在表单之间传递值(winforms) [英] passing values between forms (winforms)

问题描述

将值传入和传出第二种形式时的奇怪行为.

Wierd behaviour when passing values to and from second form.

ParameterForm pf = new ParameterForm(testString);

作品

ParameterForm pf = new ParameterForm();
pf.testString="test";

没有(testString 定义为公共字符串)

doesn't (testString defined as public string)

也许我错过了什么?无论如何，我想让第二个变体正常工作，就目前而言 - 它返回空对象引用错误.

maybe i'm missing something? Anyway I'd like to make 2nd variant work properly, as for now - it returns null object reference error.

感谢您的帮助.

在此处发布更多代码:

打电话

Button ParametersButton = new Button();
ParametersButton.Click += delegate
                {
                    ParameterForm pf = new ParameterForm(doc.GetElementById(ParametersButton.Tag.ToString()));
                    pf.ShowDialog(this);
                    pf.test = "test";
                    pf.Submit += new ParameterForm.ParameterSubmitResult(pf_Submit);
                };

定义和使用

   public partial class ParameterForm : Form
    {
        public string test;
        public XmlElement node;
        public delegate void ParameterSubmitResult(object sender, XmlElement e);
        public event ParameterSubmitResult Submit;

        public void SubmitButton_Click(object sender, EventArgs e)
        {
            Submit(this,this.node);
            Debug.WriteLine(test);
        }
     }

结果:提交 - 空对象引用测试 - 空对象引用

result: Submit - null object reference test - null object reference

推荐答案

• pf.ShowDialog(this); 是一个阻塞调用，所以 pf.Submit += new ParameterForm.ParameterSubmitResult(pf_Submit); 永远不会到达:切换顺序.

  • pf.ShowDialog(this); is a blocking call, so pf.Submit += new ParameterForm.ParameterSubmitResult(pf_Submit); is never reached: switch the order.

    Submit(this,this.node); 抛出一个空对象引用，因为没有事件分配给它(见上文).通常，您应该始终首先检查:if (Submit != null) Submit(this,this.node);

    Submit(this,this.node); throws a null object reference because no event is assigned to it (see above). Generally, you should always check first: if (Submit != null) Submit(this,this.node);

    你应该改变``pf.ShowDialog(this); topf.Show(this);`，这样你的主窗体就不会在你的对话框打开时被禁用，如果这就是你想要的，或者使用下面的模型(典型的对话框.)

    You should change ``pf.ShowDialog(this);topf.Show(this);` so that your main form isn't disabled while your dialog box is open, if that's what you want, or use the model below (typical for dialog boxes.)

    我不确定 pf_Submit 应该做什么，所以这可能不是在您的应用程序中处理它的最佳方法，但它是继续?是/否"问题的一般性问题工作.

    I'm not sure what pf_Submit is supposed to do, so this might not be the best way to go about it in your application, but it's how general "Proceed? Yes/No" questions work.

    Button ParametersButton = new Button();
    ParametersButton.Click += delegate
        {
            ParameterForm pf = new ParameterForm(testString);
            pf.ShowDialog(this); // Blocks until user submits
            // Do whatever pf_Submit did here.
        };
    
    public partial class ParameterForm : Form
    {
        public string test;     // Generally, encapsulate these
        public XmlElement node; // in properties
    
        public void SubmitButton_Click(object sender, EventArgs e)
        {
            Debug.WriteLine(test);
            this.Close(); // Returns from ShowDialog()
        }
     }
    

    这篇关于在表单之间传递值(winforms)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！