Problem with stringByEvaluatingJavaScriptFromString

Question

I wanna to know abt "stringByEvaluatingJavaScriptFromString".

According to the apple doc. "The result of running script or nil if it fails."

I have a method in which inside a for loop i'm passing a string value to stringByEvaluatingJavaScriptFromString. what will it do ?? will this get response for every string or something else will happen?? I was doing like this...

- (void)loadWithStartPoint:(NSString *)startPoint endPoint:(NSMutableArray *)endPoints options:(UICGDirectionsOptions *)options {
    for (int idx = 0; idx < [endPoints count]; idx ++) 
    {
        NSString *msg = [NSString stringWithFormat:@"loadDirections('%@', '%@', %@)", startPoint, [endPoints objectAtIndex:idx], [options JSONRepresentation]];
        [googleMapsAPI stringByEvaluatingJavaScriptFromString:msg];
    }
}

Inorder to get response to every string what should I do? I think that it should get response to every string that i'm passing here. Please tell me what m doing wrong and how would i manipulate my code to get response to all strings that m passing. Any help would be appreciated .Thnx in advance.

Community · Accepted Answer · 2017-05-23 10:27:08Z

2

You should make your javascript method to return a default string or something if even an error occurs in the script.

function loadDirections()
{

try
  {
  //Your code goes here which returns some result
  }
catch(err)
  {
  var errorFlag = "ERROR";
return errorFlag;
  }
}

and then you should alter your Objective C code like below

NSString *msg = [NSString stringWithFormat:@"loadDirections('%@', '%@', %@)", startPoint, [endPoints objectAtIndex:idx], [options JSONRepresentation]];

if([msg isEqualToString:@"ERROR")
{

//Do some error handling

}
else
{

//Your actual code goes here

}

Update for the comment:

To solve your javascript asynchronous problem either (1) you can change your design and call the javascript method only after getting response from the first call (2) or else you can use NSTimer which will will give a little time for the execution. In my opinion changing your design as per the first option would be perfect.

Have a look at these questions stringByEvaluatingJavaScriptFromString doesn't always seem to work return value javascript UIWebView

edited May 23, 2017 at 10:27

CommunityBot

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answered Sep 26, 2011 at 6:20

sElanthiraiyan

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4 Comments

iCoder4777 Over a year ago

I'm handling that error thing properly.I only want to know how can i make stringByEvaluatingJavaScriptFromString to response each and every string that m passing. It is responding only to the last string that is being passed.

sElanthiraiyan Over a year ago

K now I got ur problem. Its happening because javascript is Asynchronous and ur obj c for loop is not waiting for the javascript function to execute fully. You can solve this by altering your design a little. Updated my answer.

iCoder4777 Over a year ago

ok...Can u describe a bit more, how can I be able to get my soln. How can i alter my code for the desired soln.

iCoder4777 Over a year ago

I have seen those links, but neither is suggesting how to pass more than one string to stringByEvaluatingJavaScriptFromString. can U be more clear? Thnx for the help.

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