我尝试用程序创建HTML文件。但生成的文件显示我为空白文件。我不知道这个问题。
这是我的代码：
- (IBAction) createFileAction
{
NSLog(@"************* createFileAction *************");
NSMutableString *htmlString = [[NSMutableString alloc] init];
NSLog(@"%@",htmlString);
[htmlString appendString:@"<html><head><title></title><style type='text/css'>.style1{height: 27px;}#Text1{height: 19px;width: 210px;}.style2{width: 255px;}.style3{height: 27px;width: 255px;}#petValue{width: 206px;}#nameValue{width: 206px;}#dateValue{width: 209px;}"];
[htmlString appendString:@"#Text2{width: 215px;}#Text3{width: 210px;height: 22px;}#Text4{width: 209px;}.style8{width: 13px;}.style9{ width: 263px;}.style10{height: 27px;width: 263px;}"];
[htmlString appendString:@".style11{width: 418px;}.style12{width: 199px;}.style13{height: 27px; width: 199px;}.style14{height: 24px;}.style15{width: 410px;}</style> </head>"];
[htmlString appendString:@"<body>"];
NSString *originalString = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://www.makepartsfast.com/2012/09/4337/more-3d-printing-in-metals-ex-one-introduces-the-m-flex-3d-printing-system/"] encoding:NSUTF8StringEncoding error:nil];
NSScanner *scanner = [NSScanner scannerWithString:originalString];
NSString *extractedString = nil;
[scanner scanUpToString:@"<div class="postarea">" intoString:nil];
[scanner scanString:@"<div class="postarea">" intoString:nil];
[scanner scanUpToString:@"<div style="clear:both;">" intoString:&extractedString];
if (extractedString)
{
// string was extracted
NSLog(@"%@", extractedString);
}
NSLog(@"BEFORE= %@",htmlString);
[htmlString appendString:extractedString];
NSLog(@"AFTER= %@",htmlString);
[htmlString appendString:@"</body></html>"];
NSLog(@"FINAL=%@",htmlString);
// check to see if file already exists in documents directory
if([self.fileMgr fileExistsAtPath:self.file])
{
NSLog(@"File already exists");
}
else
{
NSLog(@"file does not exist");
NSLog(@"Try creating the file");
// file does not already exist so create it
[self.fileMgr createFileAtPath:file contents:nil attributes:nil];
NSLog(@"%@",htmlString);
[htmlString writeToFile:self.file atomically:NO encoding:NSStringEncodingConversionAllowLossy error:nil];
//Test again whether this file exists now that we have tried creating it
if([self.fileMgr fileExistsAtPath:self.file])
{
NSLog(@"File exists now");
}
else
{
NSLog(@"File still doesn't exist");
}
}
}
在这个方法中，我只从extractedString中的html格式的URL中获得select部分；将其附加到htmlstring中。当我尝试附加不同的字符串时，它可以正常工作。
这是因为您将NSStringEncodingConversionAllowLossy作为encoding参数传递。您应该传递一个字符串编码参数。现在的情况是NSStringEncodingConversionAllowLossy等于1。但是writeToFile:atomically:encoding:error:需要一个字符串编码常量。等于1的字符串编码常数是NSASCIIStringEncoding。但是您的字符串无法转换为ASCII，因此会得到一个空文件。将该行更改为使用UTF8，就会得到预期的非空文件：
[htmlString writeToFile:self.file atomically:NO encoding:NSUTF8StringEncoding error:nil];
您遇到了问题，至少部分原因是您没有检查返回类型或错误条件。方法调用返回BOOL，如果出现任何问题，将创建一个NSError。如果你在听的话，这会帮助你找出问题所在。如果你这样做了：
NSError *saveError = nil;
if (![htmlString writeToFile:file atomically:NO encoding:NSStringEncodingConversionAllowLossy error:&saveError]) {
NSLog(@"Error writing file: %@", saveError);
}
你会看到一条错误消息，上面写着：
2012-11-21 11:20:47.250 Untitled[5731:707] Error writing file: Error Domain=NSCocoaErrorDomain Code=517 "The file “junk.html” couldn’t be saved using text encoding Western (ASCII)." UserInfo=0x7ffc0860b7c0 {NSFilePath=/tmp/junk.html, NSStringEncoding=1
这一点起初可能并不明显，但它特别提到尝试使用ASCII，这将是问题根源的重要线索。