设计模式之命令模式

定义

将一个请求封装成一个对象，从而让用户使用不同的请求把客户端参数化；对请求排队或者记录请求日志，以及支持可撤销的操作。

Android中源码使用命令模式

PackageHandler

特点

• 优点
  命令模式的封装性很好，更弱的耦合性，更灵活的控制性以及更好的扩展性。

• 2.缺点
  类的膨胀，大量衍生类的创建。

使用场景

（1）需要抽出待执行的动作，然后以参数的形式提供出来。

（2）在不同的时刻指定、排列和执行请求。一个命令对象可以有与初始请求无关的生存期。

（3）需要支持操作取消。

（4）支持修改日志功能，这样当系统崩溃时，这些修改可以被重做一遍。

（5）需要支持事务操作。

简单实现

需求：推箱子游戏。

/**
 * Created on 2019/4/4 11:33
 * 推箱子游戏类
 * @author Scarf Gong
 */
public class PushBox {
    public void toLeft() {
        Log.d("TAG", "Left");
    }

    public void toRight() {
        Log.d("TAG", "Right");
    }

    public void toUp() {
        Log.d("TAG", "Up");
    }

    public void toDown() {
        Log.d("TAG", "Down");
    }

    public void revoke() {
        Log.d("TAG", "撤销");
    }
}

/**
 * Created on 2019/4/4 11:36
 * 命令接口
 * @author Scarf Gong
 */
public interface Command {
    void execute();

    void getCommand();
}

--------------------------
/**
 * Created on 2019/4/4 11:37
 * 向下命令
 * @author Scarf Gong
 */
public class DownCommand implements Command {
    private PushBox mPushBox;

    public DownCommand(PushBox pushBox) {
        mPushBox = pushBox;
    }

    @Override
    public void execute() {
        mPushBox.toDown();
    }

    @Override
    public void getCommand() {
        Log.d("TAG", "⬇️️");
    }
}

--------------------------
/**
 * Created on 2019/4/4 11:37
 * 向左命令
 * @author Scarf Gong
 */
public class LeftCommand implements Command {
    private PushBox mPushBox;

    public LeftCommand(PushBox pushBox) {
        mPushBox = pushBox;
    }

    @Override
    public void execute() {
        mPushBox.toLeft();
    }

    @Override
    public void getCommand() {
        Log.d("TAG", "⬅️");
    }
}

--------------------------
/**
 * Created on 2019/4/4 11:37
 * 向右命令
 * @author Scarf Gong
 */
public class RightCommand implements Command {
    private PushBox mPushBox;

    public RightCommand(PushBox pushBox) {
        mPushBox = pushBox;
    }

    @Override
    public void execute() {
        mPushBox.toRight();
    }

    @Override
    public void getCommand() {
        Log.d("TAG", "➡️️");
    }
}


--------------------------
/**
 * Created on 2019/4/4 11:37
 * 向上命令
 * @author Scarf Gong
 */
public class UpCommand implements Command {
    private PushBox mPushBox;

    public UpCommand(PushBox pushBox) {
        mPushBox = pushBox;
    }

    @Override
    public void execute() {
        mPushBox.toUp();
    }

    @Override
    public void getCommand() {
        Log.d("TAG", "⬆️");
    }
}

--------------------------
/**
 * Created on 2019/4/4 11:37
 * 撤销命令
 * @author Scarf Gong
 */
public class RevokeCommand implements Command {
    private PushBox mPushBox;

    public RevokeCommand(PushBox pushBox) {
        mPushBox = pushBox;
    }

    @Override
    public void execute() {
        mPushBox.revoke();
    }

    @Override
    public void getCommand() {
        Log.d("TAG", "取消️");
    }
}

--------------------------

/**
 * Created on 2019/4/4 11:49
 * 请求者类
 * @author Scarf Gong
 */
public class Buttons {
    private LeftCommand mLeftCommand;
    private RightCommand mRightCommand;
    private UpCommand mUpCommand;
    private DownCommand mDownCommand;
    private RevokeCommand mRevokeCommand;

    private List<Command> mList = new ArrayList<>();

    public void getCommandList() {
        for (Command c:mList) {
            c.getCommand();
        }
    }

    public void setLeftCommand(LeftCommand leftCommand) {
        mLeftCommand = leftCommand;
    }

    public void setRightCommand(RightCommand rightCommand) {
        mRightCommand = rightCommand;
    }

    public void setUpCommand(UpCommand upCommand) {
        mUpCommand = upCommand;
    }

    public void setDownCommand(DownCommand downCommand) {
        mDownCommand = downCommand;
    }

    public void setRevokeCommand(RevokeCommand revokeCommand) {
        mRevokeCommand = revokeCommand;
    }

    public void toLeft() {
        mLeftCommand.execute();
        mList.add(mLeftCommand);
    }

    public void toRight() {
        mRightCommand.execute();
        mList.add(mRightCommand);
    }

    public void toUp() {
        mUpCommand.execute();
        mList.add(mUpCommand);
    }

    public void toDown() {
        mDownCommand.execute();
        mList.add(mDownCommand);
    }

    public void toRevoke() {
        mRevokeCommand.execute();
        mList.add(mRevokeCommand);
    }
}

使用：

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initData();
    }

    private void initData() {
        PushBox pushBox = new PushBox();

        LeftCommand leftCommand = new LeftCommand(pushBox);
        RightCommand rightCommand = new RightCommand(pushBox);
        UpCommand upCommand = new UpCommand(pushBox);
        DownCommand downCommand = new DownCommand(pushBox);
        RevokeCommand revokeCommand = new RevokeCommand(pushBox);

        Buttons buttons = new Buttons();
        buttons.setLeftCommand(leftCommand);
        buttons.setUpCommand(upCommand);
        buttons.setRightCommand(rightCommand);
        buttons.setDownCommand(downCommand);


        buttons.toDown();
        buttons.toLeft();
        buttons.toRight();
        buttons.toUp();
        buttons.getCommandList();
    }
}

输出结果：

2019-04-04 13:45:43 D/TAG: Down
2019-04-04 13:45:43 D/TAG: Left
2019-04-04 13:45:43 D/TAG: Right
2019-04-04 13:45:43 D/TAG: Up
2019-04-04 13:45:43 D/TAG: ⬇️️
2019-04-04 13:45:43 D/TAG: ⬅️
2019-04-04 13:45:43 D/TAG: ➡️️
2019-04-04 13:45:43 D/TAG: ⬆️