Angular 2: A guide to connecting Input with model property using getter and setter functions

I'm currently developing an Angular 2 web application. The model I have created consists of a few primary properties, along with other properties that are calculated based on those primary values.

For each property in my model, I have implemented getter methods. To ensure that the calculated properties stay up-to-date with the primary properties, I update the primary properties using setter methods that also recompute the calculated values. Here is a simplified snippet of my approach:

export class Model{
    private _keyValue: number;
    private _computedValue: number;

    getKeyValue(): number{
        return this._keyValue;
    }

    setKeyValue(value: number){
        this._keyValue = value;
        this.evaluateComputedValues(); // This process may take time
    }

    getComputedValue(): number{
        return this._computedValue;
    }
}

This methodology ensures the consistency of my model: whenever a primary property is modified, all related calculated properties are updated accordingly.

Now, my goal is to establish bindings between these properties and the component views. I have successfully displayed the computed property values using interpolation like so:

<div>{{model.getComputedValue()}}</div>

Nevertheless, I am uncertain about the optimal approach for binding the primary properties to input fields. The typical examples of two-way binding in Angular 2 utilize ngModel as shown below:

<input [(ngModel)]='model.property'>

However, this method appears to be tailored for simple properties. What I need is two-way binding that leverages my distinct getter and setter methods (getKeyValue and setKeyValue).

Is there a native solution available in Angular 2 to achieve this?

Answer №1

Make sure to implement this longer version

<input [ngModel]='model.getData()' (ngModelChange)="model.updateData($event)">

It's important to note that the retrieveData() methods will be executed every time there is a change detection process, which could happen frequently. Confirm that the accessors return the same value (especially for objects the same instance) and ensure they do not cause any side effects, or else you may encounter "Expression has changed since it was last checked ..." issues.

Answer №2

The Angular version being used here may vary, but in my version (v4.3.5) it is possible to bind directly to getter/setter methods of a field using ngModel. Here is an example of how to do so in the typescript file:

  get FormattedRevenue():string{
    return this.Revenue !== undefined ? `$${this.Revenue.toLocaleString()}` : '$0';
  }

  // Remove currency information and assign to Revenue
  set FormattedRevenue(value: string) {
    const revenueValue = value.replace(/[^\d]/g, '');
    this.Revenue = parseInt(revenueValue);
  }

And in the template file:

<input type="text" class="text-input" [(ngModel)]="businessData.FormattedRevenue" />

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