如何更新异步任务中的进度条
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【中文标题】如何更新异步任务中的进度条【英文标题】:How to update progress bar in Async Task 【发布时间】:2014-11-16 07:46:40 【问题描述】:我正在为 android 构建一个简单的备份应用程序,此代码读取手机内存中的所有消息并将其存储到一个 csv 文件中,最初我显示的是一个不确定的进度条,但该应用程序的用户可能会不耐烦那个(如果他们的消息太多)所以我想添加一个确定的水平进度条来向他们展示实际的进度,我一直在尝试这样做一段时间,但我做错了,我知道我'我应该在异步任务类中使用 onProgressUpdate 方法,但我真的不知道如何实现它,所以我遇到了很多异常,所以我尝试在没有该方法的情况下以不同的方式执行它,这就是代码如下
package daniel.idea.backup;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.res.AssetFileDescriptor;
import android.database.Cursor;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.provider.ContactsContract;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity implements OnClickListener
public ArrayList<String> smsBuffer = new ArrayList<String>();
String smsFile = "SMS"+".csv";
Integer x = 0;
static Integer Total = 0;
//Initialize the various ui elements
Button contact,msg;
ProgressDialog pb;
TextView total;
static Context mContext;
//Method to fetch and write the contacts to the .vcf file
public static String getVCF()
final String vfile = "Contacts.vcf";
Cursor phones = mContext.getContentResolver().query(
ContactsContract.CommonDataKinds.Phone.CONTENT_URI, null, null, null, null);
phones.moveToFirst();
Total = phones.getCount();
for (int i = 0; i < phones.getCount(); i++)
String lookupKey = phones.getString(phones.getColumnIndex(ContactsContract.Contacts.LOOKUP_KEY));
Uri uri = Uri.withAppendedPath(ContactsContract.Contacts.CONTENT_VCARD_URI, lookupKey);
AssetFileDescriptor fd;
try
fd = mContext.getContentResolver().openAssetFileDescriptor(uri, "r");
FileInputStream fis = fd.createInputStream();
byte[] buf = new byte[(int) fd.getDeclaredLength()];
fis.read(buf);
String VCard = new String(buf);
String path = Environment.getExternalStorageDirectory().toString() + File.separator + vfile;
FileOutputStream mFileOutputStream = new FileOutputStream(path, true);
mFileOutputStream.write(VCard.toString().getBytes());
phones.moveToNext();
Log.d("Vcard", VCard);
mFileOutputStream.close();
catch (Exception e1)
// TODO Auto-generated catch block
e1.printStackTrace();
return phones.getCount()+ " Contacts";
//This is the method used to get the sms and save them to a file
private String backupSMS()
smsBuffer.clear();
Uri mSmsinboxQueryUri = Uri.parse("content://sms");
Cursor cursor1 = mContext.getContentResolver().query(
mSmsinboxQueryUri,
new String[] "_id", "thread_id", "address", "person", "date",
"body", "type" , null, null, null);
//startManagingCursor(cursor1);
String[] columns = new String[] "_id", "thread_id", "address", "person", "date", "body",
"type" ;
if (cursor1.getCount() > 0)
String count = Integer.toString(cursor1.getCount());
Log.d("Count",count);
while (cursor1.moveToNext())
String messageId = cursor1.getString(cursor1
.getColumnIndex(columns[0]));
String threadId = cursor1.getString(cursor1
.getColumnIndex(columns[1]));
String address = cursor1.getString(cursor1
.getColumnIndex(columns[2]));
String name = cursor1.getString(cursor1
.getColumnIndex(columns[3]));
String date = cursor1.getString(cursor1
.getColumnIndex(columns[4]));
String msg = cursor1.getString(cursor1
.getColumnIndex(columns[5]));
String type = cursor1.getString(cursor1
.getColumnIndex(columns[6]));
smsBuffer.add(messageId + ","+ threadId+ ","+ address + "," + name + "," + date + " ," + msg + " ,"
+ type);
generateCSVFileForSMS(smsBuffer);
return cursor1.getCount() + "Messages";
private void generateCSVFileForSMS(ArrayList<String> list)
try
String storage_path = Environment.getExternalStorageDirectory().toString() + File.separator + smsFile;
FileWriter write = new FileWriter(storage_path);
write.append("messageId, threadId, Address, Name, Date, msg, type");
write.append('\n');
for (String s : list)
write.append(s);
write.append('\n');
write.flush();
write.close();
catch (NullPointerException e)
System.out.println("Nullpointer Exception "+e);
// e.printStackTrace();
catch (IOException e)
e.printStackTrace();
catch (Exception e)
e.printStackTrace();
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.main_activity);
mContext = MainActivity.this;
Cursor phones_total = mContext.getContentResolver().query(
ContactsContract.CommonDataKinds.Phone.CONTENT_URI, null, null, null, null);
//This gets the count of all the contacts in the phone memory
Integer total_contacts = phones_total.getCount();
contact = (Button) findViewById (R.id.bt_contacts);
msg = (Button) findViewById (R.id.bt_messages);
total = (TextView) findViewById (R.id.tv_total);
contact.setOnClickListener(this);
msg.setOnClickListener(this);
total.setText(total_contacts +" Contacts");
@Override
public void onClick(View v)
// TODO Auto-generated method stub
switch(v.getId())
case R.id.bt_contacts:
MyTask task = new MyTask();
task.execute("Param 1","Param2","Param3");
break;
case R.id.bt_messages:
SmsTask task2 = new SmsTask();
task2.execute();
public class MyTask extends AsyncTask<String, Integer, String>
@Override
protected void onPreExecute()
//make the progressDialog
pb = new ProgressDialog(MainActivity.this);
pb.setTitle("Please wait ...");
pb.setIndeterminate(false);
pb.setMessage("Backing up contacts...");
pb.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
pb.setProgress(0);
pb.setMax(100);
pb.show();
@Override
protected String doInBackground(String... arg0)
// TODO Auto-generated method stub
mContext = MainActivity.this;
String total_c = getVCF();
//Increment the progress dialog
for(int i = 0; i < Total; i++)
publishProgress(i);
return total_c;
@Override
protected void onPostExecute(String result)
// TODO Auto-generated method stub
super.onPostExecute(result);
//hide the progress bar and display a toast message
pb.dismiss();
Toast.makeText(MainActivity.this, result + " Succesfully backed up", Toast.LENGTH_LONG).show();
@Override
protected void onProgressUpdate(Integer... values)
// TODO Auto-generated method stub
super.onProgressUpdate(values);
pb.incrementProgressBy(values[0]);
values[0]++;
public class SmsTask extends AsyncTask <String,Integer,String>
protected void onPreExecute()
//show the progress bar
pb = ProgressDialog.show(MainActivity.this, "Processing",
"please wait", true);
@Override
protected String doInBackground(String... params)
// TODO Auto-generated method stub
mContext = MainActivity.this;
String total_sms = backupSMS();
return total_sms;
@Override
protected void onPostExecute(String result)
// TODO Auto-generated method stub
super.onPostExecute(result);
//hide the progress bar and display a toast
pb.dismiss();
Toast.makeText(MainActivity.this, result + " Succesfully backed up", Toast.LENGTH_LONG).show();
进度条显示,但没有更新...除此之外,代码完美无缺...请我需要有关如何在此代码中实现确定进度条的建议。谢谢
编辑:我已经完成了发布的两个答案,并且我已经重新编写了我的代码,而不是更新进度条,它只是在完成后从 0 跳到 100,请有人可以指出我在这段代码中的错误
【问题讨论】:
嘿,我知道帖子很旧,但我想出了一个(不太好)的解决方案,以防你仍然需要它或其他任何人,我只需在AsyncTask
中使用sleep(1)
。这允许主线程执行(更新进度条),因为它被AsyncTask
线程阻塞。虽然这会影响性能,但我还没有找到更好的方法,这里有更多信息 my question
【参考方案1】:
我没有看到您在代码中的任何位置更新进度条。也许是因为它周围有太多不相关的代码......
但这是你必须做的:
AsyncTask
无法通过其方法 doInBackground()
访问 UI。在执行 AsyncTask
期间,您只能从 onProgressUpdate()
函数访问 UI。您没有定义此函数,因此无法执行任何更新。
文档:onProgressUpdate()
【讨论】:
我想我们也可以从onPreExecute()
和onPostExecute()
访问用户界面。 :)
啊等等,我弄错了。我只是在考虑进度更新...:D【参考方案2】:
你想用你的进度对话框显示进度..就像一个整数..正在加载..45%
如果是这样,此链接将对您有所帮助
android how to work with asynctasks progressdialog
【讨论】:
【参考方案3】:这是一个旧帖子,但我想我会插话,看看我是否可以帮助解决它。您没有获得更新进度的原因是您必须在doInBackground()
内的主while()
循环内调用publishProgress()
。其他答案中链接的资源应详细说明如何使用publishProgress()
命令!
【讨论】:
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