Error message in Angular Console: ERROR - Unable to access properties of an undefined value while attempting to read 'data'

The Console is showing an error:

ERROR TypeError: Cannot read properties of undefined (reading 'data")

at Oviewer Component 15A11Selected (oviewer.component.ts:97:37)

at OviewerComponent.checkbeaLabel (aviewer.component.ts:114:22)

at Oviewer Component th 26 Template (oviewer.component.html:79:68)


File: Oviewer.component.html


<div class="stable mat-elevation-z8">

<table mat-table [dataSource]="dataSource" class="mat-elevation-z8">

<!-- Checkbox Column --> 
<ng-container matColumnDef="select">

<th mat-header-cell *matHeaderCellDef>

<mat-checkbox

(change)="$event? toggleAllRows(): null" color="primary"

[checked]="selection.hasValue() && isAllSelected()"

[indeterminate]-"selection.hasValue() && lisAllSelected()"

[aria-label]="checkboxLabel()"

</mat-checkbox>

File: Oviewer.component.ts


iSAllSelected() {

const numSelected =this.selection.selected.length;

const numRows =this.dataSource.data.length;

return numSelected === numRows;

/** Selects all rows if they are not all selected; otherwise clear selection.*/

toggleAllRows() {

if (this.isAllSelected())

{

this.selection.clear();

return;

}

this.selection.select(...this.dataSource.data);

}

/** The label for the checkbox on the passed row */

checkboxLabel(row?: any): string { if (!row) { return ${this.isAllSelected() ? 'deselect' : 'select') all';

}

I am having trouble finding a solution for this issue. Can someone please assist me in understanding why I am encountering this Console error?

Answer №1

When encountering an error message, it is crucial to pay attention to the details. In this case, the error indicates that on line 97 of oviewer.component.ts, there is an attempt to access a property called 'data' of an object that has not been defined.

Although the exact line numbers were not provided, it seems likely that the issue lies in the following code snippet:

this.selection.select(...this.dataSource.data);

The 'dataSource' object acts as a wrapper for your data. To make use of it effectively, you need to ensure that it is properly initialized. This can be done either within the class itself or in the constructor using something like dataSource = new DataSource([]). Once initialized, the 'DataSource' will be ready for manipulation.

Answer №2

Before accessing the "data", it is important to implement a validation process. See below for an example:

const rowCount = this.dataCollection && this.dataCollection.info ? this.dataCollection.info.length : [];

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