Question

我正在研究ftp客户端项目。我在logcat中有以下错误。

09-25 19:51:26.884: D/MyFTPClient(9521): Connection Success
09-25 19:51:27.424: W/dalvikvm(9521): dvmFindClassByName rejecting 'UNIX Type: L8'
09-25 19:51:32.309: W/dalvikvm(9521): threadid=12: thread exiting with uncaught exception (group=0x40a89228)
09-25 19:51:32.319: E/AndroidRuntime(9521): FATAL EXCEPTION: AsyncTask #1
09-25 19:51:32.319: E/AndroidRuntime(9521): java.lang.RuntimeException: An error occured while executing doInBackground()
09-25 19:51:32.319: E/AndroidRuntime(9521):     at android.os.AsyncTask$3.done(AsyncTask.java:278)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at java.lang.Thread.run(Thread.java:864)
09-25 19:51:32.319: E/AndroidRuntime(9521): Caused by: java.lang.NullPointerException
09-25 19:51:32.319: E/AndroidRuntime(9521):     at com.example.ftpclient.MyFTPClient.listftpitems(MyFTPClient.java:112)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at com.example.ftpclient.MyFTPClient$connection_test.doInBackground(MyFTPClient.java:69)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at com.example.ftpclient.MyFTPClient$connection_test.doInBackground(MyFTPClient.java:1)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at android.os.AsyncTask$2.call(AsyncTask.java:264)
09-25 19:51:32.319: E/AndroidRuntime(9521):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
09-25 19:51:32.319: E/AndroidRuntime(9521):     ... 5 more
09-25 19:51:32.399: I/Adreno200-EGLSUB(9521): <ConfigWindowMatch:1991>: Format RGBA_8888.

我的代码是

    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.showfiles);

    lv = (ListView) findViewById(R.id.listview1);
    new connection_test().execute("");


    }

private class connection_test extends AsyncTask<String, Void,ArrayList<String>> {
       ArrayList<String> temparrlist = new ArrayList<String>();
       @Override
       protected void onPreExecute(){
           dialog = ProgressDialog.show(MyFTPClient.this,null,"Please wait...");

        }

       @Override
        protected ArrayList<String> doInBackground(String... connection) {

                temparrlist=listftpitems();
                return temparrlist;

        }

       @Override
        protected void onPostExecute(ArrayList<String> result) {
           dialog.dismiss();
           ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(MyFTPClient.this,android.R.layout.simple_list_item_1,result);
           lv.setAdapter(arrayAdapter); 

        }
    }

public ArrayList<String> listftpitems(){

    try {
         //ArrayList<String> arrayList = new ArrayList<String>();
            mFTPClient = new FTPClient();
            mFTPClient.connect("ftp.ftpaddress",21);


                boolean status = mFTPClient.login("userid", "password");
                mFTPClient.setFileType(FTP.BINARY_FILE_TYPE);
                mFTPClient.enterLocalPassiveMode();

                if (status == true) {
                    Log.d(TAG, "Connection Success");

                } else {

                    Log.d(TAG, "Connection failed");
                }

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

        final FTPFile[] files;
        try {
            files = mFTPClient.listFiles("/public_html/");
            for (FTPFile file : files) {
                String details = file.getName();
                arrayList.add(details);
                Log.d(TAG, details);
            }
        }catch (IOException e1) {
            e1.printStackTrace();
        }

    return arrayList;
    }

Answer 1

当您尝试向其中添加项目时，变量arrayList可能尚未进行实例化。在arrayList.add(details);。尝试在调用asynctask之前实例化此变量。

FTPClient应用程序

1 个答案: