问题解决

- (id) previewController: (QLPreviewController *) controller previewItemAtIndex: (NSInteger) index

{

if ([self.fileURL.lastPathComponent rangeOfString:@".txt"].location != NSNotFound) {

//处理txt格式内容显示有乱码的情况

NSData *fileData = [NSData dataWithContentsOfURL:self.fileURL];

//判断是UNICODE编码

NSString *isUNICODE = [[NSString alloc] initWithData:fileData encoding:NSUTF8StringEncoding];

//还是ANSI编码（-2147483623，-2147482591，-2147482062，-2147481296）encoding 任选一个就可以了

NSString *isANSI = [[NSString alloc] initWithData:fileData encoding:-2147483623];

if (isUNICODE) {

NSString *retStr = [[NSString alloc]initWithCString:[isUNICODE UTF8String] encoding:NSUTF8StringEncoding];

NSData *data = [retStr dataUsingEncoding:NSUTF16StringEncoding];

[data writeToURL:self.fileURL atomically:YES];

}else if(isANSI){

NSData *data = [isANSI dataUsingEncoding:NSUTF16StringEncoding];

[data writeToURL:self.fileURL atomically:YES];

}

}

return self.fileURL;

}