1、定义：
The Strategy Pattern defines a family of algorithms,encapsulates each one,and makes them interchangeable. Strategy lets the algorithm vary independently from
clients that use it.
定义了一系列的算法（这些算法实现了同样的工作。仅仅是实现不同），它能够已同样的方式调用全部的算法。降低算法类与算法之间的耦合。
2、目的：
将详细的算法抽象出来，把每一个算法独立出来，形成一系列的算法组，这个算法组里面的算法能够依据实际情况进行相互替换。
3、中心：
策略模式的中心，不在于怎样实现算法，而在于怎样组织和调用这些算法，即：解耦合。形成独立模块。增强程序拓展性。
写了一个简单的策略使用
首先，编写一个统一的算法接口
/**
* 策略模式
* 统一的算法接口
* @author qubian
* @data 2015年6月3日
* @email naibbian@163.com
*
*/
public interface StrategyPattern {
/**
* 计算注数
*/
public int calcLottery(int num);
}
其次，编写每一个详细的实现
package com.example.demo;
/**
* 策略模式
* 详细的方法实现；
* 比方说双色球
* @author qubian
* @data 2015年6月3日
* @email naibbian@163.com
*
*/
public class StrategyPatternImp_SSQ implements StrategyPattern {
@Override
public int calcLottery(int num) {
return 0;
}
}
package com.example.demo;
/**
* 策略模式
* 详细的方法实现；
* 比方说大乐透
* @author qubian
* @data 2015年6月3日
* @email naibbian@163.com
*
*/
public class StrategyPatternImp_DLT implements StrategyPattern{
@Override
public int calcLottery(int num) {
return 0;
}
}
最后是策略的不同调用
package com.example.demo;
/**
* 详细的使用
* @author qubian
* @data 2015年6月3日
* @email naibbian@163.com
*
*/
public class LotteryCount {
private StrategyPattern strategyPattern;
public enum LotteryEnum {
SSQ, DLT, QLC;
}
public int getLotteryCount(LotteryEnum e,int num)
{
switch (e) {
case SSQ:
strategyPattern = new StrategyPatternImp_SSQ();
break;
case DLT:
strategyPattern = new StrategyPatternImp_DLT();
break;
default:
break;
}
return strategyPattern.calcLottery(num);
}
}
策略模式 在Android Framework 中运用广泛。
比方说，我们常常使用的 BaseAdapter 实际也是策略模式；
我们编写的适配器继承自BaseAdapter，通过getview中实现不同的算法。实现不同的view的返回，
外部使用时也能够依据数据源。切换Adapter，这种使用事实上就是一种策略模式；
Adapter 就是一个最顶层的策略接口
public interface Adapter {
/**
* How many items are in the data set represented by this Adapter.
*
* @return Count of items.
*/
int getCount();
/**
* Get the data item associated with the specified position in the data set.
*
* @param position Position of the item whose data we want within the adapter's
* data set.
* @return The data at the specified position.
*/
Object getItem(int position);
/**
* Get a View that displays the data at the specified position in the data set. You can either
* create a View manually or inflate it from an XML layout file. When the View is inflated, the
* parent View (GridView, ListView...) will apply default layout parameters unless you use
* {@link android.view.LayoutInflater#inflate(int, android.view.ViewGroup, boolean)}
* to specify a root view and to prevent attachment to the root.
*
* @param position The position of the item within the adapter's data set of the item whose view
* we want.
* @param convertView The old view to reuse, if possible. Note: You should check that this view
* is non-null and of an appropriate type before using. If it is not possible to convert
* this view to display the correct data, this method can create a new view.
* Heterogeneous lists can specify their number of view types, so that this View is
* always of the right type (see {@link #getViewTypeCount()} and
* {@link #getItemViewType(int)}).
* @param parent The parent that this view will eventually be attached to
* @return A View corresponding to the data at the specified position.
*/
View getView(int position, View convertView, ViewGroup parent);
static final int IGNORE_ITEM_VIEW_TYPE = AdapterView.ITEM_VIEW_TYPE_IGNORE;
int getItemViewType(int position);
int getViewTypeCount();
static final int NO_SELECTION = Integer.MIN_VALUE;
boolean isEmpty();
}
再到BaseAdapter的抽象
public abstract class BaseAdapter implements ListAdapter, SpinnerAdapter {
private final DataSetObservable mDataSetObservable = new DataSetObservable();
public boolean hasStableIds() {
return false;
}
/**
* Notifies the attached observers that the underlying data has been changed
* and any View reflecting the data set should refresh itself.
*/
public void notifyDataSetChanged() {
mDataSetObservable.notifyChanged();
}
public View getDropDownView(int position, View convertView, ViewGroup parent) {
return getView(position, convertView, parent);
}
public int getItemViewType(int position) {
return 0;
}
public int getViewTypeCount() {
return 1;
}
public boolean isEmpty() {
return getCount() == 0;
}
}