iOS生命周期 & 通知中心

浏览数：23 / 时间：2015年06月11日

笔记内容

学习笔记-段玉磊 Stanford course

View Controller Lifecycle

这篇文是我记载Developing iOS 7 Apps公开课 第5课的笔记

UITextView

Set its text and attributes via its NSMutableAttributedString

使用UITextView 要属性NSTextStorage类型

@property (nonatomic, readonly) NSTextStorage *textStorage;

NSTextStorage 是NSMutableAttributedString的一个子类
利用NSTextStorage更简洁的修改UITextView的更新，例如字体颜色。

View Controller Lifecycle

viewWillAppear 会被多次调用, 主要用于数据同步，例如离开了这个View，之后重新开启的时候，数据会重新加载，保证视图内的数据是最新的数据。

- (void)viewWillAppear:(BOOL)animated;

适用于对不可见的内容进行同步。例如一些网络同步最好在这里调用，如果在viewdidload 里面调用的话，一旦视图内容过大没有出现，则会造成网络无法加载成功。

viewWillDisappear主用用于动画的停止，释放View中的对象
viewDidDisappear 释放内存，将对象置nil.
awakeFromNib 是storyboard的方法，里面的函数运行在MVC被加载之前。
viewWillLayoutSubviews 布局改变的时候调用，例如横竖屏切换的时候

NSNotification

添加一个通知中心：

声明一个通知中心： [NSNotificationCenter defaultCenter]

通知中心开启监听方法：

-(void)addObserver:(id)observer // you (the object to get notified)
    selector:(SEL)methodToInvokeIfSomethingHappens
    name:(NSString *)name // name of station (a constant somewhere)
    object:(id)sender; // whose changes you’re interested in (nil is anyone’s)

当收到广播的时候，会触发这个方法：

-(void)methodToInvokeIfSomethingHappens:(NSNotification *)notification
{
    notification.name // the name passed above
    notification.object // the object sending you the notification 
    notification.userInfo // notification-specific information about what happened
}

如果要手动发送信息的话利用：

NSString *model=@"测试";
[[NSNotificationCenter defaultCenter] postNotificationName:@"Levi" 
object:model];

附上利用通知中心监听UITextView字体大小的源代码：

//
//  AttributorViewController.m
//  Attributor
//
//  Created by YuLei on 14-6-23.
//  Copyright (c) 2014年 ___DuanYuLei___. All rights reserved.
//

#import "AttributorViewController.h"

@interface AttributorViewController ()
@property (weak, nonatomic) IBOutlet UITextView *body;
@property (weak, nonatomic) IBOutlet UILabel *headline;
@property (weak, nonatomic) IBOutlet UIButton *outlineButton;

@end

@implementation AttributorViewController
- (IBAction)changeBodySelectionColorToMatchBackgroundOfButton:(UIButton *)sender {
    [self.body.textStorage addAttribute:NSForegroundColorAttributeName
                                  value:sender.backgroundColor
                                  range:self.body.selectedRange];
}

- (IBAction)outlineBodySelection{
    [self.body.textStorage addAttributes:@{NSStrokeWidthAttributeName: @-3,
                                           NSStrokeColorAttributeName: [UIColor blackColor]}
                                   range:self.body.selectedRange];
}

- (IBAction)unoutlineBodySelection {
    [self.body.textStorage removeAttribute:NSStrokeWidthAttributeName
                                     range:self.body.selectedRange];
}


- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(preferdFontsChanged:)
                                                 name:UIContentSizeCategoryDidChangeNotification
                                               object:nil];
}

- (void)preferdFontsChanged:(NSNotification *)notification
{
    [self usePreferredFonts];
}

- (void)usePreferredFonts
{
    self.body.font = [UIFont preferredFontForTextStyle:UIFontTextStyleBody];
    self.headline.font = [UIFont preferredFontForTextStyle:UIFontTextStyleHeadline];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    [self usePreferredFonts];
    [[NSNotificationCenter defaultCenter] removeObserver:self
                                                    name:UIContentSizeCategoryDidChangeNotification object:nil];
}


- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSMutableAttributedString *title = [[NSMutableAttributedString alloc] initWithString:self.outlineButton.currentTitle];
    [title setAttributes:@{NSStrokeWidthAttributeName: @3,
                           NSStrokeColorAttributeName: self.outlineButton.tintColor} range:NSMakeRange(0, [title length])];
    [self.outlineButton setAttributedTitle:title forState:UIControlStateNormal];
}


@end