Layers

A layer is a rectangular region of grid cells. A layer has methods to access its columns, rows, width and height. All layers implement the ILayer interface. A layer can be stacked on top of another layer in order to expose a transformed view of its underlying layer's grid cell structure. Layers are used in this way to encapsulate grid transformation behavior such as hiding and reordering columns.

Columns and rows in a layer are referenced either by position or index:

  • The position of a column/row in a layer corresponds to the physical location of the column/row in the current layer. Positions always start from 0 and increase sequentially.
  • The index of a column/row in a layer corresponds to the location of the column/row in the lowest level layer in the layer stack. Usually the lowest layer in the layer stack will be the DataLayer. Indexes are not necessarily ordered, and in some cases may not even be unique within a layer.

These concepts are illustrated by the following example:

		ColumnHideShowLayer C
		0 1 2 3 4 <- column positions
		1 0 3 4 5 <- column indexes
		

		ColumnReorderLayer B
		0 1 2 3 4 5 <- column positions
		2 1 0 3 4 5 <- column indexes
		

		DataLayer A
		0 1 2 3 4 5 <- column positions
		0 1 2 3 4 5 <- column indexes

In the above example, ColumnHideShowLayer C is stacked on top of ColumnReorderLayer B, which is in turn stacked on top of DataLayer A. The positions in DataLayer A are the same as its indexes, because it is the lowest level layer in the stack. ColumnReorderLayer B reorders column 0 of its underlying layer (DataLayer A) after column 2 of its underlying layer. ColumnHideShowLayer C hides the first column of its underlying layer (ColumnReorderLayer B).

Layers can also be laterally composed into larger layers. For instance, the GridLayer is composed of several layers/layer stacks for every region.

NatTable Architecture

Following you will find the existing layers in NatTable:

BlinkLayer
Enables the blink cell functionality i.e the cell blinks when the data in it is updated. This layer listens for the update events and caches them locally. During rendering it uses this cache to check if data in a cell has been updated.
ColumnGroupExpandCollapseLayer
...
ColumnGroupGroupHeaderLayer
...
ColumnGroupHeaderLayer
...
ColumnGroupReorderLayer
...
ColumnHeaderLayer
...
type: DimensionallyDependentLayer
ColumnHideShowLayer
Enables the hiding of columns. The layers underneath are not aware of hidden columns. When requests pass through this layer it manipulates them to return the columns positioned after the hidden columns.
ColumnReorderLayer
Tracks the reordered columns. Similar to the ColumnHideShowLayer, the other layers are unaware of column reordering.
CompositeFreezeLayer
...
type: CompositeLayer
CornerLayer
The CornerLayer is a layer that is used for the corner region of a grid. It is a DimensionallyDependentLayer which means its horizontal and vertical dimensions are dependent on the horizontal and vertical dimensions of other layers. Usually it will have a horizontal dependency to the row header layer (stack) and a vertical dependency to the column header layer (stack). As the CornerLayer is usually rendered as an empty cell, the base layer is a DataLayer which is created by using the DefaultCornerDataProvider.
DataLayer

The primary purpose of the DataLayer is to attach the IDataProvider to the table and supply data for the cells. It also handles resize commands and tracks column/row sizes via SizeConfig objects. This layer always works with column/row indexes i.e the position of the cell in the underlying data source. It is usually the lowermost layer in a layer stack.

The following specializations of the DataLayer exist:

  • DefaultColumnHeaderDataLayer
    Specialization of a DataLayer for the column header of a grid. Sets the size of the cells to width 100 and height 20 by default.
  • DefaultRowHeaderDataLayer
    Specialization of a DataLayer for the row header of a grid. Sets the size of the cells to height 40 and width 40 by default.
  • FilterRowDataLayer
    Needed for the filter row of a NatTable. Will handle filter commands, adds special filter row labels to filter row cells and provides constants that are needed to customize the filter row. It is not intended to use the FilterRowDataLayer itself.
  • GroupByDataLayer
    ...
  • SpanningDataLayer
    ...

FilterRowHeaderComposite
...
...
type: CompositeLayer uses FilterRowDataLayer
FreezeLayer
...
GlazedListsEventLayer
This layer is meant to be used if the backing data source is a GlazedLists instance. Its acts as a listener for the list insert/delete/update events and fires corresponding NatTable events. Hence, the table knows to repaint itself when the underlying data changes.
GridLayer

This is a top level layer used to divide up the table into grid regions. A layer or layer stack can then be assigned to each of these regions. This layer mostly serves to delegate functions to its lower layers.

There is a default implementation DefaultGridLayer that uses DefaultBodyLayerStack, ColumnHeaderLayer, RowHeaderLayer and CornerLayer which are created out of the data information given to one of the constructors.

GroupByHeaderLayer
...
type: DimensionallyDependentLayer
RowGroupHeaderLayer
...
RowHeaderLayer
...
type: DimensionallyDependentLayer
SelectionLayer

Enables selection of rows, columns or cells on the table. Adds keyboard / mouse configuration used to trigger selection and style configuration for special rendering of selection. Also hooks in the search and the tick update features. Uses the SelectionModel internally to track the selection state.

The SelectionLayer is part of the body region layer stack of a grid, but will be referenced by all other regions layer stacks. You can find further information on the SelectionLayer here.

SortHeaderLayer
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SummaryRowLayer
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ViewportLayer
Places a 'viewport' over the table. Introduces scroll bars over the table and keeps them in sync with the data being displayed. This is typically placed over the SelectionLayer.
ZoomLayer
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DefaultBodyLayerStack
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ColumnGroupBodyLayerStack
...