MVVM 绑定基类 BindableBase

MVVM 绑定基类 BindableBase

绑定基类用于VM(ViewModel)层中，具体代码如下

	public abstract class BindableBase : INotifyPropertyChanged
    {
        /// <summary>
        /// Occurs when a property value changes.
        /// </summary>
        public event PropertyChangedEventHandler PropertyChanged;

        /// <summary>
        /// Checks if a property already matches a desired value. Sets the property and
        /// notifies listeners only when necessary.
        /// </summary>
        /// <typeparam name="T">Type of the property.</typeparam>
        /// <param name="storage">Reference to a property with both getter and setter.</param>
        /// <param name="value">Desired value for the property.</param>
        /// <param name="propertyName">Name of the property used to notify listeners. This
        /// value is optional and can be provided automatically when invoked from compilers that
        /// support CallerMemberName.</param>
        /// <returns>True if the value was changed, false if the existing value matched the
        /// desired value.</returns>
        protected virtual bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)
        {
            if (Equals(storage, value)) return false;

            storage = value;
            RaisePropertyChanged(propertyName);

            return true;
        }

        /// <summary>
        /// Checks if a property already matches a desired value. Sets the property and
        /// notifies listeners only when necessary.
        /// </summary>
        /// <typeparam name="T">Type of the property.</typeparam>
        /// <param name="storage">Reference to a property with both getter and setter.</param>
        /// <param name="value">Desired value for the property.</param>
        /// <param name="propertyName">Name of the property used to notify listeners. This
        /// value is optional and can be provided automatically when invoked from compilers that
        /// support CallerMemberName.</param>
        /// <param name="onChanged">Action that is called after the property value has been changed.</param>
        /// <returns>True if the value was changed, false if the existing value matched the
        /// desired value.</returns>
        protected virtual bool SetProperty<T>(ref T storage, T value, Action onChanged, [CallerMemberName] string propertyName = null)
        {
            if (Equals(storage, value)) return false;

            storage = value;
            onChanged?.Invoke();
            RaisePropertyChanged(propertyName);

            return true;
        }

        /// <summary>
        /// Raises this object's PropertyChanged event.
        /// </summary>
        /// <param name="propertyName">Name of the property used to notify listeners. This
        /// value is optional and can be provided automatically when invoked from compilers
        /// that support <see cref="CallerMemberNameAttribute"/>.</param>
        protected void RaisePropertyChanged([CallerMemberName]string propertyName = null)
        {
            //TODO: when we remove the old OnPropertyChanged method we need to uncomment the below line
            //OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
            OnPropertyChanged(propertyName);
        }

        /// <summary>
        /// Notifies listeners that a property value has changed.
        /// </summary>
        /// <param name="propertyName">Name of the property used to notify listeners. This
        /// value is optional and can be provided automatically when invoked from compilers
        /// that support <see cref="CallerMemberNameAttribute"/>.</param>
        [Obsolete("Please use the new RaisePropertyChanged method. This method will be removed to comply wth .NET coding standards. If you are overriding this method, you should overide the OnPropertyChanged(PropertyChangedEventArgs args) signature instead.")]
        protected virtual void OnPropertyChanged([CallerMemberName]string propertyName = null)
        {
            OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
        }

        /// <summary>
        /// Raises this object's PropertyChanged event.
        /// </summary>
        /// <param name="args">The PropertyChangedEventArgs</param>
        protected virtual void OnPropertyChanged(PropertyChangedEventArgs args)
        {
            PropertyChanged?.Invoke(this, args);
        }

    }

没错，这是我抄的。

这段代码在VS2015中可以正常运行，低版本的VS可能无法正常编译通过，比如

1. [CallerMemberName]是.net 4.5中的定制特性，表示调用者名字。
2. ?.也是新语法，表示先判断.前面的对象是否为空，如果为空，那么.后面的方法不执行，如果不为空，那么执行

接下来，测试此类的能否正常运转

解决方案目录如上图所示

MainWindowViewModel.cs中代码：

    public class MainWindowViewModel : BindableBase
    {
        public MainWindowViewModel()
        {
            Content = "test";
        }

        private string _content;

        public string Content
        {
            get
            {
                return _content;
            }
            set
            {
                // 使用BindableBase中的SetProperty 不需要指定属性名 [CallerMemberName]已经帮我们做好了
                SetProperty(ref _content, value);
            }
        }
    }

MainWindow.xaml中代码：

<Window x:Class="MvvmBindableBase.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:MvvmBindableBase"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <!-- 接下来3行 为此Window指定数据上下文 -->
    <Window.DataContext>
        <local:MainWindowViewModel />
    </Window.DataContext>
    <Grid>
        <!-- 将TextBlock中Text依赖属性绑定到数据上下文中的Content属性 -->
        <TextBlock Text="{Binding Content}" VerticalAlignment="Center" HorizontalAlignment="Center"/>
    </Grid>
</Window>

运行结果：