On Unity's script execution sequence

First, the order of adding scripts

This is an official script sequence diagram

Generally, when we bind the script to the game object, or click the reset button of the bound script, Reset() will be called

When we initialize an object, we will first call Awake() and then call OnEnable()

GameObject.instantiate(o);

start() is called before the first call to update(), sometimes start() will be executed immediately after Awake(), OnEnable() is executed, in the same frame

The execution order of onDisable() and onDestroy() is a bit special:

The first situation:

　　 For different scripts on different objects, there is no order of execution, and they must be executed in pairs (onDestroy() must be called after onDisable() is called)

　　eg：

gameobject1:
    sc1.cs
    sc2.cs
gameobject2:
    sc3.cs
    sc4.cs
gameobject3:
    sc5.cs
    sc6.cs

gameobject1.sc1.onDisable()->gameobject1.sc1.onDestroy()->gameobject3.sc5.onDisable()->

gameobject3.sc5.onDestroy()

[If you follow the previous rules, the gameobject3 script should be executed first, but this is not the case]

The second situation:

On different scripts of the same object, these two methods follow the script

The index in m_component is executed in sequence, and it is not executed in pairs, the index is executed from small to large, the earliest join the earliest call onDisable() and onDestroy()

gemeobject2.sc3.onDisable()->gameobject2.sc4.onDisable()->

gameobject2.sc3.onDestroy->gameobject2.sc4.onDestroy()

Here these scripts first call onDisable() before calling onDestroy().

Second, how to customize the execution order of multiple scripts

Key points: in unity, you can click edit->project settings->Script->Execution Order to customize the script execution order,

When we do not set the script execution order, the script is executed according to the standard of Default Time (you can add objects in the hireachy unity and add scripts in the inspector

Treated as a stack, according to the first-in first-out principle, the first added script of the added object is executed first.

You can click the + sign to add objects to the execution list

1 is the execution order of the script. When the value of your execution order is smaller, it will be executed first. It is executed before the default time above the default time and below the default time

Executed after the default time

The above setting is achieved by modifying the excution order of the meta file (go to your own code directory) corresponding to each script.

Third, the nature of the script execution sequence

In our scene file .unity, the scene file is a YAML document

Each script corresponds to a fileid, the smaller the fileid, the more it will be executed first

4. Use

If your script A will use an object c in another script B, in order to prevent you from calling c before B initialization, a null pointer appears, you must let script B mount after A (so that B will first initialization),

Another important point is that you must write the initialization of object c in the Awake() method of script B, because start() is not called immediately after initialization, but when the current update frame, start( )

It will be called once before the first call to update(). In this case, if you write the initialization of object c in the start() method of script B, it is likely that the awake() of all scripts has run out, but the object c has not initialization,

In this way, a null pointer appears. Therefore, it is safe to initialize the object c in the awake() method of script B, and write the calling object c in the start() of script A

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