WebView Memory Management

An application that I am developing retains several WebViews that are used to allow an embedded web browsing experience for some activities centralized around the application. The problem that I am having is that after several hours open and after a lot of use the views begin to build up memory. My understanding of the memory management in Objective-C is that once and object is released entirely (retain count = 0) and is deallocated the amount of memory used by the application as a whole goes down. This does not seem to be applying to my situation.

[webviewObject release];
webviewObject = nil;

webviewObject = [[self createNewViewWithName:name] retain];

The above is 开发者_如何学Gothe code that I am using. I have tried releasing the memory and not creating a new instance but to no luck. Memory usage simply continues to grow and according to Instruments the objects are released entirely. Am I missing something? Could the application be caching some how?

I had a similar issue in a web view in one of my apps. Seems that there's some memory leak with web views in iphone SDK. My app crashed when there was a large text in the web view, and some other issues. This code helped me prevent memory leak. I hope that works for you, too.

Here's the instructions from that link:

Preventing memory leaks related to UIWebView can be difficult. Apple’s documentation on the subject is sparse, and not straight forward, simply because the UIWebView is a complex beast with many underlying classes used within. This Objective-C Category represents a collection of ideas, and theories (think magic rather than science..) collected from various web blogs and discussions on the subject. For more Objective-C memory management ideas, check out WIJL: IOS Memory Management. Using the Category is simple:

Download the code: UIWebView+Clean.zip

1. Add the UIWebView+Clean.h and .m files to your project.
2. Import UIWebView+Clean.h in any files you want to use the category in.
3. Use the cleanForDealloc method anywhere you intend to deallocate a UIWebView:

[self.webView cleanForDealloc];
self.webView = nil;

This is UIWebView+Clean.h:

/*

    UIWebView+Clean.h

    A simple category that performs recommended UIWebView clean before dealloc

    Created by Jason Baker (jason@onejasonforsale.com) for TumbleOn on 3/18/12.

    Copyright (c) 2012, Pocket Sized Giraffe, LLC
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice, this
    list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright notice,
    this list of conditions and the following disclaimer in the documentation
    and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
    ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
    WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
    DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
    ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
    (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
    ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
    SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

    The views and conclusions contained in the software and documentation are those
    of the authors and should not be interpreted as representing official policies,
    either expressed or implied.

 */

#import <Foundation/Foundation.h>

@interface UIWebView (clean)

// performs various cleanup activities recommended for UIWebView before dealloc.
// see comments in implementation for usage examples
- (void) cleanForDealloc;

@end

And this is UIWebView+Clean.m:

/*

 UIWebView+Clean.h

 A simple category that performs recommended UIWebView clean before dealloc

 Created by Jason Baker (jason@onejasonforsale.com) for TumbleOn on 3/18/12.

 Copyright (c) 2012, Pocket Sized Giraffe, LLC
 All rights reserved.

 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:

 1. Redistributions of source code must retain the above copyright notice, this
 list of conditions and the following disclaimer.
 2. Redistributions in binary form must reproduce the above copyright notice,
 this list of conditions and the following disclaimer in the documentation
 and/or other materials provided with the distribution.

 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 The views and conclusions contained in the software and documentation are those
 of the authors and should not be interpreted as representing official policies,
 either expressed or implied.

 */

#import "UIWebView+Clean.h"

@implementation UIWebView (clean)

/*

 Using this Category is easy, simply add this to the top of your file where
 you have a UIWebView:

 #import "UIWebView+Clean.h"

 Then, any time you want to throw away or deallocate a UIWebView instance, do
 the following before you throw it away:

 [self.webView cleanForDealloc];
 self.webView = nil;

 If you still have leak issues, read the notes at the bottom of this class,
 they  may help you.

 */


- (void) cleanForDealloc
{
    /*

     There are several theories and rumors about UIWebView memory leaks, and how
     to properly handle cleaning a UIWebView instance up before deallocation. This
     method implements several of those recommendations.

     #1: Various developers believe UIWebView may not properly throw away child
     objects & views without forcing the UIWebView to load empty content before
     dealloc.

     Source: http://stackoverflow.com/questions/648396/does-uiwebview-leak-memory

     */        
    [self loadHTMLString:@"" baseURL:nil];

    /*

     #2: Others claim that UIWebView's will leak if they are loading content
     during dealloc.

     Source: http://stackoverflow.com/questions/6124020/uiwebview-leaking

     */
    [self stopLoading];

    /*

     #3: Apple recommends setting the delegate to nil before deallocation:
     "Important: Before releasing an instance of UIWebView for which you have set
     a delegate, you must first set the UIWebView delegate property to nil before
     disposing of the UIWebView instance. This can be done, for example, in the
     dealloc method where you dispose of the UIWebView."

     Source: UIWebViewDelegate class reference    

     */
    self.delegate = nil;


    /*

     #4: If you're creating multiple child views for any given view, and you're
     trying to deallocate an old child, that child is pointed to by the parent
     view, and won't actually deallocate until that parent view dissapears. This
     call below ensures that you are not creating many child views that will hang
     around until the parent view is deallocated.
     */

    [self removeFromSuperview];

    /*

     Further Help with UIWebView leak problems:

     #1: Consider implementing the following in your UIWebViewDelegate:

     - (void) webViewDidFinishLoad:(UIWebView *)webView
     {
        //source: http://blog.techno-barje.fr/post/2010/10/04/UIWebView-secrets-part1-memory-leaks-on-xmlhttprequest/
        [[NSUserDefaults standardUserDefaults] setInteger:0 forKey:@"WebKitCacheModelPreferenceKey"];
     }

     #2: If you can, avoid returning NO in your UIWebViewDelegate here:

     - (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
     {
        //this source says don't do this: http://stackoverflow.com/questions/6421813/lots-of-uiwebview-memory-leaks
        //return NO;
        return YES;
     }

     #3: Some leaks appear to be fixed in IOS 4.1
     Source: http://stackoverflow.com/questions/3857519/memory-leak-while-using-uiwebview-load-request-in-ios4-0

     #4: When you create your UIWebImageView, disable link detection if possible:        

     webView.dataDetectorTypes = UIDataDetectorTypeNone;

     (This is also the "Detect Links" checkbox on a UIWebView in Interfacte Builder.)

     Sources:
     http://www.iphonedevsdk.com/forum/iphone-sdk-development/46260-how-free-memory-after-uiwebview.html
     http://www.iphonedevsdk.com/forum/iphone-sdk-development/29795-uiwebview-how-do-i-stop-detecting-links.html
     http://blog.techno-barje.fr/post/2010/10/04/UIWebView-secrets-part2-leaks-on-release/

     #5: Consider cleaning the NSURLCache every so often:

     [[NSURLCache sharedURLCache] removeAllCachedResponses];
     [[NSURLCache sharedURLCache] setDiskCapacity:0];
     [[NSURLCache sharedURLCache] setMemoryCapacity:0];

     Source: http://blog.techno-barje.fr/post/2010/10/04/UIWebView-secrets-part2-leaks-on-release/

     Be careful with this, as it may kill cache objects for currently executing URL
     requests for your application, if you can't cleanly clear the whole cache in
     your app in some place where you expect zero URLRequest to be executing, use
     the following instead after you are done with each request (note that you won't
     be able to do this w/ UIWebView's internal request objects..):

     [[NSURLCache sharedURLCache] removeCachedResponseForRequest:request];

     Source: http://stackoverflow.com/questions/6542114/clearing-a-webviews-cache-for-local-files  

     */
}

@end