(id); 
     query.prepare(" select material_title from book where material_id = :id"); 
     query.bindValue(":id",id); 
    bool flag = query.exec(); 

    //assigning the values to a QTableView 
    if(flag == true) 
    { 

      while(query.next()) 
      { 

      ui->lneditFicNme->setText(query.value(1).toString()); 

      } 
    } 
    else 
    { 

     QMessageBox :: critical(this,"Error",query.lastError().text()); 
    } 
    con.dbConClose(); 
} 

請幫我解決這個問題。提前致謝

Answer 1

嘗試使用QSqlQuery::next()方法來定位有效記錄。