Unity как найти объект по компоненту

Introduction — What we are going to do and why

In this arti­cle we are going to see a method that will allow us to find a COMPONENT of a spe­cif­ic type in Uni­ty from a Script, for exam­ple to find a com­po­nent type AudioSource, Col­lid­er or even a Script that we have cre­at­ed and assigned to a GameOb­ject. The pur­pose of that is to have the ref­er­ence of that com­po­nent inside our Script and to be able to use it accord­ing to our needs. For exam­ple if we want to call a func­tion that is defined in anoth­er Script we are going to need the ref­er­ence of the instance of that oth­er Script to be able to do it.

The method that we are going to see con­sists of using a code instruc­tion that checks each GameOb­ject of the hier­ar­chy and its com­po­nents until it finds the com­po­nent of the type that we indi­cate, if there is a com­po­nent of that type present in the scene the instruc­tion will return it as the exe­cu­tion result and we will be able to store that com­po­nent in a vari­able or to use it imme­di­ate­ly to exe­cute some sim­ple action on the com­po­nent that we found. If on the oth­er hand there is no com­po­nent of that type in any GameOb­ject of the scene, the instruc­tion will return Null and that could lead to an error of type Null­Ref­er­ence­Ex­cep­tion.

In the following video we see how to implement this method to find a component that is unique in the scene

After find­ing that scene com­po­nent we use it to ref­er­ence its GameOb­ject because that is the idea of the video series, but this part is not nec­es­sary, you can use the com­po­nent for what­ev­er you need.

When is this method useful?

• This method is effec­tive when the com­po­nent we are look­ing for is unique in the scene, if there is more than one com­po­nent of the same type there is no guar­an­tee of find­ing pre­cise­ly the one we are look­ing for.
• It is rec­om­mend­ed to use this method in some ini­tial­iza­tion func­tion like Awake or Start.
• It is not rec­om­mend­ed to use this method inside update func­tions like Update because they imply to tra­verse in the worst case the whole hier­ar­chy of the scene. Unless the pro­gram flow is some­how con­trolled so that the instruc­tion is exe­cut­ed only once.
• If the com­po­nent you want to find is going to be used more than once, it is advis­able to find it once and store it in a glob­al vari­able so that it can be used as many times as necessary.

Detailed procedure of finding a component from the scene through code

Initial conditions

We start from a Script called «Find­Ref­er­ence­O­fAnOb­ject» in which we are going to find the ref­er­ence of a cer­tain GameOb­ject that is in the scene in Uni­ty, inside the Script we will use that ref­er­ence to print its name in con­sole with the instruc­tion of the line 13 of the fig­ure 1.

The hier­ar­chy of the scene that we are going to use is com­posed by the GameOb­jects that are shown in fig­ure 2, the object «Script-GameOb­ject» is the one that has the Script in fig­ure 1 assigned and it is the one that will be in charge of find­ing the ref­er­ences, in fig­ure 3 you can see the inspec­tor of this GameOb­ject, where the Script is assigned.

The «GDT (Object to Find)» object seen in fig­ure 2 is the object we want to find from the script, so if we suc­ceed we should see the name of this object print­ed on the console.

Find the reference of a GameObject that has a specific component

If we know that the GameOb­ject we are inter­est­ed in find­ing has a spe­cif­ic com­po­nent assigned to it, such as a «Cam­era», «Rigid­body», «AudioSource» com­po­nent or a script we have cre­at­ed our­selves, we can use that knowl­edge to find the GameOb­ject reference.

I will cre­ate a script called «Some­Script» and assign it to the GameOb­ject we want to find, as shown in fig­ures 4 and 5.

Using the instruc­tion «FindObjectOfType<T>()», where T is the type of object we are look­ing for (in our case it is «Some­Script» type), we can find the ref­er­ence of the «Some­Script» instance that is assigned to that GameOb­ject, then using the dot oper­a­tor we can access the GameOb­ject to which that Script is assigned.

The instruc­tion that does all this can be seen in line 20 of fig­ure 6.

When this instruc­tion is exe­cut­ed, Uni­ty will check all the objects in the hier­ar­chy and each one of its com­po­nents until it finds a «Some­Script» type object, when it finds it it returns it as a result, but since we are inter­est­ed in the GameOb­ject to which that Script is assigned, we use the dot oper­a­tor and access the «gameOb­ject» field. If there is no object that has the «Some­Script» com­po­nent assigned to it we will have a null ref­er­ence error because we are using the «object­ToFind» field in line 22 of fig­ure 6.

To keep in mind, if we have more than one GameOb­ject that has assigned the com­po­nent we are look­ing for, Uni­ty will return the first com­po­nent that it finds in its reg­is­ter, in this case ambi­gu­i­ties could arise, we could obtain the ref­er­ence of a dif­fer­ent object to the one we want.