LINQ：动态Where子句，用于切换案例组合

Question

我有一个绑定到angridview的列表，我希望能够“动态”创建过滤器Where子句，同时由用户控制过滤器选项的组合。

按模型布尔属性过滤原始列表的最佳方法是什么，并允许切换过滤器的每个条件？

我知道filterdList不是nececery，但我已经看过的其他解决方案都不允许切换Where子句的条件。

public partial class Form1 : Form
{
    List<dummy> Origlist = new List<dummy> {
        new dummy { pk = 1 ,  istype1 = true,  istype2  = false, istype3=false, istype4=false },
        new dummy { pk = 2 ,  istype1 = true,  istype2 = false,  istype3=false, istype4=false },
        new dummy { pk = 3 ,  istype1 = false, istype2 = true,   istype3=false, istype4=false },
        new dummy { pk = 4 ,  istype1 = false, istype2 = true,   istype3=false, istype4=false },
        new dummy { pk = 5 ,  istype1 = false, istype2 = false,  istype3=true,  istype4=false },
        new dummy { pk = 6 ,  istype1 = false, istype2 = false,  istype3=true,  istype4=false },
        new dummy { pk = 7 ,  istype1 = false, istype2 = false,  istype3=false, istype4=true },
        new dummy { pk = 8 ,  istype1 = false, istype2 = false,  istype3=false, istype4=true },
        new dummy { pk = 9 ,  istype1 = false, istype2 = false,  istype3=true,  istype4=false },
        new dummy { pk = 10 , istype1 = false, istype2 = true,   istype3=false, istype4=false },
        new dummy { pk = 11 , istype1 = false, istype2 = false,  istype3=false, istype4=false }
        };
    List<dummy> filteredList = new List<dummy>(); 
    public Form1()
    {
        InitializeComponent();
    }

    private void Bind()
    {
        dataGridView1.DataSource = null;
        dataGridView1.DataSource = filteredList;
    }


    private void checkBox1_CheckedChanged(object sender, EventArgs e)
    {
        if (checkBox1.Checked)
        {
            filteredList.AddRange(Origlist.Where(a => a.istype1 == true).ToList());
        }
        else
        {
            filteredList.RemoveAll(a => a.istype1 == true);
        }
        Bind();
    }



    private void checkBox2_CheckedChanged(object sender, EventArgs e)
    {
        if (checkBox2.Checked)
        {
            filteredList.AddRange(Origlist.Where(a => a.istype2 == true).ToList());
        }
        else
        {
            filteredList.RemoveAll(a => a.istype2 == true);
        }
        Bind();
    }

    private void checkBox3_CheckedChanged(object sender, EventArgs e)
    {
        if (checkBox3.Checked)
        {
            filteredList.AddRange(Origlist.Where(a => a.istype3 == true).ToList());
        }
        else
        {
            filteredList.RemoveAll(a => a.istype3 == true);
        }
        Bind();
    }

    private void checkBox4_CheckedChanged(object sender, EventArgs e)
    {
        if (checkBox4.Checked)
        {
            filteredList.AddRange(Origlist.Where(a => a.istype4 == true).ToList());
        }
        else
        {
            filteredList.RemoveAll(a => a.istype4 == true);
        }
        Bind();
    }

}

Answer 1

尝试这样的事情（未经测试）：

public partial class Form1 : Form
{
    List<dummy> Origlist = new List<dummy> {
        new dummy { pk = 1 ,  istype1 = true,  istype2  = false, istype3=false, istype4=false },
        new dummy { pk = 2 ,  istype1 = true,  istype2 = false,  istype3=false, istype4=false },
        new dummy { pk = 3 ,  istype1 = false, istype2 = true,   istype3=false, istype4=false },
        new dummy { pk = 4 ,  istype1 = false, istype2 = true,   istype3=false, istype4=false },
        new dummy { pk = 5 ,  istype1 = false, istype2 = false,  istype3=true,  istype4=false },
        new dummy { pk = 6 ,  istype1 = false, istype2 = false,  istype3=true,  istype4=false },
        new dummy { pk = 7 ,  istype1 = false, istype2 = false,  istype3=false, istype4=true },
        new dummy { pk = 8 ,  istype1 = false, istype2 = false,  istype3=false, istype4=true },
        new dummy { pk = 9 ,  istype1 = false, istype2 = false,  istype3=true,  istype4=false },
        new dummy { pk = 10 , istype1 = false, istype2 = true,   istype3=false, istype4=false },
        new dummy { pk = 11 , istype1 = false, istype2 = false,  istype3=false, istype4=false }
    };

    Options options = new Options();

    private class Options {
        public bool istype1 { get; set; }
        public bool istype2 { get; set; }
        public bool istype3 { get; set; }
        public bool istype4 { get; set; }
    }

    public Form1()
    {
        InitializeComponent();
    }

    private void Bind()
    {
        dataGridView1.DataSource = null;
        dataGridView1.DataSource = OrigList.Where(a =>
          (options.istype1 && a.istype1) ||
          (options.istype2 && a.istype2) ||
          (options.istype3 && a.istype3) ||
          (options.istype4 && a.istype4)
        ).ToList();
    }


    private void checkBox1_CheckedChanged(object sender, EventArgs e)
    {
        options.istype1 = checkBox1.checked;
        Bind();
    }



    private void checkBox2_CheckedChanged(object sender, EventArgs e)
    {
        options.istype2 = checkBox2.checked;
        Bind();
    }

    private void checkBox3_CheckedChanged(object sender, EventArgs e)
    {
        options.istype3 = checkBox3.checked;
        Bind();
    }

    private void checkBox4_CheckedChanged(object sender, EventArgs e)
    {
        options.istype4 = checkBox4.checked;
        Bind();
    }

}

还有其他方法可以减少重复，但这是一个开始。

Answer 2

我想说最简单/最干净的方法是使用ADO.NET DataSet来处理你的数据，而不是使用一堆带有一些Linq查询的List。 ADO.NET DataSet是官方的Winforms生活方式 。

您可以将这些数据集/数据表与BindingSource组件一起用作DataGridView的DataSource，并使用BindingSource的Filter String属性。 这个String表达式可以通过一些If子句轻松构建，这些子句按照MSND DataColumn表达式语法测试CheckBox的状态和字符串连接。

还有一些其他干净的方法，比如使用IBindingListView接口的部分实现来扩展BindingList类。 但这是一些相当困难的东西，特别是当你知道微软已经为你为DataSet做了这项工作时...如果你不害怕，这篇文章是一个很好的起点。

Answer 3

可以为每个CheckBox重用单个事件处理程序，并且该事件处理程序可以将每个属性与相应的CheckBox进行比较。

List<dummy> Origlist = new List<dummy> 
{
    new dummy { pk = 1 ,  istype1 = true,  istype2 = false,  istype3=false, istype4=false },
    new dummy { pk = 2 ,  istype1 = true,  istype2 = false,  istype3=false, istype4=false },
    new dummy { pk = 3 ,  istype1 = false, istype2 = true,   istype3=false, istype4=false },
    new dummy { pk = 4 ,  istype1 = false, istype2 = true,   istype3=false, istype4=false },
    new dummy { pk = 5 ,  istype1 = false, istype2 = false,  istype3=true,  istype4=false },
    new dummy { pk = 6 ,  istype1 = false, istype2 = false,  istype3=true,  istype4=false },
    new dummy { pk = 7 ,  istype1 = false, istype2 = false,  istype3=false, istype4=true  },
    new dummy { pk = 8 ,  istype1 = false, istype2 = false,  istype3=false, istype4=true  },
    new dummy { pk = 9 ,  istype1 = false, istype2 = false,  istype3=true,  istype4=false },
    new dummy { pk = 10 , istype1 = false, istype2 = true,   istype3=false, istype4=false },
    new dummy { pk = 11 , istype1 = false, istype2 = false,  istype3=false, istype4=false }
};

public Form1()
{
    InitializeComponent();
}

private void checkBox_CheckedChanged(object sender, EventArgs e)
{
     dataGridView1.DataSource = Origlist.Where(a => 
         a.istype1 == checkBox1.Checked && 
         a.istype2 == checkBox2.Checked && 
         a.istype3 == checkBox3.Checked && 
         a.istype4 == checkBox4.Checked).ToList();
}