MVP 入门 (Android demo解析)

1、mvc mvp

由于mvc下的Controller（也就是Activity）非常的臃肿，不仅要管理视图相关，还要处理一部分逻辑，于是就有了mvp的出现，将Activity看成视图，让他仅仅管理视图相关的工作，Activity不再和业务直接发生关系，
将与业务发生关系的代码从Activity中抽出，放在presenter 中。
看过别人写的关于mvp的博客，自己不写一遍，觉得还是懵懵懂懂，hongyang有一个登陆的例子，http://blog.csdn.net/lmj623565791/article/details/46596109
我觉得写的挺好的，在理解之后，我自己实现了一个demo,功能很简单就 是下载一个文件到本地，然后显示进度条，下载结束后对话框告知用户，下载出错了也会对话框提示哪里错了。

地址如下：

https://github.com/yuzhiyun/MVPDownloadFile
注意：运行demo之后，下载的文件在sd卡根目录（Environment.getExternalStorageDirectory()）下。

图解

根据自己写的demo我自己又画了一个图

包结构

代码解释

IDownloadFileView.java

这是view层的接口，view实现这个接口中对view的操作函数

public interface IDownloadFileView {
    String getUrl();
    void showErrorDialog(String error);
    void showSuccessDialog();
    void changeProgress(int progress);
}

MainActivity.java

view层，实现IView接口，实现对view的操作函数；
view关联一个presenter,并且把对IView的实现传递给presenter。这样，presenter就可以通过IView操作UI了。

public class MainActivity extends BaseActivity implements View.OnClickListener,IDownloadFileView {
    Button btn_download;
    EditText et_url;
    ProgressBar progressBar;
    DownloadPresenter downloadPresenter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    protected void setViewForActivity() {
        setContentView(R.layout.activity_main);
    }

    @Override
    protected void findViewByIds() {
        btn_download= (Button) findViewById(R.id.btn_download);
        et_url= (EditText) findViewById(R.id.et_url);
        progressBar= (ProgressBar) findViewById(R.id.progressBar);
    }

    @Override
    protected void setListeners() {
        btn_download.setOnClickListener(this);
    }

    @Override
    protected void initOther() {
        downloadPresenter=new DownloadPresenter(this);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btn_download:
                downloadPresenter.startDownLoad();
                break;
        }
    }

    /**
     * 获取下载链接
     * @return
     */
    @Override
    public String getUrl() {
//        return ;
        return et_url.getText().toString().trim();
    }

    @Override
    public void showErrorDialog(String error) {
        //Toast.makeText(this,error,Toast.LENGTH_LONG);
        //Log.i("MainActivity",error);
        showDialog(error);
    }


    @Override
    public void showSuccessDialog() {
       // Toast.makeText(MainActivity.this,"下载成功",Toast.LENGTH_LONG);
        showDialog("下载成功");
        //Log.i("MainActivity","下载成功");
    }

    @Override
    public void changeProgress(int progress) {
        progressBar.setProgress(progress);
    }
    /**
     * 弹出对话框
     *
     * @param msg
     */
    public void showDialog(String msg) {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setMessage("返回结果:\n" + msg)
                .setCancelable(false)
                .setPositiveButton("确认", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        dialog.dismiss();
                    }
                });
        builder.create().show();
    }

}

DownloadPresenter.java

presenter持有iview接口（IDownloadFileView）以及model层的业务类（IDownloadFileBiz），这样presenter先调用model 完成业务，再把反馈结果显示到UI 上。

public class DownloadPresenter {
    IDownloadFileView downloadFileView;
    IDownloadFileBiz downloadFileBiz;
    public  DownloadPresenter(IDownloadFileView iDownloadFileView){
        downloadFileView=iDownloadFileView;
        downloadFileBiz=new DownloadBiz();
    }
    public  void startDownLoad(){
        downloadFileBiz.startDownload(downloadFileView.getUrl(), new OnDownloadListener() {
            @Override
            public void OnError(String error) {
                downloadFileView.showErrorDialog(error);
            }

            @Override
            public void OnSuccess() {
                downloadFileView.showSuccessDialog();
            }

            @Override
            public void OnProgress(Integer progress) {
                downloadFileView.changeProgress(progress);
            }
        });
    }
}

DownloadBiz.java

Model层的业务类，依赖presenter传递过来的OnDownloadListener最终把执行结果反馈到UI上

public class DownloadBiz implements IDownloadFileBiz {

    @Override
    public void startDownload(String url, OnDownloadListener downloadListener) {
        new DownLoadAsynctask(downloadListener).execute(url);
    }
}
class DownLoadAsynctask extends AsyncTask<String,Integer,String>{

    OnDownloadListener downloadListener;
    DownLoadAsynctask(OnDownloadListener downloadListener){
        this.downloadListener=downloadListener;
    }
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }
    @Override
    protected String doInBackground(String... strings)   {



        double now_length=0;
        double sum_length=0;
        String filename="";
        boolean isPaused = false;
        File file = null;
        int startIndex = 0,endIndex=0;
        try {
            byte[] bytes = new byte[1024];
            URL url = null;
            HttpURLConnection conn = null;
            url = new URL(strings[0]);

            conn = (HttpURLConnection) url.openConnection();
            endIndex = conn.getContentLength();
            System.out.println("获得输入流");
            InputStream is = conn.getInputStream();
            System.out.println("输入流完毕");
            sum_length = endIndex;

            filename = strings[0].substring(strings[0].lastIndexOf("/")+1);
            file = new File(Environment.getExternalStorageDirectory(),filename);
            /**
             *  RandomAccessFile可以访问文件的任意位置
             *  "r"    以只读方式打开。调用结果对象的任何 write 方法都将导致抛出 IOException。
             *  "rw"   打开以便读取和写入。
             *  "rws"  打开以便读取和写入。相对于 "rw"，"rws" 还要求对“文件的内容”或“元数据”的每个更新都同步写入到基础存储设备。
             *  "rwd"  打开以便读取和写入，相对于 "rw"，"rwd" 还要求对“文件的内容”的每个更新都同步写入到基础存储设备。
             *  明白？
             */
            RandomAccessFile raf1 = new RandomAccessFile(file,"rwd");
            System.out.println("开始写入");
            raf1.seek(startIndex);
            now_length += startIndex;
            int i =1;
            int len =0;
            while (((len=is.read(bytes))!=-1)&&!isPaused){
                System.out.println("第"+i+"次读入");
                raf1.write(bytes, 0, len);
                System.out.println("第" + i + "次写入");
                now_length+=len;
                i++;
                publishProgress((int)(now_length/sum_length *100));
            }

            System.out.println("写入完毕");
            raf1.close();

            conn.disconnect();

        } catch (IOException e) {
            e.printStackTrace();
            return e.toString();
        }

        return "success";
    }
    @Override
    protected void onPostExecute(String s) {
        super.onPostExecute(s);

        if(s.equals("success"))
            downloadListener.OnSuccess();
        else
            downloadListener.OnError(s);
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);
        downloadListener.OnProgress(values[0]);
    }


}