用javascript唤起iOS和Android客户端

大部分pc到客户端引流都采用二维码扫描的方式，扫码这里就不说了，关键说一下如何从扫码到唤起客户端，暂时仅包括android和ios两大平台。

处理逻辑

1. 扫码到一个http页面
2. 页面上写javascript通过useragent判断当前平台android／iphone／ipad；
3. create一个隐藏的frame，设置他的src为应用注册的schema来唤起客户端，比如淘宝主客就是taobao://；
4. 如果用户没有安装客户端，再通过settimeout引导到客户端下载页；
5. 这里要特别注意android和ios一个最大的区别是android唤起的时间要比ios慢许多；比如ios只需要200ms就可以判断唤起，但是android起码要600ms，所以引导到客户端下载页的timeout要有所区别；

代码示例

	var noClientCallback = function(){
		window.location = “http://2.taobao.com/m.html”;
	};

	(function(){
		var outTime = (navigator.userAgent.match(/android/i))?600:200;
		var goUrl = “taobao://wnwebview?url=http://www.taobao.com/”;
		var e_frame = document.createElement(‘frame’);
		e_frame.setAttribute(‘id’, ‘J_smartFrame’);
		e_frame.style.cssText = ‘display:none’;
		document.body.appendChild(e_frame);
		e_frame.setAttribute(‘src’,goUrl);
		window.setTimeout(function(){
			if(e_frame){
				document.body.removeChild(e_frame);
			}
			noClientCallback();
		},outTime);
	})();

Android Update

最近发现部分android手机不能正常唤起客户端，主要原因google有解释：https://developer.chrome.com/multidevice/android/intents

也就是说现在Android的chrome下（25及以后的版本），上面的隐藏iframe方式不能正常生效了，唤起客户端需要这么写：

window.location = ‘intent://item/#Intent;scheme=taobao;package=com.taobao;end’;

如果还需要带一些参数的话，可以写在item后面

window.location = ‘intent://item?id=12345678/#Intent;scheme=taobao;package=com.taobao;end’;

另外如果还有唤起客户端的需要，建议看看这个repo：https://github.com/miaojing/redirectToNative

以及他的demo：http://gallery.kissyui.com/redirectToNative/1.2/demo/index.html

objective-c的class和metaclass

Class & id 的定义

首先看看在objective-c中对于class和object的定义，这个在/usr/include/objc/objc.h 和 runtime.h中可以找到：

typedef struct objc_class *Class;
typedef struct objc_object {
 	Class isa;
} *id;

class是一个objc_class的指针，id（也就是对象）是一个指向objc_object结构体的指针，所以每个对象都有一个纸箱class（objc_class）的isa指针；

objc_class 的定义

那么objc_class又是怎样的呢？

struct objc_class
{
	struct objc_class* isa;
    struct objc_class* super_class;
    const char* name;
    long version;
    long info;
	long instance_size;
    struct objc_ivar_list* ivars;
	struct objc_method_list** methodLists;
    struct objc_cache* cache;
    struct objc_protocol_list* protocols;
};

可以看到class又有一个指向class的isa指针，这个class就是我们俗称的metaclass，也就是类对象的isa指向的就是metaclass；

metaclass跟class的区别在于metaclass存储类static开头的方法和static开头的成员（+开头的方法）；class存储类的实例方法和实例变量（-开头的）；

这里应用一张别人的图来说明class、metaclass、superclass几者之间的关系就一目了然

1. 类的实例对象的isa指向类，类的isa指向类的metaclass，类的metaclass指向基类的metaclass
2. 类的superclass指向父类，类的metaclass的superclass指向该类的superclassmetaclass
3. 基类的superclass指向nil，基类的metaclass指向基类自己

说完了isa和superclass的关系，我们再说一下objc_class的其他属性

1. name：一个c字符串，指向类的名称。我们可以在运行期，通过这个名称查找到该类（通过：id objc_getClass(const char *aClassName)）或者该类的metaclass（id objc_getMetaClass(const char *aClassName)）
2. version：类的版本信息，默认初始化为0.我们可以在运行期对其进行修改（class_setVersion）或后去(class_getVersion)
3. info：标示类的类型，比如是metaclass还是class
4. instance_size：该类的实例变量大小
5. ivars：实例变量
6. methodLists：如果上面info说明当前是class，这里存储实例方法，如果是metaclass，这里存储类额静态方法
7. cache：指向objc_cache的指针，用于对方法的缓存
8. protocols：指向objc_protocol_list的指针，存储该类要遵守的协议

内容参考自：http://www.cnblogs.com/kesalin/archive/2012/01/19/objc_class_object.html

-layoutSubviews什么时候被调用

原文：http://blog.logichigh.com/2011/03/16/when-does-layoutsubviews-get-called/

So the results is below:

1. init does not cause layoutSubviews to be called (duh)
2. addSubview causes layoutSubviews to be called on the view being added, the view it’s being added to (target view), and all the subviews of the target view
3. setFrame intelligently calls layoutSubviews on the view having it’s frame set only if the size parameter of the frame is different
4. scrolling a UIScrollView causes layoutSubviews to be called on the scrollView, and it’s superview
5. rotating a device only calls layoutSubview on the parent view (the responding viewControllers primary view)
6. removeFromSuperview – layoutSubviews is called on superview only (not show in table)

翻译如下

1. init不会引起layoutSubviews的调用；
2. addSubview会引起父view以及该父view所有子view的layoutSubviews方法的调用；
3. setFrame会在frame发生变化的时候引起layoutSubview的调用；
4. 滚动一个UIScrollview会引起该UIScrollview以及其父view的layoutSubviews的调用；
5. 滚动设备会引起当前viewController的view的layoutSubviews调用；
6. removeFromSuperview会调用父view的layoutSubviews；

ARC 和 Non-ARC

In a non-ARC environment this Rules to remember

• You have ownership of any objects you create.
• You can take ownership of an object using retain.
• When no longer needed, you must relinquish ownership of an object you own.
• You must not relinquish ownership of an object you don’t own.

Take ownership of a object in this methods which name likes

• alloc
• new
• copy
• mutableCopy
• and “retain” also take the ownship

In ARC , follow below rules

• Forget about using retain, release, retainCount, and autorelease.
• Forget about using NSAllocateObject and NSDeallocateObject.
• Follow the naming rule for methods related to object creation.
• Forget about calling dealloc explicitly.
• Use @autoreleasepool instead of NSAutoreleasePool.
• Forget about using Zone (NSZone).
• Object type variables can’t be members of struct or union in C language.(__bridge __bridge_retain __bridge_transfer)
• ‘id’ and ‘void*’ have to be cast explicitly.

the property qualifier means

ARC & Non-ARC

In a non-ARC environment this Rules to remember

• You have ownership of any objects you create.
• You can take ownership of an object using retain.
• When no longer needed, you must relinquish ownership of an object you own.
• You must not relinquish ownership of an object you don’t own.

Take ownership of a object in this methods which name likes

• alloc
• new
• copy
• mutableCopy
• and “retain” also take the ownship

In ARC , follow below rules

• Forget about using retain, release, retainCount, and autorelease.
• Forget about using NSAllocateObject and NSDeallocateObject.
• Follow the naming rule for methods related to object creation.
• Forget about calling dealloc explicitly.
• Use @autoreleasepool instead of NSAutoreleasePool.
• Forget about using Zone (NSZone).
• Object type variables can’t be members of struct or union in C language.(__bridge __bridge_retain __bridge_transfer)
• ‘id’ and ‘void*’ have to be cast explicitly.

the property qualifier means