c# – 设置属性值时的NullReferenceException
发布时间:2020-12-15 20:51:59 所属栏目:百科 来源:网络整理
导读:using System;using System.Collections.Generic;using System.ComponentModel;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ConsoleApplication3{ class Cls : INotifyPropertyChanged { private string my; public string
using System; using System.Collections.Generic; using System.ComponentModel; using System.Linq; using System.Text; using System.Threading.Tasks; namespace ConsoleApplication3 { class Cls : INotifyPropertyChanged { private string my; public string MyProperty { get { return my; } set { my = value; PropertyChanged(this,new PropertyChangedEventArgs("MyProperty")); } } public Cls() { MyProperty = "Hello"; } public void print() { Console.WriteLine(MyProperty); } protected virtual void OnPropertyChanged(string name) { } public event PropertyChangedEventHandler PropertyChanged; } class Program { static void Main(string[] args) { Cls s = new Cls(); s.print(); } } } 当我运行此代码时,它给出:
当我不使用INotifyPropertyChanged它工作正常.我不明白问题的原因. 解决方法
没有人会收听??PropertyChanged,在尝试调用它时它将为null.改为使用OnPropertyChanged方法:
private void OnPropertyChanged(string propertyName){ var handler = PropertyChanged; if (handler != null) handler(this,new PropertyChangedEventArgs(propertyName)); // With C# 6 this can be replaced with PropertyChanged?.Invoke(this,new PropertyChangedEventArgs(propertyName)); } public string MyProperty { get { return my; } set { if (my == value) return; my = value; OnPropertyChanged("MyProperty"); } } 要避免它为null,您必须订阅它,例如从您的main方法: static void Main(string[] args){ Cls s = new Cls(); s.PropertyChanged += (sender,args) => MessageBox.Show("MyProperty changed!"); s.print(); } 这是一种奇特的写作方式 static void Main(string[] args){ Cls s = new Cls(); s.PropertyChanged += ShowMessage; s.print(); } private void ShowMessage(object sender,PropertyChangedEventArgs args){ MessageBox.Show("MyProperty changed!"); } 无论你怎么说都清楚. (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |