这段代码由 CocoaChina 会员 “xiaoyaoa” 分享，textField 为空时让按钮不可用，既防止误操作又显得应用很注重细节。
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range
replacementString:(NSString *)string
{
NSMutableString *newValue = [[self.TextField.text mutableCopy] autorelease];
[newValue replaceCharactersInRange:range withString:string];
if ([newValue length]== 0) {
self.navigationItem.rightBarButtonItem.enabled = NO;
}
else {
self.navigationItem.rightBarButtonItem.enabled = YES;
}
return YES;
}
- (BOOL)textFieldShouldClear:(UITextField *)textField{
self.navigationItem.rightBarButtonItem.enabled = NO;
return YES;
}