在完成几个异步任务后开始新的活动

Question

我尝试下载和解压缩文件，如果服务器上有更新，并且一切正常。 但是我只想在下载并解压缩所有文件后才打开下一个活动，而不是在开始下载时才打开下一个活动。

这是我的活动：

package com.example;

import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.os.PowerManager;
import android.os.StrictMode;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.WindowManager;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class Update extends AppCompatActivity {

    private ProgressDialog ringProgressDialog;

    private static Boolean finished = false;

    private String read(String fileName) {
        StringBuilder retString = new StringBuilder();
        String zeilenumbruch = "\n";
        BufferedReader reader = null;

        try {
            File file = new File(fileName);
            FileInputStream in = new FileInputStream(Environment.getExternalStorageDirectory().toString() + "/.example/Anleitungen/.data/Versions/" + fileName);
            reader = new BufferedReader(new InputStreamReader(in));

            String zeile;
            while ((zeile = reader.readLine()) != null) {
                retString.append(zeile);
            }
            reader.close();
        } catch (IOException ex) {
            Log.e(getPackageName(), ex.getMessage());
        }

        return retString.toString();
    }

    public static String getTextOfUrl(String uri) throws Exception {

        StringBuilder result = new StringBuilder();

        URL url = new URL(uri);

        String line = null;
        BufferedReader reader = null;
        finished = false;
        try {
            reader = new BufferedReader(new InputStreamReader(url.openStream()));

            while ((line = reader.readLine()) != null) {
                result.append(line);

            }
            return result.toString();
        } finally {
            if (reader != null) {
                reader.close();
            }
            finished = true;
        }

    }

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

        if (android.os.Build.VERSION.SDK_INT > 9) {
            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
            StrictMode.setThreadPolicy(policy);
        }

        PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
        final PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.SCREEN_DIM_WAKE_LOCK, "Updating");
        wl.acquire();
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

        AsyncTaskRunner runner = new AsyncTaskRunner();
        runner.execute();

    }

    private void downloadAndUnzipContent(String path, String urlPath) {
        String url = urlPath;
        DownloadFileAsync download = new DownloadFileAsync(path, this, new DownloadFileAsync.PostDownload() {
            @Override
            public void downloadDone(File file) {
                Log.i(getPackageName(), "file download completed");


                // check unzip file now
                Decompress unzip = new Decompress(Update.this, file, true);
                unzip.unzip();

                Log.i(getPackageName(), "File unzip completed");

            }
        });
        download.execute(url);
    }

    private void downloadContent(String path, String urlPath) {
        DownloadFileAsync download = new DownloadFileAsync(path, this, new DownloadFileAsync.PostDownload() {
            @Override
            public void downloadDone(File file) {
                Log.i(getPackageName(), "file download completed");

            }
        });
        download.execute(urlPath);
    }

    private class AsyncTaskRunner extends AsyncTask<String, String, String> {

        private String resp;

        @Override
        protected String doInBackground(String... params) {
            try {
                List<String> files = new ArrayList<String>();
                files.add("Archiv");
                files.add("Funkempfaenger");
                files.add("Funkhandsender");
                files.add("Funksender");
                files.add("Funksensoren");
                files.add("Hausautomatisierung");
                files.add("Jalousieantriebe");
                files.add("Rohrantriebe");
                files.add("SensorenKabelgebunden");
                files.add("Sonderantriebe");
                files.add("Torantriebe");
                files.add("Torsteuerungen");
                files.add("WandgeraeteKabelgebunden");

                for (int uI = 0; uI < files.size(); uI++) {
                    try {
                        String newVersion = getTextOfUrl("http://www.example.com/zip/Versions/" + files.get(uI) + ".txt");
                        int nV = Integer.parseInt(newVersion);
                        String readString = files.get(uI) + ".txt";
                        String oldVersion = read(readString);
                        int iV = Integer.parseInt(oldVersion);
                        if (iV < nV) {
                            while (!finished) {
                                Log.i(getPackageName(), "Finished = False");
                            }
                            String dlPath = Environment.getExternalStorageDirectory() + "/.example/Anleitungen/.data/" + files.get(uI) + ".zip";
                            String dlPath2 = Environment.getExternalStorageDirectory() + "/.example/Anleitungen/.data/Versions/" + files.get(uI) + ".txt";
                            downloadAndUnzipContent(dlPath, "http://www.example.com/zip/Versions/" + files.get(uI) + ".zip");
                            downloadContent(dlPath2, "http://www.example.com/zip/Versions/" + files.get(uI) + ".txt");
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                        publishProgress(e.toString());
                    }
                }

            } catch (Exception e) {
                e.printStackTrace();
            }

            return "HI!";
        }

        /*
         * (non-Javadoc)
         *
         * @see android.os.AsyncTask#onPostExecute(java.lang.Object)
         */
        @Override
        protected void onPostExecute(String result) {
            // execution of result of Long time consuming operation
            Toast.makeText(Update.this, getString(R.string.UpdateFinished), Toast.LENGTH_LONG).show();
            Intent intent = new Intent(Update.this, Home.class);
            startActivity(intent);
            finish();
        }

        /*
         * (non-Javadoc)
         *
         * @see android.os.AsyncTask#onPreExecute()
         */
        @Override
        protected void onPreExecute() {

        }

        /*
         * (non-Javadoc)
         *
         * @see android.os.AsyncTask#onProgressUpdate(Progress[])
         */
        @Override
        protected void onProgressUpdate(String... text) {
            Toast.makeText(Update.this, text[0], Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public void onBackPressed() {
        Log.i(getPackageName(), "Back pressed");
    }
}

这是我的Decompress.class ：

package com.example;

import android.content.Context;
import android.util.Log;
import android.widget.Toast;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;

public class Decompress {
    private File _zipFile;
    private InputStream _zipFileStream;
    private Context context;
    private static String ROOT_LOCATION = "/sdcard";
    private static final String TAG = "UNZIPUTIL";
    private Boolean pathNew;

    public Decompress(Context context, File zipFile, Boolean path) {
        _zipFile = zipFile;
        this.context = context;
        pathNew = path;

        if (pathNew) {
            ROOT_LOCATION = "/sdcard/.example/Anleitungen";
        }

        _dirChecker("");
    }

    public Decompress(Context context, InputStream zipFile) {
        _zipFileStream = zipFile;
        this.context = context;

        _dirChecker("");
    }

    public void unzip() {
        try  {
            Log.i(TAG, "Starting to unzip");
            InputStream fin = _zipFileStream;
            if(fin == null) {
                fin = new FileInputStream(_zipFile);
            }
            ZipInputStream zin = new ZipInputStream(fin);
            ZipEntry ze = null;
            while ((ze = zin.getNextEntry()) != null) {
                Log.v(TAG, "Unzipping " + ze.getName());

                if(ze.isDirectory()) {
                    _dirChecker(ROOT_LOCATION + "/" + ze.getName());
                } else {
                    FileOutputStream fout = new FileOutputStream(new File(ROOT_LOCATION, ze.getName()));
                    ByteArrayOutputStream baos = new ByteArrayOutputStream();
                    byte[] buffer = new byte[1024];
                    int count;

                    // reading and writing
                    while((count = zin.read(buffer)) != -1)
                    {
                        baos.write(buffer, 0, count);
                        byte[] bytes = baos.toByteArray();
                        fout.write(bytes);
                        baos.reset();
                    }

                    fout.close();
                    zin.closeEntry();
                }

            }
            zin.close();
            Log.i(TAG, "Finished unzip");
        } catch(Exception e) {
            Log.e(TAG, "Unzip Error", e);
            Toast.makeText(context, "Error while unzipping: " + e.toString(), Toast.LENGTH_LONG).show();
        }

    }

    private void _dirChecker(String dir) {
        File f = new File(dir);
        Log.i(TAG, "creating dir " + dir);

        if(dir.length() >= 0 && !f.isDirectory() ) {
            f.mkdirs();
        }
    }
}

这是我的DownloadFileAsnyc.class ：

package com.example;

import android.content.Context;
import android.os.AsyncTask;
import android.util.Log;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;

public class DownloadFileAsync extends AsyncTask<String, String, String> {

    private static final String TAG ="DOWNLOADFILE";

    public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
    private PostDownload callback;
    private Context context;
    private FileDescriptor fd;
    private File file;
    private String downloadLocation;

    public DownloadFileAsync(String downloadLocation, Context context, PostDownload callback){
        this.context = context;
        this.callback = callback;
        this.downloadLocation = downloadLocation;
    }
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected String doInBackground(String... aurl) {
        int count;

        try {
            URL url = new URL(aurl[0]);
            URLConnection connection = url.openConnection();
            connection.connect();

            int lenghtOfFile = connection.getContentLength();
            Log.d(TAG, "Length of the file: " + lenghtOfFile);

            InputStream input = new BufferedInputStream(url.openStream());
            file = new File(downloadLocation);
            FileOutputStream output = new FileOutputStream(file); //context.openFileOutput("content.zip", Context.MODE_PRIVATE);
            Log.d(TAG, "file saved at " + file.getAbsolutePath());
            fd = output.getFD();

            byte data[] = new byte[1024];
            long total = 0;
            while ((count = input.read(data)) != -1) {
                total += count;
                publishProgress(""+(int)((total*100)/lenghtOfFile));
                output.write(data, 0, count);
            }

            output.flush();
            output.close();
            input.close();
        } catch (Exception e) {}
        return null;

    }
    protected void onProgressUpdate(String... progress) {
        //Log.d(TAG,progress[0]);
    }

    @Override
    protected void onPostExecute(String unused) {
        if(callback != null) callback.downloadDone(file);
    }

    public static interface PostDownload{
        void downloadDone(File fd);
    }
}

请帮我。 对不起，我的英语不好。

谢谢。

Answer 1

每当AsyncTaskRunner完成执行其后台作业时，您就在启动新的Activity。 AsyncTaskRunner基本上只是启动多个DownloadFileAsync任务。

AsyncTaskRunner不会等待启动的任务完成。 它将仅启动它们并完成导致新活动开始的任务。

解决此问题的最佳方法是仅使用一个AsyncTask来顺序处理每个文件。 肮脏的方法是使AsyncTaskRunner等待每个DownloadFileAsync任务完成，然后再启动下一个任务。 您可以通过在每个任务上调用.get（）方法来执行此操作：

download.execute(url).get();

但这又违反了AsyncTasks的目的。