键盘遮挡

//开始编辑输入框的时候，软键盘出现，执行此事件
-(void)textFieldDidBeginEditing:(UITextField *)textField
{
    int offset = self.view.frame.size.height - textField.frame.origin.y - textField.frame.size.height - 246-30;//键盘高度216
    
    NSTimeInterval animationDuration = 0.30f;
    [UIView beginAnimations:@"ResizeForKeyboard" context:nil];
    [UIView setAnimationDuration:animationDuration];
    
    //将视图的Y坐标向上移动offset个单位，以使下面腾出地方用于软键盘的显示
    if(offset < 0)
        self.view.frame = CGRectMake(0.0f, offset, self.view.frame.size.width, self.view.frame.size.height);
    
    [UIView commitAnimations];
}

//当用户按下return键或者按回车键，keyboard消失
-(BOOL)textFieldShouldReturn:(UITextField *)textField
{
    [textField resignFirstResponder];
    return YES;
}

//输入框编辑完成以后，将视图恢复到原始状态
-(void)textFieldDidEndEditing:(UITextField *)textField
{
    self.view.frame =CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height);
}