Question

我有以下代码（这是我试图在其中包含所有重要信息的摘录）

public partial class MyTopScreen : Form
{
    public bool _myVariable ;
    public CommonForm _commonGridForm;
    public MyTopScreen(bool first_param, string second_param )
    {           
        CommonForm commonGridForm = new CommonForm();
        DataGridView dataGridView1 = commonGridForm.dataGridView1;
        _commonAttributForm = commonAttributForm;          
        InitializeComponent();
        this.TabPage1.Controls.Add(dataGridView1);
    }  
 }

然后当我在CommonForm内时，如下所示：

public partial class CommonForm : Form        
{
    public CommonForm()
    {
        //My Question is how do I access the _myVariable from this point in the code ?
        //this.parent      doesnot work or does not give me access to _myVaribale
    }
 }

提前感谢您的帮助。

Answer 1

您必须将父级转换为适当的类型：

MyTopScreen myParent = this.parent as MyTopScreen;
if (myParent != null)
{
    bool myVariableFromParent = myParent._myVariable;
}

只有小心转换，因为如果父级是不同的控件，那么在尝试访问_myVariable时，您将获得空引用异常。另外，不要尝试直接强制转换（(MyTopScreen)this.parent），因为如果父级是不同的控件，您将获得强制转换异常。

Answer 2

一种方法是将MyTopScreen的实例传递给其他类＆＃39;构造函数，如果它与它有关。将它存放在一个字段中。

public partial class CommonForm : Form
{
    public CommonForm(MyTopScreen screen)
    {
        this.TopScreen = screen;
    }

    private MyTopScreen TopScreen{ get; set; }
}

现在，您可以通过CommonForm

在TopScreen._myVariable.中访问该变量了

你必须将它传递给构造函数：

CommonForm commonGridForm = new CommonForm(this);

Answer 3

this.Parent不起作用的原因是因为您从未将MyTopScreen设置为父级。您需要在代码中添加commonGridForm.Parent = this。然后你可以拨打((MyTopScreen) this.Parent)._myVariable。但这只是为了让您当前的代码正常工作;它肯定是不是最好的方法。

我建议的一个改进是不公开公开您的字段，而是将它们用作通过属性公开的支持字段（请参阅this）。

此外，您可以通过构造函数将对父窗体的引用传递给子窗体。以下是您的代码的样子：

public partial class MyTopScreen : Form
{
    //keep your fields private.

    private bool _myVariable;
    private CommonForm _commonGridForm;

    //expose fields through properties.

    public bool MyVariable
    {
        get { return _myVariable; }
    }

    public CommonForm CommonGridForm
    {
        get { return _commonGridForm; }
    }

    public MyTopScreen(bool first_param, string second_param)
    {
        CommonForm commonGridForm = new CommonForm(this);
        DataGridView dataGridView1 = commonGridForm.dataGridView1;
        _commonAttributForm = commonAttributForm;          
        InitializeComponent();
        this.TabPage1.Controls.Add(dataGridView1);

    }
}


public partial class CommonForm : Form
{
    private MyTopScreen _parent;

    //inject parent reference in child form's constructor.

    public CommonForm(MyTopScreen withParent)
    {
        _parent = withParent;
        //_parent.MyVariable <-- here's how you'd access your var.
    }
}

Answer 4

创建CommonForm类的参数化构造函数（Constructor Overloading）并将bool值传递给它。

public partial class MyTopScreen : Form
{
    public bool _myVariable ;
    public CommonForm _commonGridForm;
    public MyTopScreen(bool first_param, string second_param )
    {           
        CommonForm commonGridForm = new CommonForm(_myVariable);
        DataGridView dataGridView1 = commonGridForm.dataGridView1;
        _commonAttributForm = commonAttributForm;          
        InitializeComponent();
        this.TabPage1.Controls.Add(dataGridView1);

    }  
 } 

public partial class CommonForm : Form
{
        public CommonForm(bool _myVariable)
        {
           //Here you access the variable
        }
 }

Answer 5

有几种方法可以做到这一点。如果值不会改变，您可以将其传递给CommonForm的构造函数（推荐）：

public partial class CommonForm : Form
{
    public CommonForm(bool myVariable)
    {
       // available
    }
}

CommonForm commonGridForm = new CommonForm(_myVariable);

如果它可以更改，您可以将实例传递给构造函数中的父窗体：

public partial class CommonForm : Form
{
    public CommonForm(MyTopScreen parent)
    {
       // available
       parent._myVariable;
    }
}

CommonForm commonGridForm = new CommonForm(this);

如何从添加到另一个控件的子控件访问变量？

5 个答案: