Android的MVC

前言

大家都知道Android的设计架构是基于MVC的。对于MVC大家并没有”陌生”，而且一般来说，这个是一个广泛使用的框架。用游戏来讲述MVC是最好的，因为对于Control层的理解比较直观：control就是游戏的控制，上下左右，技能ABC，游戏的时间，事件；View是对绘制UI，场景的Face，人物Body（不知道Model是什么）；Model是实体,具有动作。

MVC模型

大致的流向，用户的输入改变Model，并且改变View，View显示动作的Action给Control，Model的改变Notify控制。

重要的是：

• 模型和视图要严格的分离（不能有交互）

贪吃蛇游戏的简易mvc代码

在结构上安装model，view，control来分类，代码整体的包结构如下：

编写View

注意的是view是独立的模块，不能关联control和mode,l那么就有了以下代码。说明，view是游戏的UI，它只关心绘制的点，和场景，不关心蛇，游戏。所以，我们可以独立这个view来测试，譬如测试绘制蛇，绘制食物；

package com.owant.mvcsnakegame.view;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

import com.owant.mvcsnakegame.model.Location;

import java.util.ArrayList;

/**
 * Created by owant on 16/11/2016.
 */
public class SnakeGameView extends View {

    public static final int screenX = 30;
    public static final int screenY = 30;

    private int dx;
    private int dy;
    public ArrayList<Location> body;
    public Location food;

    private Paint mPaint;

    public SnakeGameView(Context context) {
        this(context, null, 0);
    }

    public SnakeGameView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public SnakeGameView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        mPaint = new Paint();
        mPaint.setColor(Color.RED);
        mPaint.setAntiAlias(true);
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setStrokeWidth(2);

//        testDrawSnakeBody();

//        testFood();

    }

    private void testFood() {
        food = new Location();
        food.rawY = 3;
        food.rawX = 5;
    }

    private void testDrawSnakeBody() {
        body = new ArrayList<>();
        Location location = new Location();
        location.rawX = 0;
        location.rawY = 0;
        body.add(location);

        Location location1 = new Location();
        location1.rawX = 0;
        location1.rawY = 1;
        body.add(location1);

        Location location2 = new Location();
        location2.rawX = 0;
        location2.rawY = 2;
        body.add(location2);

        Location location3 = new Location();
        location3.rawX = 0;
        location3.rawY = 3;
        body.add(location3);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        drawScreen(canvas);


        drawSnake(canvas);

        drawFood(canvas);

    }

    /**
     * draw the game screen
     *
     * @param canvas
     */
    private void drawScreen(Canvas canvas) {
        mPaint.setColor(Color.RED);

        //x
        for (int i = 1; i < screenX; i++) {
            canvas.drawLine(dx * i, 0, dx * i, getHeight(), mPaint);
        }

        //y
        for (int i = 1; i < screenY; i++) {
            canvas.drawLine(0, dy * i, getWidth(), dy * i, mPaint);
        }
    }

    /**
     * draw the snake body
     *
     * @param canvas
     */
    private void drawSnake(Canvas canvas) {
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setColor(Color.RED);
        if (body != null) {
            for (Location b : body) {
                canvas.drawRect(b.rawX * dx, b.rawY * dy, b.rawX * dx + dx, b.rawY * dy + dy, mPaint);
            }
        }
    }

    /**
     * draw the food
     *
     * @param canvas
     */
    private void drawFood(Canvas canvas) {
        if (food != null) {
            mPaint.setColor(Color.GREEN);
            canvas.drawRect(food.rawX*dx, food.rawY*dx, food.rawX*dx + dx, food.rawY*dx + dy, mPaint);
        }
    }


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        dx = getWidth() / screenX;
        dy = getHeight() / screenY;
    }

    public ArrayList<Location> getBody() {
        return body;
    }

    public void setBody(ArrayList<Location> bodys) {
        this.body = bodys;
    }

    @Override
    public void invalidate() {
        super.invalidate();
    }

    public Location getFood() {
        return food;
    }

    public void setFood(Location food) {
        this.food = food;
    }

    public void clearFood() {
        this.food = null;
    }

}

Model的编写

Snake。说明，蛇对自己的特性负责，不理会control和view；

package com.owant.mvcsnakegame.model;

import java.util.ArrayList;

/**
 * Created by owant on 16/11/2016.
 */
public class Snake {

    public boolean live = true;

    public ArrayList<Location> body;
    public int direction = Direction.down;
    //30ms
    public int speek = 300;

    public Snake() {
        body = new ArrayList<>();
        init();
    }

    private void init() {
        Location location = new Location();
        location.rawX = 0;
        location.rawY = 0;
        body.add(location);

        Location location1 = new Location();
        location1.rawX = 0;
        location1.rawY = 1;
        body.add(location1);

        Location location2 = new Location();
        location2.rawX = 0;
        location2.rawY = 2;
        body.add(location2);

        Location location3 = new Location();
        location3.rawX = 0;
        location3.rawY = 3;
    }

    public int getDirection() {
        return direction;
    }

    public void setDirection(int direction) {
        this.direction = direction;
    }

    public void growUp() {
    }

    public Location getHeard() {
        return body.get(body.size() - 1);
    }

    public void move() {

        Location heard = getHeard();
        Location next = new Location();

        if (direction == Direction.up) {//向上
            next.rawX = heard.rawX;
            next.rawY = heard.rawY - 1;
        } else if (direction == Direction.down) {//向下
            next.rawX = heard.rawX;
            next.rawY = heard.rawY + 1;
        } else if (direction == Direction.left) {//左边
            next.rawX = heard.rawX - 1;
            next.rawY = heard.rawY;
        } else if (direction == Direction.right) {//右
            next.rawX = heard.rawX + 1;
            next.rawY = heard.rawY;
        }

        body.remove(0);
        body.add(next);
    }


}

Location 坐标点，代码省略。

Control

控制层，需要管理View和Model，它应该包括游戏的时间控制，游戏的输入。代码如下：

package com.owant.mvcsnakegame.control;

import com.owant.mvcsnakegame.model.Direction;
import com.owant.mvcsnakegame.model.Snake;
import com.owant.mvcsnakegame.view.SnakeGameView;

/**
 * Created by owant on 16/11/2016.
 */
public class GameControl implements Runnable {

    //control view
    SnakeGameView view;
    Snake snake;

    public GameControl(SnakeGameView view, Snake snake) {
        this.view = view;
        this.snake = snake;
    }

    public void right() {
        if (snake.getDirection() == Direction.down) {
            snake.setDirection(Direction.left);
        } else if (snake.getDirection() == Direction.up) {
            snake.setDirection(Direction.right);
        } else if (snake.getDirection() == Direction.left) {
            snake.setDirection(Direction.up);
        } else if (snake.getDirection() == Direction.right) {
            snake.setDirection(Direction.down);
        }
    }

    public void left() {
        if (snake.getDirection() == Direction.left) {
            snake.setDirection(Direction.down);
        } else if (snake.getDirection() == Direction.right) {
            snake.setDirection(Direction.up);
        } else if (snake.getDirection() == Direction.up) {
            snake.setDirection(Direction.left);
        } else if (snake.getDirection() == Direction.down) {
            snake.setDirection(Direction.right);
        }
    }

    @Override
    public void run() {
        do {
            try {
                Thread.sleep(snake.speek);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            snake.move();

            view.post(new Runnable() {
                @Override
                public void run() {
                    view.invalidate();
                }
            });
        } while (snake.live);
    }
}

Activity

至于为何有Activity内，因为Android的MVC设计，Control落在了Activity上，也可以独立为一层特殊的Control，因为GameControl已经实现了所有的控制功能。Activity只是程序的入口，初始化实体，视图，接受输入传递给GameControl就行。

package com.owant.mvcsnakegame;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.KeyEvent;

import com.owant.mvcsnakegame.control.GameControl;
import com.owant.mvcsnakegame.model.Snake;
import com.owant.mvcsnakegame.view.SnakeGameView;

public class MainActivity extends AppCompatActivity {


    GameControl control;
    Snake snake;
    SnakeGameView snakeGameView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        snake = new Snake();

        snakeGameView = (SnakeGameView) findViewById(R.id.main_snake_view);
        snakeGameView.setBody(snake.body);

        control = new GameControl(snakeGameView, snake);
        new Thread(control).start();

    }


    @Override
    protected void onResume() {
        super.onResume();
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        System.out.println(keyCode);
        if (keyCode == KeyEvent.KEYCODE_A) {
            control.left();
        } else if (keyCode == KeyEvent.KEYCODE_D) {
            control.right();
        }
        return super.onKeyDown(keyCode, event);
    }

}

大致对于MVC的框架有了一定了解了吧。

总结

mvc是一种框架，不是设计模式。框架是很灵活的，可以变动，主要是对model，view，control的分类，而且如何关联到Android的代码中去。注意的是：

• model和view是独立分开的。不要在view里面进行model和control的操作。

• 大多数的APP的control大多是loadData

一些错误和有异议的问题

• 我在网上看了一些人的mvc，发现他们的view层居然出现model和control，这是很错误的。譬如：
  

  • 在ListView的Adapter中写点击事件。
  • View出现Control和刷新，这个不能说错误，由于View自己刷新是Android自身提供的，而且代码写起来简易，可以考虑View自己刷新。