访问列表中包含的对象的特定属性 <Object> 在C＃中

Question

I can't seem to figure out how to access specific properties of each object contained within a list. For example, if I reference the object outside of the list (prior to passing it to the button click), I can see properties like "tag", "height", "width", etc. (all the standard properties for that type). However, I cannot figure out how to access those object-specific properties once the list has been passed to my button click event.

Please refer to this example:

private TextBox createTextBox(string name)
{
    // Create TextBox Code is Here
    TextBox dTextBox = new TextBox();
    dTextBox.Name = name;
    dTextBox.Tag = "sometag";
    dTextBox.Height = 12345;
    dTextBox.Width = 12345;
    return dTextBox;
}

private void some_function()
{
    var objectList = new List<Object>();
    objectList.Add(createTextBox("example1"));
    objectList.Add(createTextBox("example2"));
    objectList.Add(createTextBox("example3"));
}

private int button_click(object sender, EventArgs e, Int32 ticketGroupID, List<Object> objectList)
{
    for(int i = 0; i < objectList.Count(); i++)
    {
        Int32 valuableInfo = objectList[i].?? // Here is where I am trying to access specific properties about the object at index i in the list, such as the objects TAG, VALUE, etc. How can this be done?
        // do things with the valuable info
    };

}

Thanks in advance for any assistance.

Answer 1

You need to make the object strongly-typed. That is, to cast it to your class :

Int32 valuableInfo = ((TextBox)objectList[i]).Height; //now you can access your property

Otherwise, you cannot access the properties of the class because the compiler wouldn't know what is the actual type of the object . Also, your Intellisense will just deemed it as object , not your strongly-typed class (example: MyClass , or in your case, the class being TextBox )

Answer 2

It's a List<> which implements IEnumerable<T> , so you can make use of the OfType<T>() method to extract items that are already strongly typed and ready for you to access:

var myListOfTypedObjects = myList.OfType<TextBox>();
myListOfTypedObjects.ForEach(tb => Console.Writeline(tb.Name));

Answer 3

You can either check type first, then cast it to TextBox later or reverse .

See example below:

foreach (var obj in objectList)
{
    // method 1: check first, cast later
    if (obj is TextBox)
    {
        Int32 valueableInfo = ((TextBox)obj).Height;
    }

    // method2: cast first, check later
    var textBox = obj as TextBox;
    if (obj != null)
    {
        Int32 valueableInfo = obj.Height;
    }
}