ComboBox.SelectedValue returns System.Data.DataRowView

Question

错误是'从对象类型system.data.data.datarowview到已知的托管提供商本机类型。现在comBoxMuscleGroup.SelectedValue和comBoxTypeFitness.SelectedValue应该返回ID，而是返回'System.Data.DatarowView'。有人可以帮我吗？

代码：

       private void TypeFitness()
       {
           string query = "SELECT Naam FROM TypeFitness";
           using (connection = new SqlConnection(connectionString))
           using (SqlDataAdapter adapter = new SqlDataAdapter(query, connection))
           {
               DataTable data = new DataTable();
               adapter.Fill(data);
               comBoxTypeFitness.DisplayMember = "Naam";
               comBoxTypeFitness.ValueMember = "FitnessId";
               comBoxTypeFitness.DataSource = data;
           }
       }
       private void MuscleGroup()
       {
           string query = "SELECT Naam FROM MuscleGroup";
           using (connection = new SqlConnection(connectionString))
           using (SqlDataAdapter adapter = new SqlDataAdapter(query, connection))
           {
               DataTable data = new DataTable();
               adapter.Fill(data);
               comBoxMuscleGroup.DisplayMember = "Naam";
               comBoxMuscleGroup.ValueMember = "MuscleId";
               comBoxMuscleGroup.DataSource = data;
           }
       }
       private void Exercises()
       {
           string query = "SELECT Naam FROM Xercises AS X " +
               "INNER JOIN MG_Exercise AS MGX ON MGX.ExerciseId = X.ExerciseId " +
               "WHERE MGX.MuscleId = @MuscleId AND X.FitnessId = @FitnessId";
           using (connection = new SqlConnection(connectionString))
           using (SqlCommand command = new SqlCommand(query, connection))
           using (SqlDataAdapter adapter = new SqlDataAdapter(command))
           {
               //int MuscleId = ((DataRowView)comBoxMuscleGroup.SelectedValue).Row.Field<int>("MuscleId");
            //int FitnessId = ((DataRowView)comBoxTypeFitness.SelectedValue).Row.Field<int>("FitnessId");
               command.Parameters.AddWithValue("@MuscleId", comBoxMuscleGroup.SelectedValue);
               command.Parameters.AddWithValue("@FitnessId", comBoxTypeFitness.SelectedValue);
               DataTable data = new DataTable();
               adapter.Fill(data);
               clbXcercises.DisplayMember = "Naam";
               clbXcercises.ValueMember = "ExerciseId";
               clbXcercises.DataSource = data;
           }
       }

Answer 1

属性valuemember和displaymember是两个字符串，应该是两个字段的名称，可提供来自数据源的值。
您的查询不包含您为组合的命名为ValueMember的字段。
因此，它不可能在属性中给出精确的值，而只是用于在组合内构建一行的类的名称（dataRowView）

如果要将所选值设置为当前选定项目的MuscleID或FitnessID值，则需要从数据库中提取这些值。

您需要将查询更改为

string query = "SELECT FitnessID, Naam FROM TypeFitness";

和

string query = "SELECT MuscleID, Naam FROM MuscleGroup";

最终查询还需要进行练习

  string query = "SELECT ExerciseID, Naam FROM Xercises AS X " +
       "INNER JOIN MG_Exercise AS MGX ON MGX.ExerciseId = X.ExerciseId " +
       "WHERE MGX.MuscleId = @MuscleId AND X.FitnessId = @FitnessId";

我还建议在使用之前始终检查针对所选价值属性的空。