在Android中用于保存Activity状态的onSaveInstanceState()和恢复Activity状态的onRestoreInstanceState(),
这种算不算是一种备忘录模式呢?
1、定义:
在不破坏封装的情况下,捕获对象的内部状态,并在对象之外保存这个状态,这样以后就可以恢复以后保存的状态;
2、使用:
备忘录模式,比较适合用于功能复杂,但是需要维护和纪录历史的类,或者是需要保存一个或者是多个属性的类,
在未来某个时段需要时,将其还原到原来纪录的状态;
Originator可以根据保存的Memento还原到前一状态;
3、其他:
备忘录模式又称之为:快照模式(Snapshot Pattern)或Token模式,是对象的行为模式;
4、简单的demo:
首先是需要处理的对象数据:
package com.example.demo.Memento; /** * 对象 * @author qubian * @data 2015年6月20日 * @email [email protected] * */ public class Bean { private String name; private String age; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getAge() { return age; } public void setAge(String age) { this.age = age; } public Memento createMemento(String name,String age) { return new Memento(name, age); } public void restore(Memento memento) { this.name=memento.getName(); this.age= memento.getAge(); } }
备忘数据对象:
1、这个可以存储和被处理的对象一样的数据,也可以根据需要修改,设置自己的数据;
2、需要明确的功能仅仅是为了存储和恢复被处理的对象,故其中的数据可以随意约定,
3、那么,问题来了,这个备份的数据,一般都是存储在内存中,用于恢复对象,那么如果将被处理的对象,序列化,或者是运用反射等技术用于存储和恢复,那么这样存储在磁盘中,这样是否有意义,或者是违背了这样的设计模式呢?
4、也就是原来的问题,在Android中onSaveInstanceState中的数据,一般都是使用的Android的存储方式,是为了在Activity在内存中销毁后的恢复问题,那么备忘录模式中存储在内存的对象,在此时,似乎就没有什么意义了!?
package com.example.demo.Memento; /** * 备忘录 备忘数据 * @author qubian * @data 2015年6月20日 * @email [email protected] * */ public class Memento { private String name; private String age; public Memento(String name,String age) { this.name=name; this.age= age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getAge() { return age; } public void setAge(String age) { this.age = age; } }
备忘录管理者以及使用者:
package com.example.demo.Memento; /** * 备忘录模式 * 管理者 * @author qubian * @data 2015年6月20日 * @email [email protected] * */ public class MementoManager { private Memento memento; public Memento getMemento() { return memento; } public void setMemento(Memento memento) { this.memento = memento; } } package com.example.demo.Memento; public class UseMemento { public void use() { Bean bean =new Bean(); bean.setName("张三"); bean.setAge("22"); // 保存状态 MementoManager manager = new MementoManager(); manager.setMemento(bean.createMemento(bean.getName(), bean.getAge())); // 改变状态 bean.setAge("23"); //恢复原来地状态 bean.restore(manager.getMemento()); } }
在管理者其中,备忘数据对象Memento,可以放在管理者中统一管理;
在管理者中,也可以存在多种状态的Memento,上例子中,仅仅存放了一个简单的状态;
5、在备忘录模式的定义中,是说,在此对象之外保存这个对象的状态,那么,如果这么说来,存在内存和磁盘中,然后处理后返回原来的对象数据,这样似乎也都是一种备忘录模式咯?!
6、Android:
1、那么如果这么说来,Activity 本身就用到了这样的设计模式了,
2、在横竖屏切换的时候,线程Thread会重新启动,这个问题是横竖屏切换的时候需要处理的,那么,我们在此需要也是需要考虑的这么模式,就是线程重启的时候,线程中的数据,我们也是肯定需要用到这个模式的,用来保存原来的数据;
3、在JNI 调用本地数据中的Canvas中的Save() 和Restore()这两个本地JNI 代码中是否也运用这样的设计模式呢?!
public class Canvas { /** * Saves the current matrix and clip onto a private stack. Subsequent * calls to translate,scale,rotate,skew,concat or clipRect,clipPath * will all operate as usual, but when the balancing call to restore() * is made, those calls will be forgotten, and the settings that existed * before the save() will be reinstated. * * @return The value to pass to restoreToCount() to balance this save() */ public native int save(); /** * Based on saveFlags, can save the current matrix and clip onto a private * stack. Subsequent calls to translate,scale,rotate,skew,concat or * clipRect,clipPath will all operate as usual, but when the balancing * call to restore() is made, those calls will be forgotten, and the * settings that existed before the save() will be reinstated. * * @param saveFlags flag bits that specify which parts of the Canvas state * to save/restore * @return The value to pass to restoreToCount() to balance this save() */ public native int save(int saveFlags); /** * This behaves the same as save(), but in addition it allocates an * offscreen bitmap. All drawing calls are directed there, and only when * the balancing call to restore() is made is that offscreen transfered to * the canvas (or the previous layer). Subsequent calls to translate, * scale, rotate, skew, concat or clipRect, clipPath all operate on this * copy. When the balancing call to restore() is made, this copy is * deleted and the previous matrix/clip state is restored. * * @param bounds May be null. The maximum size the offscreen bitmap * needs to be (in local coordinates) * @param paint This is copied, and is applied to the offscreen when * restore() is called. * @param saveFlags see _SAVE_FLAG constants * @return value to pass to restoreToCount() to balance this save() */ public int saveLayer(RectF bounds, Paint paint, int saveFlags) { return native_saveLayer(mNativeCanvas, bounds, paint != null ? paint.mNativePaint : 0, saveFlags); } /** * This call balances a previous call to save(), and is used to remove all * modifications to the matrix/clip state since the last save call. It is * an error to call restore() more times than save() was called. */ public native void restore(); }