Question

我有一个窗口表单，involes填写带有信息的文本框，然后单击连接。如果任何文本框都为空，我会弹出错误消息但是当我点击OK时程序就会继续，我最终得到运行时错误，因为信息不足，程序崩溃了。我想要的是，只要没有正确填写任何文本框，程序就会在我点击“连接”之前回到这一点。

这是代码：

private void cmdConnect_Click(object sender, EventArgs e)
    {

        if (cmdConnect.Text == "Connect")
        {
            if (txtGroup.Text == "")
            {
                txtGroup.Text = "_Group01";
            }

            if (txtItemID.Text == "")
            {
                MessageBox.Show("Please enter ItemID.", "Connect Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

            }
                switch (cboServer.Text)
                {
                    case "":
                        MessageBox.Show("Please select and OPC server", "Connect Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                        break;


                    case "RSLinx Remote OPC Server":
                        if (txtMachine.Text == "")
                        {
                            MessageBox.Show("Please enter a machine name for remote connection", "Connect Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                            break;
                        }
                        else
                        {
                            oOpcServer.Connect(cboServer.Text, txtMachine.Text);
                        }
                        break;

                    case "RSLinx OPC Server":
                        oOpcServer.Connect(cboServer.Text);
                        break;

                    default:
                        if (txtMachine.Text == "")
                        {
                            oOpcServer.Connect(cboServer.Text);
                        }
                        else
                        {
                            oOpcServer.Connect(cboServer.Text, txtMachine.Text);


                        }
                        break;
            }
            oOpcGroup = oOpcServer.OPCGroups.Add(txtGroup.Text);
            oOpcGroup.IsSubscribed = true;
            oOpcGroup.IsActive = false;
            oOpcGroup.UpdateRate = 1000;


            ClHandle = 1;
            oOpcGroup.OPCItems.DefaultAccessPath = txtAccessPath.Text;
            oOpcGroup.OPCItems.AddItem(txtItemID.Text, ClHandle);

            cmdItemWrite.Enabled = true;
            cmdItemRead.Enabled = true;
            cmdSyncWrite.Enabled = true;
            cmdSyncRead.Enabled = true;
            cmdAsyncWrite.Enabled = true;
            cmdAsyncRead.Enabled = true;
            cmdAdvise.Enabled = true;
            txtSubValue.Enabled = true;
            cboServer.Enabled = false;
            txtMachine.Enabled = false;
            txtGroup.Enabled = false;
            txtAccessPath.Enabled = false;
            txtItemID.Enabled = false;

            cmdConnect.Text = "Disconnect";
        }
        else
        {
            oOpcServer.OPCGroups.RemoveAll();
            oOpcGroup = null;
            oOpcServer.Disconnect();

            cmdConnect.Text = "Connect";
            cmdItemWrite.Enabled = false;
            cmdItemRead.Enabled = false;
            cmdSyncWrite.Enabled = false;
            cmdSyncRead.Enabled = false;
            cmdAsyncWrite.Enabled = false;
            cmdAsyncRead.Enabled = false;
            cmdAdvise.Enabled = false;
            txtSubValue.Enabled = false;
            cboServer.Enabled = true;
            txtMachine.Enabled = true;
            txtGroup.Enabled = true;
            txtAccessPath.Enabled = true;
            txtItemID.Enabled = true;
        }
        oOpcGroup.DataChange += new RsiOPCAuto.DIOPCGroupEvent_DataChangeEventHandler(oOpcGroup_DataChange);
    }

Answer 1

在每个消息框之后添加return语句可以解决问题，并导致方法退出而不进行最后的工作。

Answer 2

最简单的解决方案，正如Dervall所提到的，是在每次return调用后添加MessageBox.Show语句。但更优雅的解决方案是在执行连接逻辑之前使用验证和错误提供程序突出显示错误的输入数据。

无论如何，这里有一些关于重构代码的想法。

private void cmdConnect_Click(object sender, EventArgs e)
{
    if (cmdConnect.Text == "Disconnect") 
    {
        Disconnect();
        SetControlsToDisconnectedState();
        return;
    }

    if (String.IsNullOrWhiteSpace(txtGroup.Text))
        txtGroup.Text = "_Group01";


    if (String.IsNullOrWhiteSpace(txtItemID.Text))
    {
        ShowErrorMessage("Connect Error", "Please enter ItemID.");
        return;
    }

    if (String.IsNullOrWhiteSpace(cboServer.Text))
    {
        ShowErrorMessage("Connect Error", "Please select and OPC server");
        return;
    }

    Connect(cboServer.Text, txtMachine.Text);
    DoSomethingWithGroup(txtGroup.Text, txtAccessPath.Text, txtItemID.Text);
    SetControlsToConnectedState();
}

发生了什么变化：

当您验证按钮上的哪个文本，然后它没有
方法ShowErrorMessage正如它所说的那样
使用IsNullOrWhiteSpace验证文字，因为它可能包含空格
控制状态更改已移至单独代码
现在连接/断开与UI分离

这里有其他方法：

private void ShowErrorMessage(string title, string message)
{
    MessageBox.Show(message, title, MessageBoxButtons.OK, MessageBoxIcon.Error);
}

private void SetControlsToConnectedState()
{
    UpdateControls(true);
}

private void SetControlsToDisconnectedState()
{
    UpdateControls(false);
}

private void UpdateControls(bool isConnected)
{
    cmdConnect.Text = isConnected ? "Disconnect" : "Connect";
    cmdItemWrite.Enabled = isConnected;
    cmdItemRead.Enabled = isConnected;
    cmdSyncWrite.Enabled = isConnected;
    cmdSyncRead.Enabled = isConnected;
    cmdAsyncWrite.Enabled = isConnected;
    cmdAsyncRead.Enabled = isConnected;
    cmdAdvise.Enabled = isConnected;
    txtSubValue.Enabled = isConnected;
    cboServer.Enabled = !isConnected;
    txtMachine.Enabled = !isConnected;
    txtGroup.Enabled = !isConnected;
    txtAccessPath.Enabled = !isConnected;
    txtItemID.Enabled = !isConnected;      
}

private void Disconnect()
{
    oOpcServer.OPCGroups.RemoveAll();
    oOpcGroup = null;
    oOpcServer.Disconnect();            
}

private void Connect(string serverName, string machineName)
{
    switch (serverName)
    {
        case "RSLinx Remote OPC Server":
            if (String.IsNullOrWhiteSpace(machineName))
            {
                ShowErrorMessage("Connect Error", "Please enter a machine name for remote connection");
                return;
            }

            oOpcServer.Connect(serverName, machineName);                    
            break;

        case "RSLinx OPC Server":
            oOpcServer.Connect(serverName);
            break;

        default:
            if (String.IsNullOrWhiteSpace(machineName))            
                oOpcServer.Connect(serverName);            
            else            
                oOpcServer.Connect(serverName, machineName);            
            break;
    }           
}

private void DoSomethingWithGroup(string groupName, string accessPath, string itemID)
{
    oOpcGroup = oOpcServer.OPCGroups.Add(groupName);
    oOpcGroup.IsSubscribed = true;
    oOpcGroup.IsActive = false;
    oOpcGroup.UpdateRate = 1000;

    ClHandle = 1;
    oOpcGroup.OPCItems.DefaultAccessPath = accessPath;
    oOpcGroup.OPCItems.AddItem(itemID, ClHandle);

    oOpcGroup.DataChange += new RsiOPCAuto.DIOPCGroupEvent_DataChangeEventHandler(oOpcGroup_DataChange);
}

在按钮内处理错误

2 个答案: