Angular Data Grid: Cell Renderer

The job of the grid is to lay out the cells. By default the grid will create the cell values using simple text. If you want more complex HTML inside the cells you can achieve this using cell renderers.

Simple Cell Renderer

Below is a simple example of cell renderer class:

import {Component} from "@angular/core";

import {ICellRendererParams} from "@ag-grid-community/core";

@Component({
   selector: 'total-value-component',
   template: `
         <span>
             <span>{{cellValue}}</span>&nbsp;
             <button (click)="buttonClicked()">Push For Total</button>
         </span>
   `
})
export class TotalValueRenderer {
   private cellValue: string;

   // gets called once before the renderer is used
   agInit(params: ICellRendererParams): void {
       this.cellValue = this.getValueToDisplay(params);
   }

   // gets called whenever the cell refreshes
   refresh(params: ICellRendererParams) {
       // set value into cell again
       this.cellValue = this.getValueToDisplay(params);
   }

   buttonClicked() {
       alert(`${this.cellValue} medals won!`)
   }

   getValueToDisplay(params: ICellRendererParams) {
       return params.valueFormatted ? params.valueFormatted : params.value;
   }
}

Simple Cell Renderer Example

The example below shows a simple cell renderer in action. It uses a cell renderer to render a hash (#) symbol for each medal won (instead of the medal count), and the MedalCellRenderer defined in the code snippet above for the Total column:

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Cell Renderer Component

The interface for the cell renderer component is as follows:

interface AgRendererComponent {
   // Optional - Params for rendering
   agInit(params: ICellRendererParams): void;

   // Optional - Return true if you want to manage a cell refresh yourself, otherwise return false.
   // If you return false, the grid will remove the component from the DOM and create  a new component in its place 
   // with the new values.
   refresh(params: ICellRendererParams): boolean;
}

The interface for the cell renderer parameters is as follows:

getValue = () => any;

setValue = (value: any) => void;

formatValue = (value: any) => any;

refreshCell = () => void;

registerRowDragger = (
    rowDraggerElement: HTMLElement,
    dragStartPixels?: number,
    value?: string,
    suppressVisibilityChange?: boolean
) => void;

Registering Cell Renderers with Columns

See the section registering custom components for details on registering and using custom cell renderers.

Component Refresh

Component refresh needs a bit more explanation. Here we go through some of the finer details.

Events Causing Refresh

The grid can refresh the data in the browser, but not every refresh / redraw of the grid results in the refresh method of your cell renderer getting called. The following items are those that do cause refresh to be called:

• Calling rowNode.setDataValue(colKey, value) to set a value directly onto the rowNode. This is the preferred API way to change one value from outside of the grid.
• When editing a cell and editing is stopped, so that cell displays new value after editing.
• Calling api.refreshCells() to inform grid data has changed (see Refresh).

If any of the above occur and the grid confirms the data has changed via Change Detection, then the refresh() method will be called.

The following will not result in the cell renderer's refresh method being called:

• Calling rowNode.setData(data) to set new data into a rowNode. When you set the data for the whole row, the whole row in the DOM is recreated again from scratch.
• Scrolling the grid vertically causes columns (and their containing cells) to be removed and inserted due to column virtualisation.

All of the above will result in the component being destroyed and recreated.

Grid vs Component Refresh

The refresh method returns back a boolean value. If you do not want to handle the refresh in the cell renderer, just return back false from an otherwise empty method. This will indicate to the grid that you did not refresh and the grid will instead destroy the component and create another instance of your component from scratch instead.

Change Detection

As mentioned in the section on Change Detection, the refresh of the cell will not take place if the value getting rendered has not changed.

Cell Renderer Component Lifecycle

The lifecycle of the cell renderer is as follows:

• The component will be instantiated.
• agInit() is called once (with the corresponding cell's parameters supplied).
• The component's GUI will be inserted into the grid 0 or 1 times (the component could get destroyed first, i.e. when scrolling quickly).
• refresh() is called 0...n times (i.e. it may never be called, or called multiple times).
• The component is destroyed once.

In other words, component instantiation, agInit and destruction are always called exactly once. The component's GUI will typically get rendered once unless the component is destroyed first. refresh() is optionally called multiple times.

Cell Rendering Flow

The diagram below (which is taken from the section Value Getters & Formatters) summarises the steps the grid takes while working out what to render and how to render.

In short, a value is prepared. The value comes using either the colDef.field or the colDef.valueGetter. The value is also optionally passed through a colDef.valueFormatter if it exists. Then the value is finally placed into the DOM, either directly, or by using the chosen colDef.cellRenderer.

Complementing Cell Renderer Params

On top of the parameters provided by the grid, you can also provide your own parameters. This is useful if you want to 'configure' your cell renderer. For example, you might have a cell renderer for formatting currency but you need to provide what currency for your cell renderer to use.

Provide params to a cell renderer using the colDef option cellRendererParams.

// define cellRenderer to be reused
@Component({
   selector: 'my-app',
   template: `<span [style.colour]="params.color">{{params.value}}</span>`
})
class ColourCellRenderer {
   params: ICellRendererParams;

   agInit(ICellRendererParams) {
       this.params = params;
   }
}

@Component({
   selector: 'my-app',
   template: `
       <ag-grid-angular
               class="ag-theme-alpine"
               [columnDefs]="columnDefs"
               [frameworkComponents]="frameworkComponents"
               ...other properties>        
       </ag-grid-angular>`
})
export class AppComponent {
   private columnDefs = [
       {
           headerName: "Colour 1",
           field: "value",
           cellRendererParams: {
              color: 'guinnessBlack'
           }
       },
       {
           headerName: "Colour 2",
           field: "value",
           cellRendererParams: {
              color: 'irishGreen'
           }
       }
   ];

  private frameworkComponents = {
      'colourCellRenderer': ColourCellRenderer
  };

  ..other methods
}

Data in Cell Renderers

Sometimes the data property in the parameters given to a cell renderer might not be populated. This can happen for example when using row grouping (where the row node has aggData and groupData instead of data), or when rows are being loaded in the Infinite Row Model and do not yet have data. It is best to check that data does exist before accessing it in your cell renderer, for example:

Here we use the safe navigation operator (?) to ensure that both params and data are valid before attempting to access theBoldValue:

// cell renderer component  
@Component({
   selector: 'my-app',
   template: `<span>{{params?.data?.theBoldValue}}</span>`
})
class CellRendererComponent {
   params: ICellRendererParams;

   agInit(ICellRendererParams) {
       this.params = params;
   }
}

Cell Renderer Function

Instead of using an Angular component, it's possible to use a simple function for a cell renderer.

This is probably most useful if you have a simple String value to render and want to avoid the overhead of an actual Angular component.

In the example below we're outputting a simple string value that depends on the cell value:

@Component({
   selector: 'my-app',
   template: `
       <ag-grid-angular
               class="ag-theme-alpine"
               [columnDefs]="columnDefs"
               ...other properties>
       </ag-grid-angular>`
})
export class AppComponent {
   private columnDefs = [
       {
           headerName: "Value",
           field: "value",
           cellRenderer: params => params.value > 1000 ? "LARGE VALUE" : "SMALL VALUE"
       }
    ];
    ..other methods
}

It is also possible to write a JavaScript-based cell renderer function - refer to the docs here for more information

Complex Cell Renderer Example

The example below shows five columns formatted, demonstrating each of the methods above.

• 'Month' column uses cellStyle to format each cell in the column with the same style.
• 'Max Temp' and 'Min Temp' columns uses the Function method to format each cell in the column with the same style.
• 'Days of Air Frost' column uses the Component method to format each cell in the column with the same style
• 'Days Sunshine' and 'Rainfall (10mm)' use simple functions to display icons.

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Accessing Cell Renderer Instances

After the grid has created an instance of a cell renderer for a cell it is possible to access that instance. This is useful if you want to call a method that you provide on the cell renderer that has nothing to do with the operation of the grid. Accessing cell renderers is done using the grid API getCellRendererInstances(params).

getCellRendererInstances = (
    params: GetCellRendererInstancesParams = {}
) => ICellRenderer[];

interface GetCellRendererInstancesParams {
  // Optional list of row nodes to restrict operation to 
  rowNodes?: RowNode[];
  // Optional list of columns to restrict operation to 
  columns?: (string | Column)[];
}

interface ICellRenderer {
  // Get the cell to refresh. Return true if successful. Return false if not (or you don't have refresh logic),
  // then the grid will refresh the cell for you. 
  refresh(params: ICellRendererParams): boolean;
}

An example of getting the cell renderer for exactly one cell is as follows:

// example - get cell renderer for first row and column 'gold'
const firstRowNode = gridOptions.api.getDisplayedRowAtIndex(0);
const params = { columns: ['gold'], rowNodes: [firstRowNode] };
const instances = gridOptions.api.getCellRendererInstances(params);

if (instances.length > 0) {
    // got it, user must be scrolled so that it exists
    const instance = instances[0];
}

Not that this method will only return instances of the cell renderer that exists. Due to row and column virtualisation, renderers will only exists for the user can actually see due to horizontal and vertical scrolling.

The example below demonstrates custom methods on cell renderers called by the application. The following can be noted:

• The medal columns are all using the user defined MedalCellRenderer. The cell renderer has an arbitrary method medalUserFunction() which prints some data to the console.
• The Gold method executes a method on all instances of the cell renderer in the gold column.
• The First Row Gold method executes a method on the gold cell of the first row only. Note that the getCellRendererInstances() method will return nothing if the grid is scrolled past the first row.
• The All Cells method executes a method on all instances of all cell renderers.

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If your are using a framework component (detailed below), then the returned object is a wrapper and you can get the underlying cell renderer using getFrameworkComponentInstance()

// example - get cell renderer for first row and column 'gold'
const firstRowNode = gridOptions.api.getDisplayedRowAtIndex(0);
const params = { columns: ['gold'], rowNodes: [firstRowNode] };
const instances = gridOptions.api.getCellRendererInstances(params);

if (instances.length > 0) {
    // got it, user must be scrolled so that it exists
    const wrapperInstance = instances[0];
    const frameworkInstance = wrapperInstance.getFrameworkComponentInstance();
}

Example: Rendering using more complex Components

This example illustrates a few different ideas:

• Custom Cell Renderers
• Parent/Child Communication using context
• Storing the Grid API via the "Grid Ready" event, and using it later

   Example: Simple Dynamic Component

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Example: Rendering using nested Modules

Using more complex Angular Components in the Cell Renderers - specifically how you can use nested NgModule's within the grid.

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