Question

我之前使用过ASyncTask并且没有遇到任何问题。我不明白为什么这段代码不起作用。我必须访问ftp服务器才能下载我设置为TextView的文本文件。 ASyncTask中的代码工作正常。我检查了一下。出于某种原因，当我调用新线程＆＃39; new GetStory（）时，我遇到了问题。执行＆＃39;。任何帮助都会很棒。

package com.amazingstories;

import it.sauronsoftware.ftp4j.FTPAbortedException;
import it.sauronsoftware.ftp4j.FTPClient;
import it.sauronsoftware.ftp4j.FTPDataTransferException;
import it.sauronsoftware.ftp4j.FTPDataTransferListener;
import it.sauronsoftware.ftp4j.FTPException;
import it.sauronsoftware.ftp4j.FTPIllegalReplyException;

import java.io.File;
import java.io.IOException;

import android.app.Activity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.view.Window;
import android.view.WindowManager;
import android.widget.TextView;
import android.widget.Toast;

public class DisplayStory extends Activity {

    String path;
    TextView story;
    FTPClient ftp = new FTPClient();
    File file;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        path = getIntent().getExtras().getString("path");
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(R.layout.displaystory);
        story = (TextView) findViewById(R.id.tvStory);
        story.setText(path);
        file = new File(
                Environment
                        .getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS),
                "temp.txt");    
        new GetStory().execute();
//      try{
//      new GetStory().execute();
//      }catch(Exception e){
//          Toast.makeText(getApplicationContext(), e.toString(),
//                  Toast.LENGTH_SHORT).show();
//          
//      }
    }   

    public class GetStory extends AsyncTask<Void, Integer, Void> {

        @Override
        protected Void doInBackground(Void... params) {
            // TODO Auto-generated method stub
            Toast.makeText(getApplicationContext(), "Try",
                    Toast.LENGTH_SHORT).show();
            try {
                Toast.makeText(getApplicationContext(), "Try",
                        Toast.LENGTH_SHORT).show();

                if (!ftp.isConnected()) {

                    ftp.connect(".....");
                    Toast.makeText(getApplicationContext(),
                            "connected to server", Toast.LENGTH_SHORT).show();
                    ftp.login("....", ".....");
                }
                Toast.makeText(getApplicationContext(), "FTP Connected",
                        Toast.LENGTH_SHORT).show();
                ftp.changeDirectoryUp();
                ftp.download(path, file, new FTPDataTransferListener() {

                    //ProgressDialog dialog;

                    @Override
                    public void aborted() {
                        // TODO Auto-generated method stub
                    //  dialog.dismiss();
                        story.setText("Transfer Aborted");
                    }

                    @Override
                    public void completed() {
                        // TODO Auto-generated method stub
                        //dialog.dismiss();
                    }

                    @Override
                    public void failed() {
                        // TODO Auto-generated method stub
                        //dialog.dismiss();
                        story.setText("Transfer Failed");
                    }

                    @Override
                    public void started() {
                        // TODO Auto-generated method stub
                        //dialog = ProgressDialog.show(DisplayStory.this, "",
                            //  "Loading. Please wait...", true);
                    }

                    @Override
                    public void transferred(int arg0) {
                        // TODO Auto-generated method stub

                    }

                });
                // tv.setText(test.toString());
                Toast.makeText(getApplicationContext(), "Done",
                        Toast.LENGTH_SHORT).show();
            } catch (FTPException e) {
                Toast.makeText(getApplicationContext(),
                        "Exception Caught " + e, Toast.LENGTH_LONG).show();
            } catch (IllegalStateException e) {
                // TODO Auto-generated catch block
                Toast.makeText(getApplicationContext(),
                        "Exception Caught " + e, Toast.LENGTH_LONG).show();
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                Toast.makeText(getApplicationContext(),
                        "Exception Caught " + e, Toast.LENGTH_LONG).show();
                e.printStackTrace();
            } catch (FTPIllegalReplyException e) {
                // TODO Auto-generated catch block
                Toast.makeText(getApplicationContext(),
                        "Exception Caught " + e, Toast.LENGTH_LONG).show();
                e.printStackTrace();
            } catch (FTPDataTransferException e) {
                // TODO Auto-generated catch block
                Toast.makeText(getApplicationContext(),
                        "Exception Caught " + e, Toast.LENGTH_LONG).show();
                e.printStackTrace();
            } catch (FTPAbortedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } finally {
                try {
                    ftp.logout();
                } catch (IllegalStateException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (FTPIllegalReplyException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (FTPException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            getFileData get = new getFileData();
            try {
                story.setText(get.getData(file));
                Toast.makeText(getApplicationContext(), "Set TextView",
                        Toast.LENGTH_SHORT).show();
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            file.delete();

        }

    }
}

Answer 1

   @Override
        protected Void doInBackground(Void... params) {
            // TODO Auto-generated method stub
            Toast.makeText(getApplicationContext(), "Try",
                    Toast.LENGTH_SHORT).show();

您不能在doInBackground内调用Toast。 doInBackground方法在非ui线程中运行，因此您无法在UI上操作或sidplay Toast。它必须在onPreExecute或onPostExceute中完成。

Answer 2

方法onPreExecute()，onPostExecute()和onProgressUpdate()是AsyncTask执行期间在主（UI）线程上调用的唯一方法，因此是只有您可以直接调用UI方法（例如TextView.setText()和Toast.makeText()）。

您的程序可能会崩溃，因为您无法从“未准备好循环器”的线程创建Toast，这是从doInBackground()执行此操作时发生的事情;这会导致异常和崩溃。

AsyncTask执行调试

2 个答案: