Question

android loaddatawithbaseurl 和loadurl的区别

Answer 1

在开发Android平台的互联网应用时，经常会使用到WebView，好处主要有两个，一是可以更改要展现的内容（包括样式），二是可以实现部分功能的跨平台。

Android的WebView组件使用非常简单，可以使用loadUrl()加载一个Url地址，也可以使用loadData()或 loadDataWithBaseURL()加载一段HTML代码片段。loadUrl()的使用大家应该都没有什么问题，但是loadData()和 loadDataWithBaseURL()在使用上的差异可能有些人还不太清楚。
首先，从方法的定义来看：
public void loadData (String data, String mimeType, String encoding)
public void loadDataWithBaseURL (String baseUrl, String data, String mimeType, String encoding, String historyUrl)
loadDataWithBaseURL()比loadData()多两个参数，可以指定HTML代码片段中相关资源的相对根路径，也可以指定历史Url。两个方法的其余三个参数相同。

其次，两个方法加载的HTML代码片段有些不同，loadData()中的html data中不能包含'#', '%', '\', '?'四中特殊字符，这就为我们内嵌css等制造了些许麻烦，因为css中经常用'#', '%'等字符，需要如何处理呢？我们需要用UrlEncoder编码为%23, %25, %27, %3f 。
/**
* Loads the given data into this WebView using a 'data' scheme URL.
* <p>
* Note that JavaScript's same origin policy means that script running in a
* page loaded using this method will be unable to access content loaded
* using any scheme other than 'data', including 'http(s)'. To avoid this
* restriction, use {@link
* #loadDataWithBaseURL(String,String,String,String,String)
* loadDataWithBaseURL()} with an appropriate base URL.
* <p>
* If the value of the encoding parameter is 'base64', then the data must
* be encoded as base64. Otherwise, the data must use ASCII encoding for
* octets inside the range of safe URL characters and use the standard %xx
* hex encoding of URLs for octets outside that range. For example,
* '#', '%', '\', '?' should be replaced by %23, %25, %27, %3f respectively.
* <p>
* The 'data' scheme URL formed by this method uses the default US-ASCII
* charset. If you need need to set a different charset, you should form a
* 'data' scheme URL which explicitly specifies a charset parameter in the
* mediatype portion of the URL and call {@link #loadUrl(String)} instead.
* Note that the charset obtained from the mediatype portion of a data URL
* always overrides that specified in the HTML or XML document itself.
*
* @param data a String of data in the given encoding
* @param mimeType the MIME type of the data, e.g. 'text/html'
* @param encoding the encoding of the data
*/
public void loadData(String data, String mimeType, String encoding) {
checkThread();
mProvider.loadData(data, mimeType, encoding);
}
/**
* Loads the given data into this WebView, using baseUrl as the base URL for
* the content. The base URL is used both to resolve relative URLs and when
* applying JavaScript's same origin policy. The historyUrl is used for the
* history entry.
* <p>
* Note that content specified in this way can access local device files
* (via 'file' scheme URLs) only if baseUrl specifies a scheme other than
* 'http', 'https', 'ftp', 'ftps', 'about' or 'javascript'.
* <p>
* If the base URL uses the data scheme, this method is equivalent to
* calling {@link #loadData(String,String,String) loadData()} and the
* historyUrl is ignored.
*
* @param baseUrl the URL to use as the page's base URL. If null defaults to
* 'about:blank'.
* @param data a String of data in the given encoding
* @param mimeType the MIMEType of the data, e.g. 'text/html'. If null,
* defaults to 'text/html'.
* @param encoding the encoding of the data
* @param historyUrl the URL to use as the history entry. If null defaults
* to 'about:blank'.
*/
public void loadDataWithBaseURL(String baseUrl, String data,
String mimeType, String encoding, String historyUrl) {
checkThread();
mProvider.loadDataWithBaseURL(baseUrl, data, mimeType, encoding, historyUrl);
}