问题
I am having a problem of how to call a method once when the condition achieves many times! for example:
public void onLocaitonChanged(Location location){
// this if statement may achieve the condition many times
if(somethingHappened){
callAMethodOnce();// this method is called once even if the condition achieved again
}
}
Please help with that
回答1:
public void onLocaitonChanged(Location location){
// this if statement may achieve the condition many times
if(somethingHappened){
if (!isAlreadyCalled){
callAMethodOnce();// this method is called once even if the condition achieved again
isAlreadyCalled = true;
}
}
}
回答2:
boolean isHappendBefore = false;
public void onLocaitonChanged(Location location){
// this if statement may achieve the condition many times
if(somethingHappened && (! isHappendBefore) ){
isHappendBefore = true;
callAMethodOnce();// this method is called once even if the condition achieved again
}
}
回答3:
You could simply set a flag. If you just need it to only happen once with each instance of the Activity then set a member variable.
public class MyActivity extends Activity
{
boolean itHappened = false;
...
public void onLocaitonChanged(Location location)
{
// this if statement may achieve the condition many times
if(somethingHappened && !itHappened)
{
callAMethodOnce();// this method is called once even if the condition achieved again
itHappened = true;
}
}
If you want it to only happen once ever in the life of the application then set that variable as a SharedPreference
回答4:
set a class wide boolean
if(!hasRun){
callAMethodOnce();
hasRun = true;
}
回答5:
Maybe I don't understand your question correctly but from your problem definition I would suggest using a boolean variable something like.
boolean run = false;
public void onLocaitonChanged(Location location){
// this if statement may achieve the condition many times
if(somethingHappened && run == false){
run = true;
callAMethodOnce();// this method is called once even if the condition achieved again
}
}
Once the code under if statement gets executed once run would be true and there won't be any subsequent calls to callAMethodOnce()
来源：https://stackoverflow.com/questions/20150558/calling-a-method-once