resizing UIPickerView
===

I'm trying to create an UIPickerView in UIAlertView, I wrote the following code


    UIAlertView *alert = [[UIAlertView alloc] initWithFrame:CGRectMake(0, 0, 300, 200)];
    
    alert.title = @"Preferences";
    alert.message = @"\n\n\n\n\n\n\n";
    alert.delegate = self;
    [alert addButtonWithTitle:@"Cancel"];
    [alert addButtonWithTitle:@"OK"];
    

    UIPickerView *myPickerView = [[UIPickerView alloc] initWithFrame:CGRectZero];
    myPickerView.delegate = self;
    myPickerView.showsSelectionIndicator = YES;
    myPickerView.autoresizingMask = UIAlertViewStyleDefault;
   
    myPickerView.frame = CGRectMake(10, 40, 250, 150);
    
    [alert addSubview:myPickerView];
    
    [alert show];

but when run, the pickerView size is not fit the alert view, it looks as shown in the image.

[here image][1]


how can I solve this issue? 
Thanks in advance.


  [1]: http://dt-works.com/emy/Screen%20Shot%202012-07-31%20at%2010.44.12%20AM.png