Question

我创建了一个带数据绑定的简单示例（遗憾的是我们的系统中有类似的情况）。我创建了一个时髦的组合框：

public class FunkyComboBox : ComboBox
{
    private object currentValue = null;

    public FunkyComboBox()
    {
        if (LicenseManager.UsageMode == LicenseUsageMode.Runtime)
            this.Items.Add("Other...");
    }

    protected override void OnSelectedIndexChanged(EventArgs e)
    {
        if (!this.Text.StartsWith("Other") && currentValue != this.SelectedItem)
        {
            currentValue = this.SelectedItem;
            BindingManagerBase bindingManager = DataManager;
            base.OnSelectedIndexChanged(e);
        }
    }

    protected override void OnSelectionChangeCommitted(EventArgs e)
    {
        string itemAsStr = this.SelectedItem != null ? SelectedItem.ToString() : "";
        if (itemAsStr.StartsWith("Other"))
        {
            string newItem = "item" + this.Items.Count;
            if (!Items.Contains(newItem))
            {
                Items.Add(newItem);
            }
            SelectedItem = newItem;
        }
        else
        {
            OnSelectedIndexChanged(e); //forces a selectedIndexChanged event to be thrown
            base.OnSelectionChangeCommitted(e);
        }
    }
}

当您单击其他时，会添加新项目（在我们的系统中，它会打开一个可以查询数据库的表单等）。然后我有一个简单的数据对象：

public class MyClass
{
    private string value;
    public string MyData
    {
        get{ return value;}
        set{ this.value = value;}
    }
}

一个带有两个控件的测试表单绑定到此对象（删除了一些设计器代码）：

public partial class Form1 : Form
{
    MyClass myObj = new MyClass();
    public Form1()
    {
        InitializeComponent();
        myObj.MyData = "Nothing";
        myClassBindingSource.DataSource = myObj;
    }

    private void InitializeComponent()
    {
        this.components = new System.ComponentModel.Container();
        this.textBox1 = new System.Windows.Forms.TextBox();
        this.myClassBindingSource = new System.Windows.Forms.BindingSource(this.components);
        this.funkyComboBox1 = new DataBindingTests.FunkyComboBox();
        ((System.ComponentModel.ISupportInitialize)(this.myClassBindingSource)).BeginInit();
        this.SuspendLayout();
        //
        // textBox1
        //
        this.textBox1.DataBindings.Add(new System.Windows.Forms.Binding("Text", this.myClassBindingSource, "MyData", true, System.Windows.Forms.DataSourceUpdateMode.OnPropertyChanged));

        //
        // myClassBindingSource
        //
        this.myClassBindingSource.DataSource = typeof(DataBindingTests.MyClass);
        //
        // funkyComboBox1
        //
        this.funkyComboBox1.DataBindings.Add(new System.Windows.Forms.Binding("SelectedItem", this.myClassBindingSource, "MyData", true, System.Windows.Forms.DataSourceUpdateMode.OnPropertyChanged));
        this.funkyComboBox1.DataBindings.Add(new System.Windows.Forms.Binding("SelectedValue", this.myClassBindingSource, "MyData", true, System.Windows.Forms.DataSourceUpdateMode.OnPropertyChanged));
        //
        // Form1
        //
        this.Controls.Add(this.textBox1);
        this.Controls.Add(this.funkyComboBox1);
        ((System.ComponentModel.ISupportInitialize)(this.myClassBindingSource)).EndInit();
        this.ResumeLayout(false);
        this.PerformLayout();
    }

    private FunkyComboBox funkyComboBox1;
    private System.Windows.Forms.BindingSource myClassBindingSource;
    private System.Windows.Forms.TextBox textBox1;
}

如果您运行此代码并开始使用组合框，您会注意到编辑框只有在您单击它时才会更改。每次更改后，都会将空值设置为我的对象，并清除文本框。如何在每次更改后设置正确的值？

Answer 1

我不确定为什么ComboBox数据绑定会以这种方式运行，但我找到了一种解决方法。如果您没有为ComboBox的值使用数据源，似乎数据绑定无法正常工作。

我对FunkyComboBox做了一些小改动，现在按预期工作了。

public class FunkyComboBox : ComboBox
{
    private object currentValue = null;
    private List<string> innerItems = new List<string>();

    public FunkyComboBox()
    {
        if (LicenseManager.UsageMode == LicenseUsageMode.Runtime)
            innerItems.Add("Other...");

        this.DataSource = innerItems;
    }

    protected override void OnSelectedIndexChanged(EventArgs e)
    {
        if (!this.Text.StartsWith("Other") && currentValue != this.SelectedItem)
        {
            currentValue = this.SelectedItem;
            BindingManagerBase bindingManager = DataManager;
            base.OnSelectedIndexChanged(e);
        }
    }

    protected override void OnSelectionChangeCommitted(EventArgs e)
    {
        string itemAsStr = this.SelectedItem != null ? SelectedItem.ToString() : "";
        if (itemAsStr.StartsWith("Other"))
        {
            string newItem = "item" + this.Items.Count;                
            if(!innerItems.Contains(newItem))
            {
                innerItems.Add(newItem);
                this.RefreshItems();
            } SelectedItem = newItem;
        }
        else
        {
            OnSelectedIndexChanged(e);
            //forces a selectedIndexChanged event to be thrown              
            base.OnSelectionChangeCommitted(e);
        }
    }
}

Answer 2

它似乎也是基本ComboBox的一个错误。不可能使这种绑定源疯狂正常工作。

数据绑定不更新

2 个答案: