Infinite scrolling allows the grid to lazy load rows from the server depending on what the scroll position is of the grid. In its simplest form, the more the user scrolls down, the more rows get loaded.
The grid will have an 'auto extending' vertical scroll. That means as the scroll reaches the bottom position, the grid will extend the height to allow scrolling even further down, almost making it impossible for the user to reach the bottom. This will stop happening once the grid has extended the scroll to reach the last record in the table.
The grid will ask your application, via a datasource, for the rows in blocks. Each block contains a subset of rows of the entire data set. The following diagram is a high level overview.
When the grid scrolls to a position where there is no corresponding block of rows loaded, the model uses the provided datasource to get the rows for the requested block. In the diagram, the datasource is getting the rows from a database in a remote server.
To turn on infinite scrolling, you must a) set the grid property rowModelType to infinite and b) provide a datasource.
A datasource must be provided to do infinite scrolling. You specify the datasource as a grid property or using the grid API.
Changing the datasource after the grid is initialised will reset the infinite scrolling in the grid. This is useful if the context of your data changes, ie if you want to look at a different set of data.
In a nutshell, every time the grid wants more rows, it will call getRows() on the datasource. The datasource responds with the rows requested. Your datasource for infinite scrolling should implement the following interface:
The getRows() method takes the following parameters:
The getRows() function is called by the grid to load a block of rows into the browser side cache of blocks. It takes the following as parameters:
The success callback parameter lastRow is used to move the grid out of infinite scrolling. If the last row is known, then this should be the index of the last row. If the last row is unknown, then leave blank (undefined, null or -1). This attribute is only used when in infinite scrolling. Once the total record count is known, the lastRow parameter will be ignored.
Under normal operation, you will return null or undefined for lastRow for every time getRows() is called with the exception of when you get to the last block. For example, if block size is 100 and you have 250 rows, when getRows() is called for the third time, you will return back 50 rows in the result and set rowCount to 250. This will then get the grid to set the scrollbar to fit exactly 250 rows and will not ask for any more blocks.
The grid keeps the blocks in a cache. You have the choice to never expire the blocks, or to set a limit to the number of blocks kept. If you set a limit, then as you scroll down, previous blocks will be discarded and will be loaded again if the user scrolls back up. The maximum blocks to keep in the cache is set using the maxBlocksInCache property.
The block size is set using the grid property cacheBlockSize. This is how many rows each block in the cache should contain. Each call to your datasource will be for one block.
Aggregation and grouping are not available in infinite scrolling. This is because to do such would require the grid knowing the entire data set, which is not possible when using the infinite row model. If you need aggregation and / or grouping for large datasets, check the Enterprise Row Model for doing aggregations on the server side.
The grid cannot do sorting or filtering for you, as it does not have all of the data. Sorting or filtering must be done on the server side. For this reason, if the sort or filter changes, the grid will use the datasource to get the data again and provide the sort and filter state to you.
The example below makes use of infinite scrolling and caching. Notice that the grid will load more data when you bring the scroll all the way to the bottom.
Selection works on the rows in infinite scrolling by using the ID of the row node. If you do not provide ID's for the row nodes, the index of the row node will be used. Using the index of the row breaks down when (server side) filtering or sorting, as these change the index of the rows. For this reason, if you do not provide your own id's, then selection is cleared if sort or filter is changed.
To provide your own id's, implement the method getRowNodeId(data), which takes the data and should return the id for the data.
Once you have getRowNodeId() implemented, selection will persist across sorts and filters.
The following example extends the example above by adding server side sorting, filtering and persistent selection.
Any column can be sorted by clicking the header. When this happens, the datasource is called again with the new sort options.
The columns Age, Country and Year can be filtered. When this happens, the datasource is called again with the new filtering options.
When a row is selected, the selection will remain inside the grid, even if the grid gets sorted or filtered. Notice that when the grid loads a selected row (eg select first row, scroll down so the first block is removed form cache, then scroll back up again) the row is not highlighted until the row is loaded from the server. This is because the grid is waiting to see what the id is of the row to be loaded.
(note: the example below uses ag-Grid-Enterprise, this is to demonstrate the set filter with server side filtering, ag-Grid-Enterprise is not required for infinite scrolling)
The examples on this page use a loading spinner to show if the row is waiting for its data to be loaded. The grid does not provide this, rather it is a simple rendering technique used in the examples. If the data is loading, then the rowNode will have no id. So if you use the id as the value, the cell will get refreshed when the id is set.
Refer to section Cell Rendering for how to build cell renderers.
Infinite scrolling has a cache working behind the scenes. The following properties and API are provided to allow you control of the cache.
When infinite scrolling is active, this says how many rows beyond the current last row the scrolls should allow to scroll. For example, if 200 rows already loaded from server, and overflowSize is 50, the scroll will allow scrolling to row 250. Default is 1.
How many requests to hit the server with concurrently. If the max is reached, requests are queued. Default is 1, thus by default, only one request will be active at any given time.
How many blocks to cache in the client. Default is no limit, so every requested block is kept. Use this if you have memory concerns, so blocks least recently viewed are purged. If used, make sure you have enough blocks in the cache to display one whole view of the table (ie what's within the scrollable area), otherwise it won't work and an infinite loop of requesting blocks will happen.
How many rows to initially allow the user to scroll to. This is handy if you expect large data sizes and you want the scrollbar to cover many blocks before it has to start readjusting for the loading of additional data.
How many rows for each block in the cache.
Marks all the currently loaded blocks in the cache for reload. If you have 10 blocks in the cache, all 10 will be marked for reload. The old data will continue to be displayed until the new data is loaded.
Purges the cache. The grid is then told to refresh. Only the blocks required to display the current data on screen are fetched (typically no more than two). The grid will display nothing while the new blocks are loaded. Use this to immediately remove the old data from the user.
The row count defines how many rows the grid allows scrolling to.
The property maxRowFound is a boolean, true or false. When false, then the grid will allow scrolling beyond the rowCount looking for more rows. When the last row is found, maxRowFound becomes true, and the grid will only scroll to the last available row as it has finished looking for more data.
|setInfiniteRowCount(rowCount, maxRowFound)||Sets the rowCount and maxRowFound properties. The second parameter, maxRowFound, is optional and if left out, only rowCount is set. Set rowCount to adjust the height of the vertical scroll. Set maxRowFound to enable / disable searching for more rows. Use this method if you add or remove rows into the dataset and need to reset the number of rows or put the data back into 'look for data' mode.|
|getCacheBlockState()||Returns an object representing the state of the cache. This is useful for debugging and understanding how the cache is working.|
Inserts items at the provided location inside the grid. If you use this, you MUST ensure that the data store you are sourcing from (eg the database) is also updated, as the subsequent cache block loads will need to be consistent with what is inside the grid. Doing an insert will require rows to be moved after the insert location (pushed down to make room) - this can leave blank rows in blocks in the cache (if a block has to be moved down, and the previous block is not loaded for it to take rows from). If this is the case, then the block will be marked for a refresh.
Inserting rows into the infinite scrolling row model allows for your grid to be out of sync with the underlying data store and hence can either cause synchronisation issues, or simply difficult code to maintain even if you get it right, especially in multi-user environments. It is strongly suggested you don't use the insertItemsAtIndex() method, rather you update the source and then refresh the cache.
This method is not supported by infinite scrolling. It is not supported as the grid has no way of knowing the index of the rowNodes to be removed if the data is not currently loaded into the cache.
This method is not supported by infinite scrolling. It is not supported as the grid has no way of knowing the end of the data dataset to be appended to if the data is not currently loaded into the cache.
Adding / removing rows directly in the grid for infinite scrolling is not recommended as it will complicate your application. It will make your life easier if you update the data on the server and refresh the block cache.
Below demonstrates the different api methods via the buttons. The example outputs a lot of debugging items to the console because the grid property debug=true is set. The buttons are as follows:
As with all row models, it is possible to enable pagination with infinite scrolling. With infinite scrolling, it is possible to mix and match with the configuration to achieve different effects. The following examples are presented:
|Example||Page Size||Block Size||Comment|
|Example 1||Auto||Large||Most Recommended|
|Example 2||Equal||Equal||Recommended Sometimes|
Having smaller infinite blocks size than your pagination page size is not supported
You must have infinite block size greater than or equal to the pagination page size. If you have a smaller block size, the grid will not fetch enough rows to display one page. This breaks how infinite scrolling works and is not supported.
This example is the recommended approach. The infinite block size is larger than the pages size, so the grid loads data for a few pages, allowing the user to hit 'next' a few times before a server sided call is needed.
This example demonstrates having the page and block sizes equal. Here the server is hit every time a new page is navigated to.