Android---MVC/MVP/MVVM的演进
目录
一个文件打天下
一个文件--->MVC
MVC--->MVP
MVP--->MVVM
6大设计原则
完整demo
我们通过"#字棋"游戏来展现MVC-->MVP-->MVVM 之间的演进
一个文件打天下
数据、视图以及逻辑都放在一个 class 里面。而一个 class 里最多 500 行代码，当代码过多时是很难维护的。页面是给用户看到，用户的需求是不断改变的，所以需要不定期的维护、迭代代码，所以一个 class 里面的代码要尽量少，不超过500行。
"#字棋"游戏的逻辑实现代码，全部放在了 MainActivity.java 里，如下：
package com.example.jingziqi;import static com.example.jingziqi.MainActivity.Player.O;
import static com.example.jingziqi.MainActivity.Player.X;import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;public class MainActivity extends AppCompatActivity {private static final String TAG = MainActivity.class.getName();// 定义一个棋手public enum Player {X, O}// 定义棋盘的格子，里面有个棋手public static class Cell{private Player value;public Player getValue(){return value;}public void setValue(Player value){this.value = value;}}// 总共定义 9 个格子private final Cell[][] cells = new Cell[3][3];private Player winner; // 记录结果，谁赢了private GameState state; //记录当前的游戏状态private Player currentTurn; // 现在是那位棋手在下---X/Oprivate enum GameState {IN_PROGRESS, FINISHED} //游戏的状态---进行/结束// Viewsprivate ViewGroup buttonGrid;private View winnerPlayerViewGroup;private TextView winnerPlayerLabel;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);winnerPlayerLabel = findViewById(R.id.winnerPlayerLabel);winnerPlayerViewGroup = findViewById(R.id.winnerPlayerViewGroup);buttonGrid = findViewById(R.id.buttonGrid);restart();}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {MenuInflater inflater = getMenuInflater();inflater.inflate(R.menu.menu_jingziqi, menu);return true;}@Overridepublic boolean onOptionsItemSelected(@NonNull MenuItem item) {switch (item.getItemId()) {case R.id.action_reset:restart();return true;default:return super.onOptionsItemSelected(item);}}public void onCellClicked(View view) {Button button = (Button) view;String tag = button.getTag().toString();// 取到点击的格子的行/列int row = Integer.parseInt(tag.substring(0, 1));int col = Integer.parseInt(tag.substring(1, 2));Log.i(TAG, "Click Row: [" + row + ", " + col + "]");Player playerThatMoved = mark(row, col);if (playerThatMoved != null) {button.setText(playerThatMoved.toString());if (getWinner() != null) {winnerPlayerLabel.setText(playerThatMoved.toString());winnerPlayerViewGroup.setVisibility(View.VISIBLE);}}}/* TODO 标记当前选手选择了哪行哪列* 如果不是在没有选中的9个格子里面点击，将视为无效* 另外，如果游戏已经结束，本次标记忽略* @param row [0, 2]* @param col [0, 2]* @return 返回当前选手，如果点击无效为 null*/public Player mark(int row, int col) {Player playerThatMoved = null;if(isValid(row, col)){ // 判断当前点击格子是否有效cells[row][col].setValue(currentTurn); // 标记该格子，当前棋手的符合(X/O)playerThatMoved = currentTurn; // 记录当前下棋的人是谁if(isWinningMoveByPlayer(currentTurn, row, col)){//TODO 判断当前这个棋手下棋后，该棋手是否获胜，即游戏是否需要结束state = GameState.FINISHED; //棋局的状态--结束winner = currentTurn; // 当前棋手获胜}else {// 切换到另外一棋手，继续flipCurrentTurn();}}return playerThatMoved;}public Player getWinner(){return winner;}// 清空棋盘private void clearCells(){for (int i = 0; i < 3; i++) {for (int j = 0; j < 3; j++) {cells[i][j] = new Cell();}}}// 判断当前点击是否有效private boolean isValid(int row, int col){if (state == GameState.FINISHED) { // 看棋子有没有结束return false;}else if (isCellValueAlreadySet(row, col)){ // 看该格子是否之前已经下过return false;}else {return true;}}private boolean isCellValueAlreadySet(int row, int col){return cells[row][col].getValue() != null;}/* TODO判断当前棋手下棋后---是否赢棋* @param player 棋手* @param currentRow 当前行* @param currentCol 当前列* @return TODO 如果当前行、当前列或者两条对角线为同一棋手，返回 true*/private boolean isWinningMoveByPlayer(Player player, int currentRow, int currentCol){return (cells[currentRow][0].getValue() ==player&& cells[currentRow][1].getValue() == player&& cells[currentRow][2].getValue() == player // 3-行|| cells[0][currentCol].getValue() == player&& cells[1][currentCol].getValue() == player&& cells[2][currentCol].getValue() == player // 3-列|| currentRow == currentCol&& cells[0][0].getValue() == player&& cells[1][1].getValue() == player&& cells[2][2].getValue() == player // 对角线|| currentRow + currentCol == 2&& cells[0][2].getValue() == player&& cells[1][1].getValue() == player&& cells[2][0].getValue() == player);}private void flipCurrentTurn() {currentTurn = currentTurn == X ? O :X;}/* TODO 开始一个新游戏，清除计分板和状态*/private void restart() {// 重置数据clearCells();winner = null;currentTurn = X;state = GameState.IN_PROGRESS;// 重置 ViewwinnerPlayerViewGroup.setVisibility(View.GONE);winnerPlayerLabel.setText("");for (int i = 0; i < buttonGrid.getChildCount(); i++) {((Button) buttonGrid.getChildAt(i)).setText("");}}
}
一个文件--->MVC
适用场景：适合设计类页面，就大多数都是数据，没有太多的控制逻辑。把数据剥离出去就ok
在 MVC 中我们将把写在一个 class 里的代码进行拆分
数据(Model): 数据+对数据进行的操作（不依赖视图的操作）
视图(View): 不同的模式有不同的定义：xml+activity+fragment = View 合集
逻辑(Controller): view 和 model 的通信和交互。
注意：在 MVC 中，activity 是属于 Controller，在 MVP/MVVM 中是属于 View。
如下图所示，我们把原来在 ManiActivity 中的数据+对数据的操作部分抽离到了 model 模块中，而 MainActivity 中留下了对 View 部分 + View 和 Model 的交互。
Model
在 MVC 中，我们把数据部分(Cell/Player/GameState/以及对数据的操作Board)抽离出来，放到 model 模块
1. Cell.java
package com.example.jingziqi_mvc.model;public class Cell {private Player value;public Player getValue() {return value;}public void setValue(Player value) {this.value = value;}
}
2. Player.java
package com.example.jingziqi_mvc.model;/* X/O代表两个棋手*/
public enum Player {X,O
}3. GamaState.java
package com.example.jingziqi_mvc.model;public enum GameState {IN_PROGRESS,FINISHED
}
4. Board.java
package com.example.jingziqi_mvc.model;import static com.example.jingziqi_mvc.model.Player.X;
import static com.example.jingziqi_mvc.model.Player.O;public class Board {// 总共定义 9 个格子private final Cell[][] cells = new Cell[3][3];private Player winner; // 记录结果，谁赢了private GameState state; //记录当前的游戏状态private Player currentTurn; // 现在是那位棋手在下---X/Opublic Board(){restart();}/* TODO 开始一个新游戏，清除计分板和状态*/public void restart() {clearCells();winner = null;currentTurn = X;state = GameState.IN_PROGRESS;}/* 清空棋盘上的X/O*/private void clearCells() {for (int i = 0; i < 3; i++) {for (int j = 0; j < 3; j++) {cells[i][j] = new Cell();}}}/* TODO 标记当前选手选择了哪行哪列* 如果不是在没有选中的9个格子里面点击，将视为无效* 另外，如果游戏已经结束，本次标记忽略* @param row [0, 2]* @param col [0, 2]* @return 返回当前选手，如果点击无效为 null*/public Player mark(int row, int col) {Player playerThatMoved = null;if(isValid(row, col)){ // 判断当前点击格子是否有效cells[row][col].setValue(currentTurn); // 标记该格子，当前棋手的符合(X/O)playerThatMoved = currentTurn; // 记录当前下棋的人是谁if(isWinningMoveByPlayer(currentTurn, row, col)){//TODO 判断当前这个棋手下棋后，该棋手是否获胜，即游戏是否需要结束state = GameState.FINISHED; //棋局的状态--结束winner = currentTurn; // 当前棋手获胜}else {// 切换到另外一棋手，继续flipCurrentTurn();}}return playerThatMoved;}public Player getWinner(){return winner;}/* 判断当前点击是否有效*/private boolean isValid(int row, int col){if (state == GameState.FINISHED) { // 看棋子有没有结束return false;}else if (isCellValueAlreadySet(row, col)){ // 看该格子是否之前已经下过return false;}else {return true;}}private boolean isCellValueAlreadySet(int row, int col){return cells[row][col].getValue() != null;}/* TODO判断当前棋手下棋后---是否赢棋* @param player 棋手* @param currentRow 当前行* @param currentCol 当前列* @return TODO 如果当前行、当前列或者两条对角线为同一棋手，返回 true*/private boolean isWinningMoveByPlayer(Player player, int currentRow, int currentCol){return (cells[currentRow][0].getValue() ==player&& cells[currentRow][1].getValue() == player&& cells[currentRow][2].getValue() == player // 3-行|| cells[0][currentCol].getValue() == player&& cells[1][currentCol].getValue() == player&& cells[2][currentCol].getValue() == player // 3-列|| currentRow == currentCol&& cells[0][0].getValue() == player&& cells[1][1].getValue() == player&& cells[2][2].getValue() == player // 对角线|| currentRow + currentCol == 2&& cells[0][2].getValue() == player&& cells[1][1].getValue() == player&& cells[2][0].getValue() == player);}/* 切换棋手*/private void flipCurrentTurn() {currentTurn = currentTurn == X ? O :X;}
}
Controler
在 mvc 中 View 只有 xml 的内容
MainActivity.java 的内容如下：
package com.example.jingziqi_mvc.controller;import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;import com.example.jingziqi_mvc.R;
import com.example.jingziqi_mvc.model.Board;
import com.example.jingziqi_mvc.model.Player;public class MainActivity extends AppCompatActivity {private static final String TAG = MainActivity.class.getName();private Board model;// View 部分private ViewGroup buttonGrid;private View winnerPlayerViewGroup;private TextView winnerPlayerLabel;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);winnerPlayerLabel = findViewById(R.id.winnerPlayerLabel);winnerPlayerViewGroup = findViewById(R.id.winnerPlayerViewGroup);buttonGrid = findViewById(R.id.buttonGrid);model = new Board();}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {MenuInflater inflater = getMenuInflater();inflater.inflate(R.menu.menu_jingziqi, menu);return true;}@Overridepublic boolean onOptionsItemSelected(@NonNull MenuItem item) {switch (item.getItemId()) {case R.id.action_reset:model.restart();//重置 Model(数据)restartView(); //重置Viewreturn true;default:return super.onOptionsItemSelected(item);}}/* 重置 View*/private void restartView() {winnerPlayerViewGroup.setVisibility(View.GONE);winnerPlayerLabel.setText("");for (int i = 0; i < buttonGrid.getChildCount(); i++) {((Button) buttonGrid.getChildAt(i)).setText("");}}/* 点击格子*/public void onCellClicked(View view) {Button button = (Button) view;String tag = button.getTag().toString();// 取到点击的格子的行/列int row = Integer.parseInt(tag.substring(0, 1));int col = Integer.parseInt(tag.substring(1, 2));Log.i(TAG, "Click Row: [" + row + ", " + col + "]");// TODO View 和 Model 的交互Player playerThatMoved = model.mark(row, col);if (playerThatMoved != null) {button.setText(playerThatMoved.toString());if (model.getWinner() != null) {winnerPlayerLabel.setText(playerThatMoved.toString());winnerPlayerViewGroup.setVisibility(View.VISIBLE);}}}
}MVC 对比 一个文件打天下
进步：抽离了 model，对数据进行单独封装
缺陷：controller(activity)权限太大，什么事情都能做（View 和 Model 的交互仍然保留在了 activity 中）。当我们的需求增加时，View 和 Model 的交互也会增加，此时activity 就会变得越来越大。
MVC--->MVP
数据(Model): 数据+对数据进行的操作（不依赖视图的操作）
视图(View): 不同的模式有不同的定义：xml+activity+fragment = View 合集
逻辑(Presenter)：实现view 和 model 之间的交互。让 activity 完全成为 view 模块
注意：增加了接口，在 Activity 中实现，然后再在 presenter 里调用
Model
1. Cell.java
package com.example.jingziqi_mvc.model;public class Cell {private Player value;public Player getValue() {return value;}public void setValue(Player value) {this.value = value;}
}
2. Player.java
package com.example.jingziqi_mvc.model;/* X/O代表两个棋手*/
public enum Player {X,O
}3. GamaState.java
package com.example.jingziqi_mvc.model;public enum GameState {IN_PROGRESS,FINISHED
}
4. Board.java
package com.example.jingziqi_mvp.model;import static com.example.jingziqi_mvp.model.Player.O;
import static com.example.jingziqi_mvp.model.Player.X;public class Board {// 总共定义 9 个格子private final Cell[][] cells = new Cell[3][3];private Player winner; // 记录结果，谁赢了private GameState state; //记录当前的游戏状态private Player currentTurn; // 现在是那位棋手在下---X/Opublic Board(){restart();}/* TODO 开始一个新游戏，清除计分板和状态*/public void restart() {clearCells();winner = null;currentTurn = X;state = GameState.IN_PROGRESS;}/* 清空棋盘上的X/O*/private void clearCells() {for (int i = 0; i < 3; i++) {for (int j = 0; j < 3; j++) {cells[i][j] = new Cell();}}}/* TODO 标记当前选手选择了哪行哪列* 如果不是在没有选中的9个格子里面点击，将视为无效* 另外，如果游戏已经结束，本次标记忽略* @param row [0, 2]* @param col [0, 2]* @return 返回当前选手，如果点击无效为 null*/public Player mark(int row, int col) {Player playerThatMoved = null;if(isValid(row, col)){ // 判断当前点击格子是否有效cells[row][col].setValue(currentTurn); // 标记该格子，当前棋手的符合(X/O)playerThatMoved = currentTurn; // 记录当前下棋的人是谁if(isWinningMoveByPlayer(currentTurn, row, col)){//TODO 判断当前这个棋手下棋后，该棋手是否获胜，即游戏是否需要结束state = GameState.FINISHED; //棋局的状态--结束winner = currentTurn; // 当前棋手获胜}else {// 切换到另外一棋手，继续flipCurrentTurn();}}return playerThatMoved;}public Player getWinner(){return winner;}/* 判断当前点击是否有效*/private boolean isValid(int row, int col){if (state == GameState.FINISHED) { // 看棋子有没有结束return false;}else if (isCellValueAlreadySet(row, col)){ // 看该格子是否之前已经下过return false;}else {return true;}}private boolean isCellValueAlreadySet(int row, int col){return cells[row][col].getValue() != null;}/* TODO判断当前棋手下棋后---是否赢棋* @param player 棋手* @param currentRow 当前行* @param currentCol 当前列* @return TODO 如果当前行、当前列或者两条对角线为同一棋手，返回 true*/private boolean isWinningMoveByPlayer(Player player, int currentRow, int currentCol){return (cells[currentRow][0].getValue() ==player&& cells[currentRow][1].getValue() == player&& cells[currentRow][2].getValue() == player // 3-行|| cells[0][currentCol].getValue() == player&& cells[1][currentCol].getValue() == player&& cells[2][currentCol].getValue() == player // 3-列|| currentRow == currentCol&& cells[0][0].getValue() == player&& cells[1][1].getValue() == player&& cells[2][2].getValue() == player // 对角线|| currentRow + currentCol == 2&& cells[0][2].getValue() == player&& cells[1][1].getValue() == player&& cells[2][0].getValue() == player);}/* 切换棋手*/private void flipCurrentTurn() {currentTurn = currentTurn == X ? O :X;}
}
View
1. MainActivity.java
package com.example.jingziqi_mvp.view;import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;import com.example.jingziqi_mvp.R;
import com.example.jingziqi_mvp.presenter.JingziqiPresenter;public class MainActivity extends AppCompatActivity implements JingziqiView{private static final String TAG = MainActivity.class.getName();JingziqiPresenter presenter = new JingziqiPresenter(this);// View 部分private ViewGroup buttonGrid;private View winnerPlayerViewGroup;private TextView winnerPlayerLabel;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);winnerPlayerLabel = (TextView) findViewById(R.id.winnerPlayerLabel);winnerPlayerViewGroup = findViewById(R.id.winnerPlayerViewGroup);buttonGrid = (ViewGroup) findViewById(R.id.buttonGrid);}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {MenuInflater inflater = getMenuInflater();inflater.inflate(R.menu.menu_jingziqi, menu);return true;}@Overridepublic boolean onOptionsItemSelected(@NonNull MenuItem item) {switch (item.getItemId()) {case R.id.action_reset:presenter.onResetSelected();return true;default:return super.onOptionsItemSelected(item);}}public void onCellClicked(View view) {Button button = (Button) view;String tag = button.getTag().toString();// 取到点击的格子的行/列int row = Integer.parseInt(tag.substring(0, 1));int col = Integer.parseInt(tag.substring(1, 2));Log.i(TAG, "Click Row: [" + row + ", " + col + "]");// TODO View 和 Model 的交互抽离到 presenter 里了presenter.onButtonSelected(row, col);}/* 展示获胜者*/@Overridepublic void showWinner(String winningPlayerDisplayLabel) {winnerPlayerLabel.setText(winningPlayerDisplayLabel);winnerPlayerViewGroup.setVisibility(View.VISIBLE);}/* 把格子下面，展示谁获胜的内容清空*/@Overridepublic void clearWinnerDisplay() {winnerPlayerViewGroup.setVisibility(View.GONE);winnerPlayerLabel.setText("");}/* 把格子清空*/@Overridepublic void clearButton() {for( int i = 0; i < buttonGrid.getChildCount(); i++ ) {((Button) buttonGrid.getChildAt(i)).setText("");}}/* 在格子上标记是那位棋手下的棋(即在格子上标记X/O)*/@Overridepublic void setButtonText(int row, int col, String text) {Button btn = (Button) buttonGrid.findViewWithTag("" + row + col); // 根据 tag 找到对应的 格子if(btn != null) {btn.setText(text);}}
}2. JingziqiView.java 是一个接口，在 MainActivity 里实现，在 Presenter 里完成调用
package com.example.jingziqi_mvp.view;public interface JingziqiView {void showWinner(String winningPlayerDisplayLabel);void clearWinnerDisplay();void clearButton();void setButtonText(int row, int col, String text);
}
Presenter
1. JingziqiPresenter.java
package com.example.jingziqi_mvp.presenter;import android.view.View;import com.example.jingziqi_mvp.model.Board;
import com.example.jingziqi_mvp.model.Player;
import com.example.jingziqi_mvp.view.JingziqiView;public class JingziqiPresenter {private JingziqiView view;private Board model;public JingziqiPresenter(JingziqiView view){this.view = view;this.model = new Board();}public void onButtonSelected(int row, int col){// TODO View 和 Model 的交互Player playerThatMoved = model.mark(row, col);if (playerThatMoved != null) {//button.setText(playerThatMoved.toString());view.setButtonText(row, col, playerThatMoved.toString());if (model.getWinner() != null) {
// winnerPlayerLabel.setText(playerThatMoved.toString());
// winnerPlayerViewGroup.setVisibility(View.VISIBLE);view.showWinner(playerThatMoved.toString());}}}public void onResetSelected(){model.restart();view.clearWinnerDisplay();view.clearButton();}
}
MVP 相对 MVC
进步：activity 只剩下了 view，presenter 承担了 view 和 model 之间的交互，满足单一职责原则，视图数据逻辑是清晰的。
缺陷：引入了 interface，方法增多，增加一个方法要改多个地方。
MVP--->MVVM
数据(Model): 数据+对数据进行的操作（不依赖视图的操作）
视图(View): 不同的模式有不同的定义：xml+activity+fragment = View 合集
VM(viewmodel)：将视图与数据进行绑定，使用 dataBinding 完成
viewBinding: 只能省略 findViewById, 不需要修改 xml
dataBinding: 除了 ViewBinding 的功能还能绑定 data，需要修改 xml
Model
model 模块仍然不变，与 MVC/MVP 的 Model 内容一致
View
MainActivity.java
package com.example.jingziqi_mvvm.view;import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;import com.example.jingziqi_mvvm.R;
import com.example.jingziqi_mvvm.databinding.ActivityMainBinding;
import com.example.jingziqi_mvvm.viewmodel.JingziqiViewModel;public class MainActivity extends AppCompatActivity {JingziqiViewModel viewModel = new JingziqiViewModel();@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);// TODO dataBinding 的使用ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);binding.setViewModel(viewModel);}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {MenuInflater inflater = getMenuInflater();inflater.inflate(R.menu.menu_jingziqi, menu);return true;}@Overridepublic boolean onOptionsItemSelected(@NonNull MenuItem item) {switch (item.getItemId()) {case R.id.action_reset:viewModel.onResetSelect();return true;default:return super.onOptionsItemSelected(item);}}
}ViewModel
package com.example.jingziqi_mvvm.viewmodel;import androidx.databinding.ObservableArrayMap;
import androidx.databinding.ObservableField;import com.example.jingziqi_mvvm.model.Board;
import com.example.jingziqi_mvvm.model.Player;public class JingziqiViewModel {private Board model;public final ObservableArrayMap<String, String> cells = new ObservableArrayMap<>();public final ObservableField<String> winner = new ObservableField<>();public JingziqiViewModel(){model = new Board();}public void onResetSelect(){model.restart();winner.set(null);cells.clear();}public void onClickedCellAt(int row, int col){Player playerThatMoved = model.mark(row, col);if (playerThatMoved != null) {cells.put("" + row + col, playerThatMoved.toString());winner.set(model.getWinner() == null ? null : model.getWinner().toString());}}
}
MVVM 使用 dataBinding 将数据绑定在 View 上。所以我们要引入 dataBinding。在 app 级的 build.gradle 里添加
使用 dataBinding，我们还得修改 xml ，将整个布局包裹住 <layout>....</layout > 中，并且引入数据部分。注意，<data></data> 里的 type 所指示的内容，就是我们 VM 模块的 JingziqiViewModel.java 。并且在该 xml 里会用到 JingziqiViewModel的方法。
使用 JingziqiViewModel 里的 onClickedCellAt()方法，以及 cells 成员变量。
通过上述内容，我们把对格子内容的改变(数据)直接绑定在 view 上，这样代码就更简介了。
6大设计原则
单一职责原则、开闭原则、里氏替换原则、接口隔离原则、依赖倒置原则、迪米特原则
单一职责原则：一个 class 完成一件事情。
开闭原则：对扩展、继承开发，对修改关闭。
里氏替换原则：不能改变基类的逻辑(比如，继承父类的run() 方法，哪里里面的实现逻辑就不能是 fly)
依赖倒置原则：两个模块之间通信，通过接口实现（不依赖实现，只依赖接口）
完整demo
下面给出上面 4 种写法的完整代码。可以查看具体的 xml ，以及更多的代码细节。
链接：https://pan.baidu.com/s/1qxJQ-6iIDgm7AX-6CmGuuQ
提取码：2b77
