koobas.hobune.stream
Coroutine, Start() and Update() execution order
Hi, I'm newbie in unity programming, here is one simple test program I wrote which I got a bit confusing on the execution orders:
public float startbegintime = 0;
public float startendtime =0 ;
public float updatestarttime = 0;
public int commonvar = 0;
public int updatecnt =0;
void Start() {
Debug.Log("Start begin");
startbegintime = Time.time;
StartCoroutine(myFunc());
startendtime = Time.time;
Debug.Log("Start end");
}
IEnumerator myFunc()
{
for(int i = 0; i<100; i++)
{
Debug.Log("myFunc Loop "+(i+1).ToString());
commonvar++;
yield return 0;
}
}
void Update () {
if(updatestarttime == 0)
{
updatestarttime= Time.time;
Debug.Log("Update started");
}
if(updatecnt<100)
{
commonvar++;
updatecnt++;
Debug.Log("Common var is "+commonvar.ToString());
}
}
Well, the console output is as follows:
Start begin
myFunc Loop 1
Start end
Update started
Common var is 2
Common var is 3
myFunc Loop 2
Common var is 5
myFunc Loop 3
Common var is 7
myFunc Loop 4
......
and the time variables values are startbegintime = startendtime = 0, updatestarttime =0.2
so by the output, I noticed that the execution order is like this:
Start begin -> first iteration of coroutine -> Start end -> first update -> second update -> second iteration of coroutine -> third update -> third iteration of coroutine ->......
So why is that there're 2 consecutive update call before the second iteration of coroutine?
I took a look at the documentation on execution order, seems I still can't make it clear. http://unity3d.com/support/documentation/Manual/Execution%20Order.html
which says:
Normal coroutine updates are run after the Update function returns.
Anybody has some ideas on this? Thanks!
Coroutines run every frame after update - but the primary rule here is that it is running once every frame.
On the first frame the coroutine runs because you tell it to - in Start, which is before Update - it will not run again on that frame. Then afterwards it runs in its normal position after Update.
If you want it to start after the first Update then either:
Start it in Update the first time
Ignore the first time it is called before update by the first line of it being yield return 0 - in this case Update will be called twice before the main body of the coroutine runs
No problem :) Can you mark the question as answered so it disappears from the unanswered list?
