WebView的使用

1、使用UIWebView加载网页

运行XCode 4.3，新建一个Single View Application，命名为WebViewDemo。

[img]

[/img]



2、加载WebView

在ViewController.h添加WebView成员变量和在ViewController.m添加实现

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController
{
    UIWebView *webView;
}
@end

- (void)viewDidLoad
{
    [super viewDidLoad];
    webView = [[UIWebView alloc] initWithFrame:CGRectMake(0, 0, 320, 480)];
    NSURLRequest *request =[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.baidu.com"]];
    [self.view addSubview: webView];
    [webView loadRequest:request];
}

运行，这样百度网页就打开了
[img]

[/img]




手机的网络环境是实时变化的，网络慢的时候，怎么提示用户网页正在打开呢？在网页打开出错的时候怎么提示用户呢？这时候我们就需要知道网页什么时候打开的，

什么时候加载完成，什么时候出错了。那么我们需要实现这个<UIWebViewDelegate>协议

3、实现协议，在ViewController.h修改如下：

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<UIWebViewDelegate>
{
    UIWebView *webView;
}
@end

按住control+command+向上键，切换到ViewController.m文件，这是我们在文件中打入- (void) webView，就能看到如下实现方法：

[img]

[/img]


UIWebView中几个重要的函数
1.- (void )webViewDidStartLoad:(UIWebView  *)webView   网页开始加载的时候调用
2.- (void )webViewDidFinishLoad:(UIWebView  *)webView  网页加载完成的时候调用
3.- (void)webView:(UIWebView *)webView  didFailLoadWithError:(NSError *)error 网页加载错误的时候调用



4、实现这三个方法，加入NSLog。

先在viewDidLoad 的webView实例化下面加上

    [webView setDelegate:self];设置代理。这样上面的三个方法才能得到回调。

三个方法实现如下：

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

运行打印：

2012-06-23 15:20:29.728 WebViewDemo[1001:f803] webViewDidStartLoad

2012-06-23 15:20:29.991 WebViewDemo[1001:f803] webViewDidFinishLoad
那我们试试error情况，把wifi关掉，运行打印结果：

2012-06-23 15:23:58.939 WebViewDemo[1087:f803] webViewDidStartLoad

2012-06-23 15:23:59.016 WebViewDemo[1087:f803] webViewDidFinishLoad

请求结果不变，为什么关掉网络还成功了呢？缓存？我换163.com试试，这是真正的结果出来了：

2012-06-23 15:24:41.131 WebViewDemo[1134:f803] webViewDidStartLoad

2012-06-23 15:24:41.149 WebViewDemo[1134:f803] didFailLoadWithError:Error Domain=NSURLErrorDomain Code=-1009 "The Internet connection appears to be offline." UserInfo=0x6b41660 {NSErrorFailingURLStringKey=http://www.163.com/, NSErrorFailingURLKey=http://www.163.com/, NSLocalizedDescription=The Internet connection appears to be offline., NSUnderlyingError=0x6eae690 "The Internet connection appears to be offline."}
连接错误了，调用了didFailLoadWithError。



5、加载等待界面

为了给用户更直观的界面效果，我们加上等待的loading界面试试

在webViewDidStartLoad加入等待

- (void) webViewDidStartLoad:(UIWebView *)webView
{
    //创建UIActivityIndicatorView背底半透明View     
    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 480)];  
    [view setTag:108];  
    [view setBackgroundColor:[UIColor blackColor]];  
    [view setAlpha:0.5];  
    [self.view addSubview:view];  
    
    activityIndicator = [[UIActivityIndicatorView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 32.0f, 32.0f)];  
    [activityIndicator setCenter:view.center];  
    [activityIndicator setActivityIndicatorViewStyle:UIActivityIndicatorViewStyleWhite];  
    [view addSubview:activityIndicator];  

    [activityIndicator startAnimating];
}

加载完成或失败时，去掉loading效果

- (void) webViewDidFinishLoad:(UIWebView *)webView
{
    [activityIndicator stopAnimating];
    UIView *view = (UIView*)[self.view viewWithTag:108];
    [view removeFromSuperview];
    NSLog(@"webViewDidFinishLoad");

}
- (void) webView:(UIWebView *)webView didFailLoadWithError:(NSError *)error
{
    [activityIndicator stopAnimating];
    UIView *view = (UIView*)[self.view viewWithTag:108];
    [view removeFromSuperview];
}

运行效果：
[img]

[/img]

补充：加载本地的html文件

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
	// Do any additional setup after loading the view, typically from a nib.
    UIWebView *webView = [[[UIWebView alloc] initWithFrame:CGRectMake(0, 100, 320, 360)] autorelease];
    
    //使用loadHTMLString()方法显示网页内容
    [webView loadHTMLString:[self getHtmlString] baseURL:nil];

    [self.view addSubview:webView];
}
    //读取html文件内容
- (NSString *)getHtmlString{
    //文件路径
    NSString *filePath = [[NSBundle mainBundle] pathForResource:@"index" ofType:@"html"];
    
    NSString *contents = [NSString stringWithContentsOfFile:filePath encoding:NSUTF8StringEncoding error:nil];
    return contents;
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

@end