Question

ObjectCollection.Add（item）是否调用item.Equals（）？在CheckedListBox上找到了Form，并尝试添加一些项目。但是我发现调用CheckedListBox.Items.Add(item)时会调用item.Equals()。另外，我发现item.GetHashCode()也被调用了。对于为什么会发生感到非常困惑。代码如下。

List<Person> people = new List<Person>();//Person is a customer class for test.
people.Add(new Person() { Name = "张三", Id = "201411580572", Gender = "Male" });
people.Add(new Person() { Name = "李四", Id = "201411580573", Gender = "Male" });
people.Add(new Person() { Name = "王武", Id = "201411580574", Gender = "Male" });
people.Add(new Person() { Name = "赵柳", Id = "201411580575", Gender = "Male" });
people.Add(new Person() { Name = "张飞", Id = "201411580576", Gender = "Male" });
people.Add(new Person() { Name = "赵云", Id = "201411580577", Gender = "Male" });

cklTest.DisplayMember = "Name";//cklTest is a CheckedListBox.

people.ForEach(p => cklTest.Items.Add(p));

修改：

callstack

Answer 1

您的呼叫堆栈显示该呼叫来自Formatter.FormatObject，后者依次呼叫Formatter.IsNullData。

The code of IsNullData是：

public static bool IsNullData(object value, object dataSourceNullValue) {
    return value == null ||
           value == System.DBNull.Value ||
           Object.Equals(value, NullData(value.GetType(), dataSourceNullValue));
}

我们看到了对Object.Equals的调用，以检查您的对象是否等于dataSourceNullValue（代表空数据的自定义值）。有趣的是，在这种情况下dataSourceNullValue为DBNull.Value，因此上述检查是多余的。但是您对此无能为力。

如果您不希望在此代码路径上调用Equals，则可以通过将FormattingEnabled设置为false来解决。这将导致CheckedListBox使用an alternative way格式化对象：

if (!formattingEnabled) {

    // Microsoft gave his blessing to this RTM breaking change
    if (item == null) {
        return String.Empty;
    }

    item = FilterItemOnProperty(item, displayMember.BindingField);
    return (item != null) ? Convert.ToString(item, CultureInfo.CurrentCulture) : "";
}

ObjectCollection.Add（）如何工作

1 个答案: