使用MailCore创建iOS邮件客户端(三)
五、在webview中预览附件点击附件后，我们需要将附件下载到本地(tmp文件夹）并用在webview中预览它：
CTCoreAttachment* core_att=(CTCoreAttachment*)sender.tag;
NSString *ext=[core_att.decodedFilenamepathExtension];
NSString* temp=pathForTemporaryFile(ext);
[core_att writeToFile:temp];
// NSLog(@"charset:%@",core_att.charset);
[selfopenFile:temp attach:core_att];pathForTemporaryFile()函数用于在tmp文件夹下产生一个随机的临时文件名。然后用CTCoreAttachment的writeToFile:方法进行保存。当然，为了不丢失文件类型，我们必须在临时文件中保留原来的文件扩展名。然后调用openFile:attach:方法在webview中打开附件文件：-(void)openFile:(NSString*)tempFile attach:(CTCoreAttachment*)att{??previewVC* vc=[[previewVCalloc]init];
[self.navigationControllerpushViewController:vc animated:YES];
[vc openTemporaryFile:tempFile attach:att];
[vc release];}注意webview支持预览的文件相当多，我们用一个plist文件保存了它所支持的一些mime类型。但实际上还不止这么多：<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plistPUBLIC "-//Apple//DTDPLIST 1.0//EN""http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<array>
<string>text/plain</string>
<string>text/html</string>
<string>text/xml</string>
<string>image/tiff</string>
<string>image/png</string>
<string>image/x-icon</string>
<string>image/jpeg</string>
<string>image/pict</string>
<string>image/gif</string>
<string>image/bmp</string>
<string>application/pdf</string>
<string>application/msword</string>
<string>application/vnd.ms-excel</string>
<string>text/richtext</string>
</array>
</plist>previewVC中放了一个webview用于预览附件文件，它的openTemporaryFile:attach:方法实现如下：-(void)openTemporaryFile:(NSString *)temp attach:(CTCoreAttachment*)att{
self.title=att.decodedFilename;
NSString* contentType=att.contentType;
if (contentType && [contentType isEqualToString:@"text/plain"]) {
[selfopenTextFile:temp mimeType:contentType];
}else{
[webViewloadRequest:
[NSURLRequestrequestWithURL:
[NSURLfileURLWithPath:temp]]];
}
} 这个方法堆text/plain类型的文件（.txt、.text）进行特别处理。因为这类文件的字符集charset从文件名无法推断。一个.txt文件中的字符编码可能是任意的：utf-8、ascii，如果有中文，那么还可能是gb2312或者gbk的。因此在openTextFile:mimeType:方法中，我们先后尝试了utf-8、gbk和gb2312编码，如果都不正确，则采用us-ascii。最后用推断出的编码加载文件到webview：NSError* error=nil;
NSString* encoding;
// determine text encoding
NSString* content=[NSStringstringWithContentsOfFile:file
encoding:NSUTF8StringEncoding
error:&error];
if (error) {
error=nil;
content=[NSStringstringWithContentsOfFile:file
encoding:CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000)
error:&error];
if (error) {
error=nil;
// 0x0421 is kCFStringEncodingDOSChineseSimplifdeclared in CFStringEncodingExt.h,
// this hinted the codepage 936 which is gb2312 with a reference from IANA encoding
content=[NSStringstringWithContentsOfFile:file
encoding:CFStringConvertEncodingToNSStringEncoding(0x0421)
error:&error];
if (error)
encoding=@"us-ascii";
else
encoding=@"gb2312";
}else{
encoding=@"GB18030";
}
}else{
encoding=@"UTF-8";
}
[webViewloadData:[NSDatadataWithContentsOfFile:file]
MIMEType:type textEncodingName:encoding baseURL:nil]; 而且，我们使用了webview的loadData:MIMEType:textEncodingName:baseURL:方法，而不是一般的loadRequest:方法，否则对于中文text/plain文件，显示的是乱码。