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How do I use a compareWith Function with Angular Material?

In this screencast I talk about using a compareWith function with Angular Material.

Find the original vid on YouTube and check out the source on GitHub

Why won't my mat-select select items?

I'm working on an Angular project that includes a large legacy code base, and just spent a few hours trying to get a mat-select to actually select an item. No matter what I did it seemed like the selected item was always null. In case you're running into something similar, I'm going to show you how I fixed it.

First, I set up an Angular project and installed ng material.

Then, in a component, create a data provider:

dataSource = [
{label: 'one'},
{label: 'two'},
{label: 'three'},
{label: 'four'},
{label: 'five'},
{label: 'six'},
{label: 'seven'},
{label: 'eight'},
{label: 'nine'},
{label: 'ten'}

I just created a bunch of generic objects with a label property for the purposes of this sample. Also create a field to hold the selected value:


Now, create your mat-select. Start with the mat-form-field:

<!-- more stuff here -->

Inside that mat-form-field place the

<mat-select placeholder="Select a Number" [(ngModel)]="selectedItem" >
<!-- more stuff here -->

This is simple, it uses the ngModel to bind the selected item in the mat-select to the selectedItem property in the component class.

Now add the options:

<mat-option *ngFor="let item of dataSource" >

This uses mat-option and loops over the data source to create the items. Run the code and you should see something like this:

Select an item and you'll see the placeholder stays the same:

Whenever I tired to access the selectedItem in code it was always null or blank. What was going on? Did you see my omission yet?

When creating the mat-options, they need a value:

<mat-option *ngFor="let item of dataSource" [value]="item" >

Without these the mat-select has no idea how to match the selected item to an item in the data provider and the ngModel value will never get set. Once I put in the value everything started working again.

Play with the code here.

How do I switch between different NG Material Button Types?

ng-materal provides a bunch of button variants. Each button type is an HTML button that offers identical functionality, but with slightly different designs and colors. Here is an example of two buttons:

<button mat-flat-button>My Button 1</button>
<button mat-stroked-button>My Button 2</button>

If you drill into the button class, you'll see that all the button variants are implemented in the same code base, as directives.

I was doing a code review on a current project and saw that the code was conditionally determining which button type to display:

<button mat-flat-button *ngIf="condition">My Button 1</button>
<button mat-stroked-button *ngIf="!condition">My Button 1</button>

I was bugged by the fact that we were implementing two button components in our code for what was essentially a style change. That's when I started digging into the specific implementation and discovered that the primary difference between a mat-flat-button and a mat-stroked-button was style changes.

I proposed this alternate approach:

<button mat-button [ngClass]="condition?'mat-flat-button':'mat-stroked-button'">My Button 1</button>

We use the ngClass directive to conditionally flip the style between the flat-button and the stroked-button. It solved our issue with less code.

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