内容摘自：http://www.agrinei.com/gridviewhelper/gridviewhelper_en.htm

GridView在DataGrid上有很多改进，但仍然缺少一些非常重要的特性。GridView中不可使用的重复需求是创建组和汇总。要创建总结，我们可以轻松地编写RowDataBound事件。分组是一个更复杂的任务，需要更多的编码和调试。但当我们需要结合这两个特性时，事情就会变得一团糟。考虑到这一点，我已经实现了GridViewHelper，顾名思义，它是帮助创建组和总结的助手类。

使用GridViewHelper

下面我们将看到一些GridViewHelper示例。首先，我们展示将创建组和汇总的网格。样本数据来自Northwind数据库，有一些修改:

要为ItemTotal列创建一个摘要，我们只需要承诺的2行代码:

首先，我们创建GridViewHelper设置网格，在该网格中它将在构造函数中执行。然后，我们注册摘要，说明要执行的列名和摘要操作。下面的结果是:

在这个示例中，添加了一条新行来显示摘要。另一种方法是使用footer row来显示摘要，而不是创建一个新的。当在网格中添加一个新行时，只创建需要显示汇总列的所需单元格。使用footer，创建所有的单元格。在组摘要的情况下，所有单元的生成或仅需要的单元格是一个组属性。
现在我们将创建一个组。代码如下:

RegisterGroup方法的第一个参数定义了要创建的组的列。还可以创建一个复合组，包括列的数组。第二个参数指定该组是否为automatic。在这种情况下，将自动为组头创建一个新的行。第三个参数指定是否必须隐藏组列。ApplyGroupSort方法将网格的排序表达式设置为分组列，在本例中是ShipRegion。这需要对工作进行适当的分组，除非数据来自数据库。
在上面的样本中，ShipRegion的专栏已经被隐藏了:

Let's make something more interesting, let's add a summary to the created group. We need just one more line to register the summary to the group:

This time, the RegisterSummary method takes another parameter. The parameter specifies the name of the group to which the summary must be created. Group name is automatically generated from the group column names. If the group has only one column, group name will be the name of that column. If the group has more than one column, the group name will be the ordered concatenation of the columns that composes the group, joined with a plus sign ("+"): "ShipRegion+ShipName".

We can see below the grid with grouping and a summary for the group:

It's possible to create more than one group in the grid, simulating a hierarchical grouping, as seen below:

Result:

The grid after the cosmetics:

No value is displayed for the columns that don't have a summary operation defined. This makes sense because GridViewHelper doesn't know how to proceed to summarize the values found in the group rows to a unique value. This reminds the certain known message:

"Column 'column_name' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause."

It doesn't make sense to display the columns that don't have a summary operation, and to hide them we need to call a method:

I know, it's a big big name! The resulting grid can be seen below:

Summary operations

GridViewHelper has 3 built-in summary operations: sum, average and row count. A very useful feature is the possibility of define custom summary operations. To achieve this we need to provide two methods to the GridViewHelper. A method will be called for each row found in the grid (or group) and the other will be called to retrieve the result of the summary operation. Below we have a sample of a custom summary operation. The semi-dummy operation will return the minimum value found:

In the code above we can see the required methods signatures. Both receive the summarized group and column names. If the summary is not relative to a group, the group parameter will be null. The method that is called for each row found in the grid, receives also the value of the column in the current row.

The resulting grid can be seen below :

要为ItemTotal列创建一个摘要，我们只需要承诺的2行代码

First we create the GridViewHelper setting the grid in which it will act in the constructor. Then we register the summary specifying the column name and the summary operation to be performed. The result is below:

In this sample a new line was added to display the summary. Another option is to use the footer row to display the summary instead of creating a new one. When a new row is added to the grid, only the required cells to display the summarized columns are created. Using the footer, all the cells are created. In case of group summaries, generation of all cells or only the needed cells is a group attribute.

Now we will create a group. The code is shown below:

The first parameter of RegisterGroup method defines the columns to which the group must be created. It's also possible to create a composite group, consisting of an array of columns. The second parameter specifies if the group is automatic. In this case a new row will be created automatically for the group header. The third parameter specifies if the group columns must be hidden. The ApplyGroupSort method sets the sort expression of the grid as being the group columns, in this case, ShipRegion. This is required to grouping works properly, except if the data comes ordered from database.

In the above sample the column ShipRegion have been hidden:

Let's make something more interesting, let's add a summary to the created group. We need just one more line to register the summary to the group:

This time, the RegisterSummary method takes another parameter. The parameter specifies the name of the group to which the summary must be created. Group name is automatically generated from the group column names. If the group has only one column, group name will be the name of that column. If the group has more than one column, the group name will be the ordered concatenation of the columns that composes the group, joined with a plus sign ("+"): "ShipRegion+ShipName".

We can see below the grid with grouping and a summary for the group:

It's possible to create more than one group in the grid, simulating a hierarchical grouping, as seen below:

Result:

The grid after the cosmetics:

No value is displayed for the columns that don't have a summary operation defined. This makes sense because GridViewHelper doesn't know how to proceed to summarize the values found in the group rows to a unique value. This reminds the certain known message:

"Column 'column_name' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause."

It doesn't make sense to display the columns that don't have a summary operation, and to hide them we need to call a method:

I know, it's a big big name! The resulting grid can be seen below:

Summary operations

GridViewHelper has 3 built-in summary operations: sum, average and row count. A very useful feature is the possibility of define custom summary operations. To achieve this we need to provide two methods to the GridViewHelper. A method will be called for each row found in the grid (or group) and the other will be called to retrieve the result of the summary operation. Below we have a sample of a custom summary operation. The semi-dummy operation will return the minimum value found:

In the code above we can see the required methods signatures. Both receive the summarized group and column names. If the summary is not relative to a group, the group parameter will be null. The method that is called for each row found in the grid, receives also the value of the column in the current row.

The resulting grid can be seen below :

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