iOS定制NSURLProtocol实现离线缓存

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iOS如果直接用UIWebView直接加载网页，这种方法实现网页浏览最简单，理论上是没什么问题的。然而实际生产开发中，会碰到需要问题，比如：

网页图片太多响应慢
手机网络不好响应慢
网页前端Javascript插件太多响应慢
服务器并发高压力大响应慢
......

很多问题都会导致网页加载响应慢。所以就引出本文的主题，利用离线缓存优化加载流程，提升用户体验，同时可以一定程度上分散服务器压力。

iOS提供了个非常强大的功能给我们 —— NSURLProtocol

其强大之处在于可以拦截请求，然后自定义Response返回给UIWebView！

实现步骤

添加一个webview

WebViewController.h

//
//  WebViewController.h
//  demo
//
//  Created by Broly on 16/4/20.
//  Copyright © 2016年 Broly. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface WebViewController : UIViewController

@property (weak, nonatomic) IBOutlet UIWebView *webView;

@end

// WebViewController.h

// demo

// Created by Broly on 16/4/20.

#import <UIKit/UIKit.h>

@interface WebViewController : UIViewController

@property (weak, nonatomic) IBOutlet UIWebView *webView;

@end

WebViewController.m

//
//  WebViewController.m
//  demo
//
//  Created by Broly on 16/4/20.
//  Copyright © 2016年 Broly. All rights reserved.
//

#import "WebViewController.h"
#import "CustomURLProtocol.h"

@interface WebViewController () <UIWebViewDelegate>

@end

@implementation WebViewController

@synthesize webView = _webView;

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    // 重要!! 注册自定义的CustomURLProtocol
    [NSURLProtocol registerClass:[CustomURLProtocol class]];
    
    self.webView.delegate = self;
    
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    // document目录下有个demo文件夹，放置缓存文件
    NSString *path = [[paths objectAtIndex:0] stringByAppendingString:@"/demo"];
    
    // 指定基础url路径
    NSURL *baseURL = [NSURL fileURLWithPath:path];
    NSString *htmlPath = [path stringByAppendingString:@"/index.html"];
    NSString *htmlCont = [NSString stringWithContentsOfFile:htmlPath
                                                    encoding:NSUTF8StringEncoding
                                                       error:nil];
    NSLog(@"%@", htmlPath);
    // 加载本地index.html，当然也可以加载远程网页
    [self.webView loadHTMLString:htmlCont baseURL:baseURL];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType{
    NSLog(@"shouldStartLoadWithRequest");
    return YES;
}

- (void)webViewDidStartLoad:(UIWebView *)webView{
    NSLog(@"webViewDidStartLoad");
}

- (void)webViewDidFinishLoad:(UIWebView *)webView{
    NSLog(@"webViewDidFinishLoad");
}

- (void)webView:(UIWebView *)webView didFailLoadWithError:(nullable NSError *)error{
    NSLog(@"didFailLoadWithError");
}


/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/

@end

// WebViewController.m

// demo

// Created by Broly on 16/4/20.

#import "WebViewController.h"

#import "CustomURLProtocol.h"

@interface WebViewController () <UIWebViewDelegate>

@end

@implementation WebViewController

@synthesize webView = _webView;

- (void)viewDidLoad {

[super viewDidLoad];

// Do any additional setup after loading the view.

// 重要!! 注册自定义的CustomURLProtocol

[NSURLProtocol registerClass:[CustomURLProtocol class]];

self.webView.delegate = self;

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

// document目录下有个demo文件夹，放置缓存文件

NSString *path = [[paths objectAtIndex:0] stringByAppendingString:@"/demo"];

// 指定基础url路径

NSURL *baseURL = [NSURL fileURLWithPath:path];

NSString *htmlPath = [path stringByAppendingString:@"/index.html"];

NSString *htmlCont = [NSString stringWithContentsOfFile:htmlPath

encoding:NSUTF8StringEncoding

error:nil];

NSLog(@"%@", htmlPath);

// 加载本地index.html，当然也可以加载远程网页

[self.webView loadHTMLString:htmlCont baseURL:baseURL];

}

- (void)didReceiveMemoryWarning {

[super didReceiveMemoryWarning];

// Dispose of any resources that can be recreated.

}

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType{

NSLog(@"shouldStartLoadWithRequest");

return YES;

}

- (void)webViewDidStartLoad:(UIWebView *)webView{

NSLog(@"webViewDidStartLoad");

}

- (void)webViewDidFinishLoad:(UIWebView *)webView{

NSLog(@"webViewDidFinishLoad");

}

- (void)webView:(UIWebView *)webView didFailLoadWithError:(nullable NSError *)error{

NSLog(@"didFailLoadWithError");

}

#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {

// Get the new view controller using [segue destinationViewController].

// Pass the selected object to the new view controller.

}

@end

2. 添加自定义的NSURLProtocol

CustomURLProtocol.h

//
//  CustomURLProtocol.h
//  demo
//
//  Created by Broly on 16/4/21.
//  Copyright © 2016年 Broly. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface CustomURLProtocol : NSURLProtocol

@end

// CustomURLProtocol.h

// demo

// Created by Broly on 16/4/21.

#import <Foundation/Foundation.h>

@interface CustomURLProtocol : NSURLProtocol

@end

CustomURLProtocol.m

//
//  CustomURLProtocol.m
//  demo
//
//  Created by Broly on 16/4/21.
//  Copyright © 2016年 Broly. All rights reserved.
//

#import "CustomURLProtocol.h"

@implementation CustomURLProtocol

+ (BOOL)canInitWithRequest:(NSURLRequest *)request {
    return [[[request URL] scheme] isEqualToString:@"file"]; // 这里是重点，定义拦截的规则，比如以XXX结尾的，或者XXX开头的都可以
}

+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request {
    return request;
}

- (void) startLoading {
    // 这里可以自定义Response返回
    id<NSURLProtocolClient> client = [self client];
    NSURLRequest* request = [self request];
    NSString *pathString = [[request URL] absoluteString];
    
    NSString *fileName = [pathString lastPathComponent];
    
    NSString *fileToLoad = nil;
    fileToLoad = [pathString substringFromIndex:7];
    NSLog(@"%@\n%@", pathString, fileToLoad);

    NSData *data = [NSData dataWithContentsOfFile:fileToLoad];
    
    NSHTTPURLResponse* response = [[NSHTTPURLResponse alloc] initWithURL:[request URL] statusCode:200 HTTPVersion:@"HTTP/1.1" headerFields:[NSDictionary dictionary]];
    
    [client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
    [client URLProtocol:self didLoadData:data];
    [client URLProtocolDidFinishLoading:self];
}

- (void) stopLoading {}

@end

// CustomURLProtocol.m

// demo

// Created by Broly on 16/4/21.

#import "CustomURLProtocol.h"

@implementation CustomURLProtocol

+ (BOOL)canInitWithRequest:(NSURLRequest *)request {

return [[[request URL] scheme] isEqualToString:@"file"]; // 这里是重点，定义拦截的规则，比如以XXX结尾的，或者XXX开头的都可以

}

+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request {

return request;

}

- (void) startLoading {

// 这里可以自定义Response返回

id<NSURLProtocolClient> client = [self client];

NSURLRequest* request = [self request];

NSString *pathString = [[request URL] absoluteString];

NSString *fileName = [pathString lastPathComponent];

NSString *fileToLoad = nil;

fileToLoad = [pathString substringFromIndex:7];

NSLog(@"%@\n%@", pathString, fileToLoad);

NSData *data = [NSData dataWithContentsOfFile:fileToLoad];

NSHTTPURLResponse* response = [[NSHTTPURLResponse alloc] initWithURL:[request URL] statusCode:200 HTTPVersion:@"HTTP/1.1" headerFields:[NSDictionary dictionary]];

[client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];

[client URLProtocol:self didLoadData:data];

[client URLProtocolDidFinishLoading:self];

}

- (void) stopLoading {}

@end

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实现步骤

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