MVVM模式下的OpenFileDialog

对于MVVM模式下的ViewModel层来说，是不应该直接访问OpenFileDialog或者FolderBrowserDialog的，否则VM会变得难以测试。

参考StackOverFlow，对ViewModel进行改造，使OpenFileDialog动作也可以测试。

首先实现接口IIOService

    public interface IIOService
    {
        string OpenFileDialog(string srcFilter = "");

        IList<string> OpenFileDialogMultiselect(string srcFilter = "");

        string FolderBrowserDialog();
    }

在工程中实现该接口IOService

   public class IOService : IIOService
    {
        public string OpenFileDialog(string srcFilter = "")
        {
            var op = new System.Windows.Forms.OpenFileDialog();
            op.Filter = srcFilter;
            if (op.ShowDialog() == System.Windows.Forms.DialogResult.OK)            
                return op.FileName;
            
            return "";
        }

        public IList<string> OpenFileDialogMultiselect(string srcFilter = "")
        {
            var op = new System.Windows.Forms.OpenFileDialog();
            op.Filter = srcFilter;
            op.Multiselect = true;
            if (op.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                return op.FileNames;
            return new List<string>();
        }

        public string FolderBrowserDialog()
        {
            var path = new System.Windows.Forms.FolderBrowserDialog();
            var result = path.ShowDialog();
            if (result == System.Windows.Forms.DialogResult.OK)            
                return path.SelectedPath;
            
            return string.Empty;
        }
    }

这样就可以在测试的时候给VM注入一个实现该接口的桩对象，进而进行测试啦。