IOS development: interaction between Objective-C and JavaScript

StringByEvaluatingJavaScriptFromString

To use the stringByEvaluatingJavaScriptFromString method, call the method after the page in UIWebView is loaded. We drag and drop a UIWebView control on the interface. Load googlemobile into this control. The Code is as follows:

 
 

  
  
- (void)viewDidLoad 
  
  
{ 
  
  
    [super viewDidLoad]; 
  
  
    webview.backgroundColor = [UIColor clearColor];   
  
  
    webview.scalesPageToFit =YES; 
  
  
    webview.delegate =self; 
  
  
    NSURL *url =[[NSURL alloc] initWithString:@"http://www.google.com.hk/m?gl=CN&hl=zh_CN&source=ihp"]; 
  
  
 
  
  
    NSURLRequest *request =  [[NSURLRequest alloc] initWithURL:url]; 
  
  
    [webview loadRequest:request];    
  
  
} 
 
 

We can use javascript to operate interface elements in the webViewDidFinishLoad method.

1. Obtain the url of the current page.

 
 

  
  
- (void)webViewDidFinishLoad:(UIWebView *)webView {   
  
  
  NSString *currentURL = [webView stringByEvaluatingJavaScriptFromString:@"document.location.href"]; 
  
  
} 
 
 

2. Obtain the page title:

 
 

  
  
- (void)webViewDidFinishLoad:(UIWebView *)webView {   
  
  
   NSString *currentURL = [webView stringByEvaluatingJavaScriptFromString:@"document.location.href"]; 
  
  
 
  
  
   NSString *title = [webview stringByEvaluatingJavaScriptFromString:@"document.title"];  
  
  
} 
 
 

3. Modify the value of the interface element.

 
 

  
  
NSString * js_result = [webView stringByEvaluatingJavaScriptFromString: @ "document. getElementsByName ('q') [0]. value = 'zhu Yulin ';"];
 
 

4. Form submission:

 
 

  
  
NSString *js_result2 = [webView stringByEvaluatingJavaScriptFromString:@"document.forms[0].submit(); "]; 
 
 

In this way, you can search for the keyword "Zhu Yulin" on google.

5. Insert js Code

The above functions can be encapsulated into a js function and inserted into the page for execution. The Code is as follows:

 
 

  
  
[WebView stringByEvaluatingJavaScriptFromString: @ "var script = document. createElement ('script ');"
  
  
"Script. type = 'text/javascript ';"
  
  
"Script. text = \" function myFunction (){"
  
  
"Var field = document. getElementsByName ('q') [0];"
  
  
"Field. value = 'zhu Yulin ';"
  
  
"Document. forms [0]. submit ();"
  
  
"}\";"
  
  
"Document. getElementsByTagName ('head') [0]. appendChild (script);"];
  
  

  
  
[WebView stringByEvaluatingJavaScriptFromString: @ "myFunction ();"];
 
 

Look at the above Code:

A. First, create a script tag using js. The type is 'text/javascript '.

B. Insert a string into the tag. This string is a function: myFunction, which enables google to automatically search for keywords.

C. Use stringByEvaluatingJavaScriptFromString to execute the myFunction.

Demo:

Step 1 open the google mobile website

Step 2 enter keywords

Step 3 search

Summary: This article mainly explains the usage of stringByEvaluatingJavaScriptFromString. It is very powerful and easy to use. Through it, we can easily operate the page elements in uiwebview.

Address: http://www.cnblogs.com/zhuqil/archive/2011/08/03/2126562.html