1.textfield的鍵盤類型：只能輸入數(shù)字和小數(shù)點
textField.keyboardType = UIKeyboardTypeDecimalPad;
2.注冊代理
textField.delegate = self;
3.在代理方法中控制：（1）首位不能輸入小數(shù)點；（2）只能輸入一個小數(shù)點；（3）小數(shù)點后最多輸入兩位。
-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
NSLog(@"string =%@==",string);

if ([string isEqualToString:@"."]&&(textField.text.length==0)) {
    return NO;
}  
if ([string isEqualToString:@"."]&&[textField.text containsString:@"."]) {
    return NO;
}
if (![string isEqualToString:@""]&&[textField.text containsString:@"."]) {
    
    NSArray *arr = [textField.text componentsSeparatedByString:@"."];
    if (arr.count == 2) {
        NSString *str = arr.lastObject;
        if (str.length>=2) {
            return NO;
        }
    }
}
return YES;

}