C# 属性和字段

不将理论，直接看不同的代码产生什么样的影响

下面代码中有字段和其对应的属性：

 private string title;

 public string Title ...

通过做实验可知，当我给属性赋值，即Title="News";此时如果单步调试，会进入到属性的set代码段中，而且如果我们一直关注title和Title的值，可以发现，只有当title = value;这句话成功执行之后，title和Title才会一起变成新的值。也就是说只有当字段title被成功赋值，属性Title才会跟被赋值。如果我们执行代码段2，由于if(true)，使得title = value;没有得到执行，我们可以看到，最终的结果是title和Title都没有变，还是原来的老值。或者不执行代码段2，当老值和新值相同的时候，也能忽略掉title=value;

代码段1：

        private string title;

        public string Title
        {
            get { return title; }
            //set { Set(ref title, value); }
            set
            {
                if (title == value) { return; }
                title = value;
                RaisePropertyChanged(() => Title);
            }
        }    

代码段2

        private string title;

        public string Title
        {
            get { return title; }
            //set { Set(ref title, value); }
            set
            {
                if (title == value) { return; }
                if (true)
                {
                    return;
                }
                title = value;
                RaisePropertyChanged(() => Title);
            }
        }

如果我们如果给字段(private)赋值，即title="news"，此时是不会进入到属性Title的set代码段的。而且执行完成之后，属性Title和字段title，会同时被赋予新值"news"。

前台绑定的是Title（因为Title是public，而title是private），所以如果要让前台做出变化，需要在赋值语句 title="news";后面再执行 RaisePropertyChanged(() => Title);

using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.CommandWpf;
using System.Text.RegularExpressions;
using System.Windows.Input;

namespace MVVM.ViewModel
{
    public class MainViewModel : ViewModelBase
    {
        private string title;

        public string Title
        {
            get { return title; }
            //set { Set(ref title, value); }
            set
            {
                if (title == value) { return; }
                title = value;
                RaisePropertyChanged(() => Title);
            }
        }

        public ICommand ChangeTitleCommand { get; set; }

        public MainViewModel()
        {
            Title = "Hello World";
            ChangeTitleCommand = new RelayCommand(ChangeTitle);
        }
        private void ChangeTitle()
        {
            string res="";
            string line = "root@HZ-CAS01-CVK01:~#";
            string pattern = ".*@(.*):.*";
            Regex re = new Regex(pattern);
            MatchCollection matches = re.Matches(line);
            foreach (Match m in matches)
            {
                GroupCollection groups = m.Groups;
                res = groups[1].Value;
            }
            //在这里直接对字段赋值，不进入set代码段，属性和字段同时被赋予新值news
            title = "news";
            RaisePropertyChanged(() => Title);

        }
    }
}

using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.CommandWpf;
using System.Text.RegularExpressions;
using System.Windows.Input;

namespace MVVM.ViewModel
{
    /// <summary>
    /// This class contains properties that the main View can data bind to.
    /// <para>
    /// Use the <strong>mvvminpc</strong> snippet to add bindable properties to this ViewModel.
    /// </para>
    /// <para>
    /// You can also use Blend to data bind with the tool's support.
    /// </para>
    /// <para>
    /// See http://www.galasoft.ch/mvvm
    /// </para>
    /// </summary>
    public class MainViewModel : ViewModelBase
    {
        private string title;

        public string Title
        {
            get { return title; }
            set
            {
                if (title == value) { return; }
                title = value;
                RaisePropertyChanged(() => Title);
            }
        }

        public ICommand ChangeTitleCommand { get; set; }
        /// <summary>
        /// Initializes a new instance of the MainViewModel class.
        /// </summary>
        public MainViewModel()
        {
            Title = "Hello World";
            ChangeTitleCommand = new RelayCommand(ChangeTitle);


            ////if (IsInDesignMode)
            ////{
            ////    // Code runs in Blend --> create design time data.
            ////}
            ////else
            ////{
            ////    // Code runs "for real"-
            ////}
        }
        private void ChangeTitle()
        {
            string res="";
            string line = "root@HZ-CAS01-CVK01:~#";
            string line1 = "<WX5504>";
            string line2 = "[fangkuohao]";
            //string pattern = "@(?:.*@(.*):~#)|(?:<(.*)>)|(?<=[)(.*)(?=>])|(?:(.*)>|#))";
            string pattern = ".*@(.*):.*";
            Regex re = new Regex(pattern);
            MatchCollection matches = re.Matches(line);
            foreach (Match m in matches)
            {
                GroupCollection groups = m.Groups;
                res = groups[1].Value;
            }
            Title = res;
        }
    }
}