关于UITextView使用及无法显示文本的解决方案。
首先说一下不显示的解决：
1.考虑编码格式
国际通用的是UTF-8,汉字的是GBK。另外，可以看下文档中NSStringEncoding的所有取值，其实不止这些，可以用代码输出所有编码格式，如下：
const NSStringEncoding *encodings = [NSString availableStringEncodings];
NSMutableString *str = [[NSMutableString alloc] init];
NSStringEncoding encoding;
while ((encoding = *encodings++) != 0){
[str appendFormat: @"%@ === %in", [NSString localizedNameOfStringEncoding：encoding], encoding];
}
NSLog(@"%@",str);
打印出所有支持的编码列表如下：
Western (Mac OS Roman) === 30
Japanese (Mac OS) === -2147483647
Traditional Chinese (Mac OS) === -2147483646
Korean (Mac OS) === -2147483645
Arabic (Mac OS) === -2147483644
Hebrew (Mac OS) === -2147483643
Greek (Mac OS) === -2147483642
Cyrillic (Mac OS) === -2147483641
Devanagari (Mac OS) === -2147483639
Gurmukhi (Mac OS) === -2147483638
Gujarati (Mac OS) === -2147483637
Thai (Mac OS) === -2147483627
Simplified Chinese (Mac OS) === -2147483623
Tibetan (Mac OS) === -2147483622
Central European (Mac OS) === -2147483619
Symbol (Mac OS) === 6
Dingbats (Mac OS) === -2147483614
Turkish (Mac OS) === -2147483613
Croatian (Mac OS) === -2147483612
Icelandic (Mac OS) === -2147483611
Romanian (Mac OS) === -2147483610
Celtic (Mac OS) === -2147483609
Gaelic (Mac OS) === -2147483608
Keyboard Symbols (Mac OS) === -2147483607
Farsi (Mac OS) === -2147483508
Cyrillic (Mac OS Ukrainian) === -2147483496
Inuit (Mac OS) === -2147483412
Unicode (UTF-32LE) === -1677721344
Unicode (UTF-8) === 4
Unicode (UTF-16) === 10
Unicode (UTF-16BE) === -1879047936
Unicode (UTF-16LE) === -1811939072
Unicode (UTF-32) === -1946156800
Unicode (UTF-32BE) === -1744830208
Western (ISO Latin 1) === 5
Central European (ISO Latin 2) === 9
Western (ISO Latin 3) === -2147483133
Central European (ISO Latin 4) === -2147483132
Cyrillic (ISO 8859-5) === -2147483131
Arabic (ISO 8859-6) === -2147483130
Greek (ISO 8859-7) === -2147483129
Hebrew (ISO 8859-8) === -2147483128
Turkish (ISO Latin 5) === -2147483127
Nordic (ISO Latin 6) === -2147483126
Thai (ISO 8859-11) === -2147483125
Baltic Rim (ISO Latin 7) === -2147483123
Celtic (ISO Latin 
===
-2147483122
Western (ISO Latin 9) === -2147483121
Romanian (ISO Latin 10) === -2147483120
Latin-US (DOS) === -2147482624
Greek (DOS) === -2147482619
Baltic Rim (DOS) === -2147482618
Western (DOS Latin 1) === -2147482608
Greek (DOS Greek 1) === -2147482607
Central European (DOS Latin 2) === -2147482606
Cyrillic (DOS) === -2147482605
Turkish (DOS) === -2147482604
Portuguese (DOS) === -2147482603
Icelandic (DOS) === -2147482602
Hebrew (DOS) === -2147482601
Canadian French (DOS) === -2147482600
Arabic (DOS) === -2147482599
Nordic (DOS) === -2147482598
Cyrillic (DOS) === -2147482597
Greek (DOS Greek 2) === -2147482596
Thai (Windows, DOS) === -2147482595
Japanese (Windows, DOS) === 8
Simplified Chinese (Windows, DOS) === -2147482591
Korean (Windows, DOS) === -2147482590
Traditional Chinese (Windows, DOS) === -2147482589
Western (Windows Latin 1) === 12
Central European (Windows Latin 2) === 15
Cyrillic (Windows) === 11
Greek (Windows) === 13
Turkish (Windows Latin 5) === 14
Hebrew (Windows) === -2147482363
Arabic (Windows) === -2147482362
Baltic Rim (Windows) === -2147482361
Vietnamese (Windows) === -2147482360
Western (ASCII) === 1
Japanese (Shift JIS X0213) === -2147482072
Chinese (GBK) === -2147482063
Chinese (GB 18030) === -2147482062
Japanese (ISO 2022-JP) === 21
Korean (ISO 2022-KR) === -2147481536
Japanese (EUC) === 3
Simplified Chinese (EUC) === -2147481296
Traditional Chinese (EUC) === -2147481295
Korean (EUC) === -2147481280
Japanese (Shift JIS) === -2147481087
Cyrillic (KOI8-R) === -2147481086
Traditional Chinese (Big 5) === -2147481085
Western (Mac Mail) === -2147481084
Simplified Chinese (HZ GB 2312) === -2147481083
Traditional Chinese (Big 5 HKSCS) === -2147481082
Ukrainian (KOI8-U) === -2147481080
Traditional Chinese (Big 5-E) === -2147481079
Western (NextStep) === 2
Non-lossy ASCII === 7
Western (EBCDIC Latin 1) === -2147480574
from:http://hi.baidu.com/may2150209/blog/item/198976ace7e583054b36d6f1.html
2.创建tv后做一个赋值tv = nil；
在苹果的developer library上UILable的text属性默认是nil，而UITextView却没提（有待考证）。
UITextView的使用：
首先说一下TextView键盘的退出，只需要一句：[textView resignFirstResponder];，至于退出的方式，网上看到三种(前两种需要使用UITextViewDelegate)：1.在导航条上加一个按钮。2.用键盘（手机上电脑上均适用）的回车键。3.在弹出的键盘上加一个UIView来放置退出键盘按钮。
具体实现可参考：http://wuchaorang.2008.blog.163.com/blog/static/48891852201232014813990/
还有自定义TextView内选取文字后弹出菜单的方法。
