UIWebView: delegate will not be called

I am trying to calculate the size of a UIWebView with given content, but not showing the view. I only need to know the size.

My problem: when I execute the code, the UIWebView delegate is not called. Why?

MessageSizeCaluclator.h

#import < Foundation/Foundation.h>

@class Message;

@interface MessageSizeCaluclator : NSObject <UIWebViewDelegate>

- (id)initWithMessage:(Message*)message;
- (void)saveSize;

@end

MessageSizeCaluclator.m

#import "Message.h"
#import "MessageSizeCaluclator.h"


@interface MessageSizeCaluclator () <UIWebViewDelegate>

@property (strong, nonatomic) Message* message;
@property (strong, nonatomic) UIWebView* webView;

@end


@implementation MessageSizeCaluclator

@synthesize message = _message;
@synthesize webView = _webView;


- (id)initWithMessage:(Message*)message
{
self = [super init];

if (self) {
    _message = message;

    // WebView
    _webView = [[UIWebView alloc] initWithFrame:CGRectMake(0, 0, 10, 10)];
    _webView.delegate = self;
}

return self;
}

- (void)saveSize
{
NSLog(@"%s message = %@", __PRETTY_FUNCTION__, _message.text);

[_webView loadHTMLString:[NSString stringWithFormat:@"<div style='font-family:Helvetica;font-size:13px;'>This is a test</div>", _message.text]
                                 baseURL:nil];
}

#pragma mark - Web view delegate

- (void)webView:(UIWebView *)webView didFailLoadWithError:(NSError *)error
{
NSLog(@"%s", __PRETTY_FUNCTION__);
}

- (void)webViewDidStartLoad:(UIWebView *)webView
{
NSLog(@"%s", __PRETTY_FUNCTION__);
}

- (void)webViewDidFinishLoad:(UIWebView *)webView
{
NSLog(@"%s", __PRETTY_FUNCTION__);
}

@end

Implementation

    MessageSizeCaluclator* messageSizeCalculator = [[MessageSizeCaluclator alloc] initWithMessage:message];
    [messageSizeCalculator saveSize];