# Trigger listeners when modifying element Observable{Matrix}

**URL:** <https://discourse.julialang.org/t/trigger-listeners-when-modifying-element-observable-matrix/67937>\
**Category:** General Usage\
**Tags:** makie\
**Created:** [September 9, 2021, 1:51pm UTC](https://discourse.julialang.org/t/trigger-listeners-when-modifying-element-observable-matrix/67937 "2021-09-09T13:51:26Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![theogf](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/theogf/32/1987_2.png) [@theogf](https://discourse.julialang.org/u/theogf)\
**Post date:** [September 9, 2021, 1:51pm UTC](https://discourse.julialang.org/t/trigger-listeners-when-modifying-element-observable-matrix/67937/1 "2021-09-09T13:51:26Z")

</div>

If I create an `Observable{Matrix}` :

```julia
X = Observable(rand(3, 3))

```

and that I have some listeners on `X`

```julia
a = @lift sum($X)
5.7....

```

Is there any way for this listener to be triggered when I only modify values of `X`:

```julia
X[][1, 2] = 3.0
a[]
5.7...

```

The only solution I found was to put an additional trigger:

```julia
trigger = Observable(true)
a = @lift sum($X) * $trigger
X[][1, 2] = 3.0
trigger[] = true
a[]
8.11....

```

---

<div class="post-metadata">

**Author:** ![jules](https://avatars.discourse-cdn.com/v4/letter/j/41988e/32.png) [@jules](https://discourse.julialang.org/u/jules)\
**Post date:** [September 9, 2021, 2:07pm UTC](https://discourse.julialang.org/t/trigger-listeners-when-modifying-element-observable-matrix/67937/2 "2021-09-09T14:07:08Z")

</div>

Before you’d often see

```julia
array_observable[][1] = rand()
array_observable[] = array_observable[]

```

but I prefer the more explicit

```julia
array_observable[][1] = rand()
notify(array_observable)

```

---

<div class="post-metadata">

**Author:** ![theogf](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/theogf/32/1987_2.png) [@theogf](https://discourse.julialang.org/u/theogf)\
**Post date:** [September 9, 2021, 2:15pm UTC](https://discourse.julialang.org/t/trigger-listeners-when-modifying-element-observable-matrix/67937/3 "2021-09-09T14:15:04Z")

</div>

Thanks! I was not aware of `notify`!