iOS UITextField和NSTimer奇数

Question

In each view I instantiate a "KeyHandler" object that enables the app to handle physical keyboard input.

When the object is instantiated it creates a hidden textField that acts as first responder.

During instantiation the following code is called:

[NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(pollTextField:) userInfo:nil repeats: YES];

Poll text field looks like:

-(void) pollTextField:(NSTimer*) timer{
  NSString * str = self.textField.text;
  NSString * lastChar;
  if (!str || [str isEqualToString:@""]) {
    //no new text
  }else{

    lastChar = [str substringFromIndex:[str length] - 1];
    [self determineAction:lastChar];
    lastChar = @"";
    str = nil;
  }
  self.textField.text = @"";
}

When I press u on the physical keyboard, self.textField.text == u . However, the textField does not become blank -- even though I set it to @"". The second time pollTextField is called self.textField.text == uu, the third time it is == u and it cycles between u and uu even though I'm not pressing any keys. Another oddity is that the first time pollTextField is called self always includes all the correct instance variables, the next time it's called they are missing, even though self is still a KeyHandler instance and still has the same memory address.

EDIT: Here's how I'm creating the textField and keyhandler:

UITextField* textField = [[UITextField alloc] init];
[self.view addSubview:textField];

keyHandler = [[KeyHandler alloc] initWithTextField:textField];
keyHandler.delegate = self;
[textField release];

Answer 1

This looks like a memory issue.

How are you creating the textField in your code? Are you properly allocating it?

Did you trying step-debugging and checking if the textField is a valid object in the pollTextField function?

just set a breakpoint and type in the gdb console po textField to see what it gives you

Edit: *Well there you go, your answer is there. The Textfield is created, assigned to the view and then released, so it's life cycle ends when you release it.

The view is now owning it, but you can't reference it directly.

Add a tag value to the textfield then cast it from the tagvalue:

 UITextField* textField = [[UITextField alloc] init];
textField.tag = 200;
[self.view addSubview:textField];

keyHandler = [[KeyHandler alloc] initWithTextField:textField];
keyHandler.delegate = self;
[textField release];

Then in your pollTextField function do this:

UITextField* textField = (UITextField*)[self.view viewWithTag:200];

So it looks like:

-(void) pollTextField:(NSTimer*) timer{
    UITextField* textField = (UITextField*)[self.view viewWithTag:200];
    NSString * str = textField.text;
    NSString * lastChar;
    if (!str || [str isEqualToString:@""]) {
        //no new text
    }else{

        lastChar = [str substringFromIndex:[str length] - 1];
        [self determineAction:lastChar];
        lastChar = @"";
        str = nil;
    }
    textField.text = @"";
}