Android MVP架构

痛定思痛。 2022-11-12 12:56 191阅读 0赞

### 一、架构概述 ###

对于`MVP (Model View Presenter)`架构是从著名的`MVC(Model View Controller)`架构演变而来的。而对于`Android`应用的开发中本身可视为一种`MVC`架构。通常在开发中将`XML`文件视为`MVC`中的`View`角色，而将`Activity`则视为`MVC`中的`Controller`角色。不过更多情况下在实际应用开发中`Activity`不能够完全充当`Controller`，而是`Controller`和`View`的合体。于是`Activity`既要负责视图的显示，又要负责对业务逻辑的处理。这样在`Activity`中代码达到上千行，甚至几千行都不足为其，同时这样的`Activity`也显得臃肿不堪。所以对于`MVC`架构并不很合适运用于`Android`的开发中。

### 二、架构简介 ###

对于一个应用而言我们需要对它抽象出各个层面，而在`MVP`架构中它将`UI`界面和数据进行隔离，所以我们的应用也就分为三个层次。

1.  `View`:对于`View`层也是视图层，在`View`层中只负责对数据的展示，提供友好的界面与用户进行交互。在`Android`开发中通常将`Activity`或者`Fragment`作为`View`层。
2.  `Model`: 对于`Model`层也是数据层。它区别于`MVC`架构中的`Model`，在这里不仅仅只是数据模型。在`MVP`架构中`Model`它负责对数据的存取操作，例如对数据库的读写，网络的数据的请求等。
3.  `Presenter`: 对于`Presenter`层他是连接`View`层与`Model`层的桥梁并对业务逻辑进行处理。在`MVP`架构中`Model`与`View`无法直接进行交互。所以在`Presenter`层它会从`Model`层获得所需要的数据，进行一些适当的处理后交由`View`层进行显示。这样通过`Presenter`将View与`Model`进行隔离，使得`View`和`Model`之间不存在耦合，同时也将业务逻辑从`View`中抽离。

下面通过MVP结构图来看一下MVP中各个层次之间的关系。  
![MVP架构][MVP]  
在`MVP`架构中将这三层分别抽象到各自的接口当中。通过接口将层次之间进行隔离，而`Presenter`对`View`和`Model`的相互依赖也是依赖于各自的接口。这点符合了接口隔离原则，也正是面向接口编程。在`Presenter`层中包含了一个`View`接口，并且依赖于`Model`接口，从而将`Model`层与`View`层联系在一起。而对于`View`层会持有一个`Presenter`成员变量并且只保留对`Presenter`接口的调用，具体业务逻辑全部交由`Presenter`接口实现类中处理。

### 三、Demo演示 ###

实现一个模拟下载过程的操作，Demo下载地址：[Gitee][]  
动画演示过程如下：  
![MVP Demo][]  
通过点击底部的按键，来实现下载进度、下载进度展示图片、进图条以及各个按键的变化。

### 四、Demo分析 ###

运用`MVP`架构思想，`View`层就是`MainActivity`，负责`UI`的更新；`Model`层是`DownloadUtil`下载模块，负责文件的模拟下载；`Persenter`层就是代码中的`PersenterImpl`文件，负责`View`层及`Model`数据交互。另外`StatusMsg`为用户自定义的消息码。  
AS工程目录结构：  
![AS工程目录结构][AS]

### 五、Demo代码实现 ###

1.  首先编写布局文件  
    效果图如下：  
    ![布局文件效果图][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0Ftb3NzdGFu_size_16_color_FFFFFF_t_70_pic_center]  
    xml文件代码：

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:id="@+id/linearlayout_ancestor" android:background="@color/colorLightBlue" tools:context=".MainActivity">
    
        <LinearLayout android:id="@+id/linearlayout_outline_border" android:background="@color/colorSnow" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginLeft="5dp" android:layout_marginRight="5dp" android:layout_marginTop="5dp" android:layout_marginBottom="5dp">
    
            <LinearLayout android:id="@+id/linearlayout_show_title" android:layout_width="match_parent" android:layout_height="wrap_content" android:background="@color/colorPeachPuff" android:layout_marginTop="20dp" android:layout_marginLeft="20dp" android:layout_marginRight="20dp">
    
                <TextView android:id="@+id/tv_show_title" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/show_title_info" android:gravity="center_horizontal" android:textSize="24sp" android:textStyle="bold" />
    
            </LinearLayout>
    
            <LinearLayout android:id="@+id/linearlayout_download_info" android:orientation="horizontal" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="50dp" android:layout_marginLeft="30dp" android:layout_marginRight="30dp">
    
                <LinearLayout android:id="@+id/linearlayout_download_info_download_progress_textview" android:layout_weight="1" android:layout_gravity="center" android:layout_width="wrap_content" android:layout_height="wrap_content">
    
                    <TextView android:id="@+id/tv_download_progress" android:layout_width="wrap_content" android:layout_height="match_parent" android:text="@string/download_progress_title" android:textColor="@color/colorHotPink" android:gravity="center" android:textSize="18sp" android:textStyle="bold" />
                </LinearLayout>
    
                <LinearLayout android:id="@+id/linearlayout_show_download_progress" android:layout_weight="1" android:layout_gravity="center" android:layout_width="wrap_content" android:layout_height="wrap_content">
    
                    <TextView android:id="@+id/tv_show_download_progress" android:layout_width="wrap_content" android:layout_height="match_parent" android:text="@string/download_progress" android:textColor="@color/colorMediumOrchid1" android:textSize="18sp" android:textStyle="bold" />
                </LinearLayout>
    
                <LinearLayout android:id="@+id/linearlayout_show_download_status_image" android:layout_weight="1" android:layout_gravity="center" android:layout_width="wrap_content" android:layout_height="wrap_content">
    
                    <ImageView android:id="@+id/iv_show_download_status" android:layout_width="wrap_content" android:layout_height="wrap_content" android:src="@mipmap/download_init"/>
                </LinearLayout>
    
            </LinearLayout>
    
            <LinearLayout android:id="@+id/linearlayout_show_progressbar_progress" android:orientation="horizontal" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="30dp" android:layout_marginLeft="30dp" android:layout_marginRight="30dp">
    
                <ProgressBar android:id="@+id/pb_show_show_progressbar_progress" android:layout_width="match_parent" android:layout_height="10dp" android:progress="0" android:background="@color/colorAzure2" style="@style/MyProgressBar" />
            </LinearLayout>
    
    
            <RelativeLayout android:id="@+id/relativeLayout" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginTop="20dp" android:layout_marginBottom="10dp" android:layout_marginLeft="10dp" android:layout_marginRight="10dp">
    
                <LinearLayout android:id="@+id/linearlayout_button_area" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentBottom="true">
    
                    <LinearLayout android:id="@+id/linearlayout_button_area_1" android:layout_weight="1" android:orientation="vertical" android:background="@color/colorHoneydew1" android:layout_width="wrap_content" android:layout_height="wrap_content">
    
                        <Button android:id="@+id/btn_start" android:background="@color/colorHoneydew1" android:layout_gravity="center_horizontal" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/download_btn_start"/>
                    </LinearLayout>
    
                    <LinearLayout android:id="@+id/linearlayout_button_area_2" android:layout_weight="1" android:background="@color/colorThistle1" android:layout_width="wrap_content" android:layout_height="wrap_content">
    
                        <Button android:id="@+id/btn_pause" android:background="@color/colorThistle1" android:layout_gravity="center_horizontal" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/download_btn_pause"/>
                    </LinearLayout>
    
                    <LinearLayout android:id="@+id/linearlayout_button_area_3" android:layout_weight="1" android:background="@color/colorHoneydew1" android:layout_width="wrap_content" android:layout_height="wrap_content">
    
                        <Button android:id="@+id/btn_goon" android:background="@color/colorHoneydew1" android:layout_gravity="center_horizontal" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/download_btn_goon"/>
                    </LinearLayout>
    
                    <LinearLayout android:id="@+id/linearlayout_button_area_4" android:layout_weight="1" android:background="@color/colorThistle1" android:layout_width="wrap_content" android:layout_height="wrap_content">
    
                        <Button android:id="@+id/btn_stop" android:background="@color/colorThistle1" android:layout_gravity="center_horizontal" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/download_btn_stop"/>
                    </LinearLayout>
                </LinearLayout>
    
            </RelativeLayout>
    
        </LinearLayout>
    
    </LinearLayout>

1.  定义Interface  
    MainContract代码如下：

package com.example.downloadmvpdemo;
    
    
    import android.view.View;
    
    public interface MainContract { 
    
    
        /** * @MainView 用于MainActivity中 * */
        interface MainView { 
    
            void onTextViewShowProgress(int progress);        // TextView 显示下载的进度(范围：0% - 100%)
            void onImageViewShowDownloadStatus(int status);   // ImageView 显示下载状态图片(四种显示状态：初始化、下载中、下载停止、下载结束)
            void onProgressBarStep(int step);                 // ProgressBar 下载进度显示
            void onDownloadFinished();                          // 下载结束通知
        }
    
        /** * @DownloadUtil 用于DownloadUtilImpl中 * */
        interface DownloadUtil { 
    
            /** * @onDownloadListener 用于PersenterImpl中 * */
            interface onDownloadListener {               // 下载监听
                void onDownloadStart();                 // 开始下载
                void onDownloadPause(int progress);     // 暂停下载
                void onDownloadFinish();                // 下载结束
                void onDownloadProgress(int progress);  // 下载结束
            }
    
            void startDownload(onDownloadListener downloadListener); // 开始下载
            void pauseDownload(onDownloadListener downloadListener); // 暂停下载
            void stopDownload(onDownloadListener downloadListener);  // 停止下载
        }
    
        /** * @Persenter 用于PersenterImpl中 * */
        interface Persenter { 
            void onButtonClick(View view); // 按键点击事件
        }
    }

1.  定义StatusMsg类  
    StatusMsg.java文件代码如下：

package com.example.downloadmvpdemo;
    
    public class StatusMsg { 
    
        public static final int IMAGE_DOWNLOAD_STATUS_INIT   = 0X00; // Image 初始化
        public static final int IMAGE_DOWNLOAD_STATUS_START  = 0X01; // Image 开始
        public static final int IMAGE_DOWNLOAD_STATUS_STOP   = 0X02; // Image 停止
        public static final int IMAGE_DOWNLOAD_STATUS_FINISH = 0X03; // Image 结束
    
        public static final int UPDATE_TEXTVIEW_DOWNLOAD_PROGRESS = 0X04; // TextView 显示更新
        public static final int UPDATE_IMAGEVIEW_DOWNLOAD_STATUS  = 0X05; // ImageView 显示更新
        public static final int UPDATE_PROGRESSBAR_DOWNLOAD_STEP  = 0X06; // ProgressBar 显示更新
    
        public static final int BUTTON_CLICK_START = 0X07; // Button 开始
        public static final int BUTTON_CLICK_PAUSE = 0X08; // Button 暂停
        public static final int BUTTON_CLICK_STOP  = 0X09; // Button 停止
        public static final int BUTTON_CLICK_INIT  = 0X10; // Button 初始化
    
        public static final int UI_INIT        = 0X100; // UI 界面初始化
        public static final int UI_BUTTON_INIT = 0X101; // UI Button 界面初始化
    }

1.  完善DownloadUtilImpl类  
    DownloadUtilImpl.java代码如下：

package com.example.downloadmvpdemo;
    
    import android.util.Log;
    
    import java.util.Timer;
    import java.util.TimerTask;
    
    public class DownloadUtilImpl implements MainContract.DownloadUtil { 
        // Log tag
        private static final String LOG_TAG = "DownloadUtilImpl";
    
        // Download Progress
        private int mProgress = 0;
    
        // Timer
        private Timer mTimer = null;
        private int TIMER_DELAY  = 1000;
        private int TIMER_PERIOD = 1000;
    
        @Override
        public void startDownload(final onDownloadListener downloadListener) { 
            downloadListener.onDownloadStart();
            downloadListener.onDownloadProgress(mProgress);
            if (mTimer == null) { 
                mTimer = new Timer();
            }
    
            mTimer.schedule(new TimerTask() { 
                @Override
                public void run() { 
                    if (mProgress < 100) { 
                        mProgress += 10;
                    }
                    downloadListener.onDownloadProgress(mProgress);
                    if (mProgress == 100) { 
                        downloadListener.onDownloadFinish();
                        mProgress = 0;
                        mTimer.cancel();
                        mTimer = null;
                    }
                }
            }, TIMER_DELAY, TIMER_PERIOD);
        }
    
        @Override
        public void pauseDownload(onDownloadListener downloadListener) { 
            DEBUG("pauseDownload: " + mProgress);
            if (mTimer != null) { 
                mTimer.cancel();
                mTimer = null;
            }
            downloadListener.onDownloadPause(mProgress);
        }
    
        @Override
        public void stopDownload(onDownloadListener downloadListener) { 
            if (mTimer != null) { 
                mTimer.cancel();
                mTimer = null;
            }
            mProgress = 0;
            DEBUG("stopDownload: " + mProgress);
        }
    
        private void DEBUG(String info) { 
            Log.d(LOG_TAG, info);
        }
    }

1.  完善PersenterImpl类  
    PersenterImpl.java代码如下：

package com.example.downloadmvpdemo;
    
    import android.util.Log;
    import android.view.View;
    
    import com.example.downloadmvpdemo.MainContract.DownloadUtil;
    import com.example.downloadmvpdemo.MainContract.MainView;
    
    public class PersenterImpl implements MainContract.Persenter, DownloadUtil.onDownloadListener { 
    
        // Log tag
        private static final String LOG_TAG = "PersenterImpl";
    
        // MainView
        private MainView mainView = null;
    
        // downloadUtil
        private DownloadUtil downloadUtil = null;
    
        // flag
        private boolean isDownloading = false;
    
        public PersenterImpl(MainView mainView, DownloadUtil downloadUtil) { 
            this.mainView     = mainView;
            this.downloadUtil = downloadUtil;
        }
    
    
        @Override
        public void onDownloadStart() { 
            isDownloading = true;
            mainView.onImageViewShowDownloadStatus(StatusMsg.IMAGE_DOWNLOAD_STATUS_START);
        }
    
        @Override
        public void onDownloadPause(int progress) { 
            isDownloading = false;
            mainView.onImageViewShowDownloadStatus(StatusMsg.IMAGE_DOWNLOAD_STATUS_STOP);
        }
    
        @Override
        public void onDownloadFinish() { 
            isDownloading = false;
            mainView.onImageViewShowDownloadStatus(StatusMsg.IMAGE_DOWNLOAD_STATUS_FINISH);
            mainView.onDownloadFinished();
        }
    
        @Override
        public void onDownloadProgress(int progress) { 
            mainView.onTextViewShowProgress(progress);
            mainView.onProgressBarStep(progress);
        }
    
        @Override
        public void onButtonClick(View view) { 
            switch (view.getId()) { 
                case R.id.btn_start:
                case R.id.btn_goon:
                    DEBUG("Start");
                    if (!isDownloading) { 
                        DEBUG("Start enter");
                        isDownloading = true;
                        downloadUtil.startDownload(this);
                    }
                    break;
                case R.id.btn_pause:
                    DEBUG("Pause");
                    if (isDownloading) { 
                        DEBUG("Pause enter");
                        isDownloading = false;
                        downloadUtil.pauseDownload(this);
                    }
                    break;
                case R.id.btn_stop:
                    DEBUG("Stop");
                    downloadUtil.stopDownload(this);
                    isDownloading = false;
                    break;
                default:
                    break;
            }
        }
    
        private void DEBUG(String info) { 
            Log.d(LOG_TAG, info);
        }
    }

1.  完善MainActivity  
    MainActivity.java代码如下：

package com.example.downloadmvpdemo;
    
    import android.os.Bundle;
    import android.os.Handler;
    import android.os.Message;
    import android.util.Log;
    import android.view.View;
    import android.widget.Button;
    import android.widget.ImageView;
    import android.widget.ProgressBar;
    import android.widget.TextView;
    
    import androidx.annotation.NonNull;
    import androidx.annotation.Nullable;
    import androidx.appcompat.app.AppCompatActivity;
    
    public class MainActivity extends AppCompatActivity implements MainContract.MainView { 
        // Log tag
        private static final String LOG_TAG = "MainActivity";
    
        // TextView
        private TextView mTextViewDownloadProgress = null;
    
        // ImageView
        private ImageView mImageViewDownloadStatus = null;
    
        // ProgressBar
        private ProgressBar mProgressBarDownloadStep = null;
    
        // Button
        private Button mButtonStart = null;
        private Button mButtonStop  = null;
        private Button mButtonGoon  = null;
        private Button mButtonPause = null;
    
        // UIHandler
        private UIHandler mUIHandler = new UIHandler();
    
        //
        private MainContract.Persenter persenter = null;
    
        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            DEBUG("onCreate.");
    
            initView();
    
            persenter = new PersenterImpl(this, new DownloadUtilImpl());
        }
    
        private void initView() { 
            DEBUG("initView.");
    
            mTextViewDownloadProgress = findViewById(R.id.tv_show_download_progress);
            mImageViewDownloadStatus  = findViewById(R.id.iv_show_download_status);
            mProgressBarDownloadStep  = findViewById(R.id.pb_show_show_progressbar_progress);
    
            mButtonStart = findViewById(R.id.btn_start);
            mButtonStop  = findViewById(R.id.btn_stop);
            mButtonGoon  = findViewById(R.id.btn_goon);
            mButtonPause = findViewById(R.id.btn_pause);
    
            mButtonStart.setOnClickListener(new ButtonListener());
            mButtonStop.setOnClickListener(new ButtonListener());
            mButtonGoon.setOnClickListener(new ButtonListener());
            mButtonPause.setOnClickListener(new ButtonListener());
    
            mButtonPause.setEnabled(false);
            mButtonGoon.setEnabled(false);
        }
    
        private void updateTextView(int progress) { 
            mTextViewDownloadProgress.setText(progress + "%");
        }
    
        private void updateImageView(int status) { 
            switch (status) { 
                case StatusMsg.IMAGE_DOWNLOAD_STATUS_INIT:
                    mImageViewDownloadStatus.setImageDrawable(getDrawable(R.mipmap.download_init));
                    break;
                case StatusMsg.IMAGE_DOWNLOAD_STATUS_START:
                    mImageViewDownloadStatus.setImageDrawable(getDrawable(R.mipmap.download_ing));
                    break;
                case StatusMsg.IMAGE_DOWNLOAD_STATUS_STOP:
                    mImageViewDownloadStatus.setImageDrawable(getDrawable(R.mipmap.download_pause));
                    break;
                case StatusMsg.IMAGE_DOWNLOAD_STATUS_FINISH:
                    mImageViewDownloadStatus.setImageDrawable(getDrawable(R.mipmap.download_success));
                    break;
                    default:
                        break;
            }
        }
    
        private void uiInit() { 
            mTextViewDownloadProgress.setText(R.string.download_progress);
            mImageViewDownloadStatus.setImageDrawable(getDrawable(R.mipmap.download_init));
            mProgressBarDownloadStep.setProgress(0);
        }
    
        private void uiButtonInit() { 
            mButtonStart.setEnabled(true);
            mButtonPause.setEnabled(false);
            mButtonGoon.setEnabled(false);
        }
    
        private void updateProgressBar(int step) { 
            mProgressBarDownloadStep.setProgress(step);
        }
    
        @Override
        public void onTextViewShowProgress(int progress) { 
            Message message = new Message();
            message.what = StatusMsg.UPDATE_TEXTVIEW_DOWNLOAD_PROGRESS;
            message.arg1 = progress;
            mUIHandler.sendMessage(message);
        }
    
        @Override
        public void onImageViewShowDownloadStatus(int status) { 
            Message message = new Message();
            message.what = StatusMsg.UPDATE_IMAGEVIEW_DOWNLOAD_STATUS;
            message.arg1 = status;
            mUIHandler.sendMessage(message);
        }
    
        @Override
        public void onProgressBarStep(int step) { 
            Message message = new Message();
            message.what = StatusMsg.UPDATE_PROGRESSBAR_DOWNLOAD_STEP;
            message.arg1 = step;
            mUIHandler.sendMessage(message);
        }
    
        @Override
        public void onDownloadFinished() { 
            Message message = new Message();
            message.what = StatusMsg.UI_BUTTON_INIT;
            mUIHandler.sendMessage(message);
        }
    
    
        class UIHandler extends Handler { 
            @Override
            public void handleMessage(@NonNull Message msg) { 
                super.handleMessage(msg);
    
                switch (msg.what) { 
                    case StatusMsg.UI_INIT:
                        uiInit();
                        uiButtonInit();
                        break;
                    case StatusMsg.UI_BUTTON_INIT:
                        uiButtonInit();
                        break;
                    case StatusMsg.UPDATE_TEXTVIEW_DOWNLOAD_PROGRESS:
                        updateTextView(msg.arg1);
                        break;
                    case StatusMsg.UPDATE_IMAGEVIEW_DOWNLOAD_STATUS:
                        updateImageView(msg.arg1);
                        break;
                    case StatusMsg.UPDATE_PROGRESSBAR_DOWNLOAD_STEP:
                        updateProgressBar(msg.arg1);
                        break;
                        default:
                            break;
                }
            }
        }
    
        class ButtonListener implements View.OnClickListener { 
    
            @Override
            public void onClick(View view) { 
                persenter.onButtonClick(view);
                switch (view.getId()) { 
                    case R.id.btn_start:
                        mButtonStart.setEnabled(false);
    
                        mButtonPause.setEnabled(true);
                        mButtonGoon.setEnabled(false);
                        break;
                    case R.id.btn_pause:
                        mButtonPause.setEnabled(false);
                        mButtonStart.setEnabled(false);
                        mButtonGoon.setEnabled(true);
                        break;
                    case R.id.btn_goon:
                        mButtonPause.setEnabled(true);
                        mButtonStart.setEnabled(false);
                        mButtonGoon.setEnabled(false);
                        break;
                    case R.id.btn_stop:
                        mButtonStart.setEnabled(true);
                        mButtonPause.setEnabled(false);
                        mButtonGoon.setEnabled(false);
    
                        Message message = new Message();
                        message.what = StatusMsg.UI_INIT;
                        mUIHandler.sendMessage(message);
                        break;
                        default:
                            break;
                }
            }
        }
    
        private void DEBUG(String info) { 
            Log.d(LOG_TAG, info);
        }
    }

### 六、总结 ###

1.  由上面Demo代码可见，View只负责UI界面更新，Model只负责数据部分，Persenter作为View和Model的桥梁，在中间进行数据通讯。
2.  MVP代码的本质就是CallBack的使用，详见另一篇文章：[Java回调方法(CallBack)][Java_CallBack]。

[MVP]: /images/20221022/6f8eb30354194e04ab900604a4e32e46.png
[Gitee]: https://gitee.com/amosstan/DownloadMVPDemo.git
[MVP Demo]: /images/20221022/117240d3cf4a4a3aa3414d042950914d.png
[AS]: /images/20221022/4b9ac0683dfc4b559212835d673d63a1.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0Ftb3NzdGFu_size_16_color_FFFFFF_t_70_pic_center]: /images/20221022/215731332f16466881dfb5aa2b5a048d.png
[Java_CallBack]: https://blog.csdn.net/Amosstan/article/details/114963704