IOS代码布局（三） UITextField

（一）常规操作

　　1.定义一个UITextField，名为textField：

UITextField *textField = = [[UITextField alloc] initWithFrame:CGRectMake(10, 10, 200, 40)];

　　2.设置背景颜色

textField.backgroundColor = [UIColor colorWithRed:0.5 green:0.5 blue:0 alpha:0.5];

　　3.??????设置边框类型

textField.borderStyle = UITextBorderStyleRoundedRect; 

　　4.设置背景图片

textField???.background = [UIImage imageNamed:@""];

　　5.设置委托对象

textField.delegate = self;                                                   

　　6.设置默认提示文字

textField.placeholder = @"请输入文字";

　　7.弹出键盘（变成第一响应者）

[textField becomeFirstResponder];

　　8.文字内容 垂直居中

textField.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;

（二）委托设置

　　1.在声明中引入委托名（ ViewController.m中）

@interface ViewController ()<UITextFieldDelegate/*这里引入UITextField 需要的委托*/>{
    //在这里声明全局 私有变量
    UITextField *textField;
}

　　2.设置委托对象

textField.delegate = self;  

　　3.实现委托方法

//以下是UITextFieldDelegate 的部分委托实现
//*******************************************************************************
#pragma mark -------------------
#pragma mark UITextFieldDelegate

- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField{
    // return NO to disallow editing.
    return YES;
}
- (void)textFieldDidBeginEditing:(UITextField *)textField{
    // became first responder
    // 在这里监听UITextField becomeFirstResponder事件
}
- (BOOL)textFieldShouldEndEditing:(UITextField *)textField{
    // return YES to allow editing to stop and to resign first responder status. NO to disallow the editing session to end
    return YES;
}
- (void)textFieldDidEndEditing:(UITextField *)textField{
    // may be called if forced even if shouldEndEditing returns NO (e.g. view removed from window) or endEditing:YES called
    // 在这里监听UITextField resignFirstResponder事件
}
- (BOOL)textField:(UITextField *)_textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
    // return NO to not change text
    NSLog(@"inputText: %@", textField.text);
    return