我在下面的代码中使用thread.join时遇到问题。它应该在执行代码之后等待线程完成，对吧？它在不同的场合表现得不同。
我有三个案例来检查我的代码是否顺利
我认为我在onCreate方法上的代码存在问题：
dropOldSchedule();
dropThread.join();
triggerDownload();
根据日志，代码在此部分之前工作......可能是什么问题？
MainActivity.java
public class MainActivity extends Activity {
final static int INDEX_ACCTTYPE = 0;
final static int INDEX_ECN = 1;
final static int INDEX_TLN = 2;
final static int INDEX_SIN = 3;
final static int INDEX_MOBILE = 4;
final static int INDEX_CITY = 5;
final static int INDEX_START_DATE = 6;
final static int INDEX_START_TIME = 7;
final static int INDEX_END_DATE = 8;
final static int INDEX_END_TIME = 9;
final static int INDEX_REASON = 10;
final static int INDEX_DETAILS = 11;
DatabaseHandler db;
String str;
ProgressDialog pd;
TextView homeText1, homeText2, homeText3, homeText4;
final private String csvFile = "http://www.meralco.com.ph/pdf/pms/pms_test.csv";
final private String uploadDateFile = "http://www.meralco.com.ph/pdf/pms/UploadDate_test.txt";
Thread dropThread = new Thread(new Runnable() {
public void run() {
db = new DatabaseHandler(MainActivity.this);
db.dropOldSchedule();
runOnUiThread(new Runnable() {
public void run() {
while (!pd.isShowing());
db.close();
pd.dismiss();
}
});
}
});
Thread getUploadDateThread = new Thread(new Runnable() {
public void run() {
try {
URL myURL = new URL(uploadDateFile);
BufferedReader so = new BufferedReader(new InputStreamReader(myURL.openStream()));
while (true) {
String output = so.readLine();
if (output != null) {
str = output;
}
else {
break;
}
}
so.close();
}
catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
runOnUiThread(new Runnable() {
public void run() {
while (!pd.isShowing());
pd.dismiss();
}
});
}
});
Thread downloadThread = new Thread(new Runnable() {
public void run() {
db = new DatabaseHandler(MainActivity.this);
db.beginTransaction();
try {
URL url = new URL(csvFile);
Log.i("dl", "start");
InputStream input = url.openStream();
CSVReader reader = new CSVReader(new InputStreamReader(input));
Log.i("dl", "after reading");
String [] sched;
while ((sched = reader.readNext()) != null) {
if(sched[INDEX_CITY].equals("")) sched[INDEX_CITY]="OTHERS";
try {
db.addRow(sched[INDEX_SIN], sched[INDEX_CITY],
sched[INDEX_START_DATE], sched[INDEX_START_TIME],
sched[INDEX_END_DATE], sched[INDEX_END_TIME],
sched[INDEX_DETAILS], sched[INDEX_REASON]);
} catch (IndexOutOfBoundsException e) {
db.addRow(sched[INDEX_SIN], sched[INDEX_CITY],
sched[INDEX_START_DATE], sched[INDEX_START_TIME],
sched[INDEX_END_DATE], sched[INDEX_END_TIME],
"", sched[INDEX_REASON]);
//e.printStackTrace();
}
}
input.close();
Log.i("dl", "finished");
} catch (MalformedURLException e) {
e.printStackTrace();
db.endTransaction();
} catch (IOException e) {
e.printStackTrace();
db.endTransaction();
}
Log.d("Count", ""+db.count());
db.setTransactionSuccessful();
db.endTransaction();
writeUploadDateInTextFile();
}
});
@SuppressWarnings("unqualified-field-access")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.pms_main);
Button home = (Button) findViewById(R.id.home);
home.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, MeralcoSuite_TabletActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
finish();
}
});
homeText1 = (TextView) findViewById(R.id.home_text1);
homeText2 = (TextView) findViewById(R.id.home_text2);
homeText3 = (TextView) findViewById(R.id.home_text3);
homeText4 = (TextView) findViewById(R.id.home_text4);
homeText1.setVisibility(View.INVISIBLE);
homeText2.setVisibility(View.INVISIBLE);
homeText3.setVisibility(View.INVISIBLE);
homeText4.setVisibility(View.INVISIBLE);
getUploadDate();
try {
getUploadDateThread.join(); //wait for upload date
Log.d("getUploadDate","thread died, upload date=" + str);
if(dbExists()){
db = new DatabaseHandler(MainActivity.this);
Log.d("Count", "" + db.count());
db.close();
if(!uploadDateEqualsDateInFile()){
dropOldSchedule();
dropThread.join();
triggerDownload();
}
showDisclaimer();
Log.i("oncreate", "finished!");
return;
}
triggerDownload();
showDisclaimer();
Log.i("oncreate", "finished!");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void dropOldSchedule(){
if(pd!=null && pd.isShowing())
pd.setTitle("Getting upload date...");
else
pd = ProgressDialog.show(this, "Getting upload date",
"This may take a few minutes...", true, false);
dropThread.start();
}
public void triggerDownload() {
if (!checkInternet()) {
showAlert("An internet connection is required to perform an update, please check that you are connected to the internet");
return;
}
if(pd!=null && pd.isShowing())
pd.setTitle("Getting upload date...");
else
pd = ProgressDialog.show(this, "Getting upload date",
"This may take a few minutes...", true, false);
downloadThread.start();
}
public void getUploadDate() {
Log.d("getUploadDate", "getting upload date of schedule");
if(pd!=null && pd.isShowing())
pd.setTitle("Getting upload date...");
else
pd = ProgressDialog.show(this, "Getting upload date",
"This may take a few minutes...", true, false);
getUploadDateThread.start();
}
public void writeUploadDateInTextFile() {
Log.d("writeUploadDateTextFile", "writing:"+str);
try {
OutputStreamWriter out = new OutputStreamWriter(openFileOutput(
"update.txt", 0));
out.write(str);
out.close();
} catch (java.io.IOException e) {
e.printStackTrace();
}
}
public void showDisclaimer() {
Log.d("ShowDisclaimer", "showing disclaimer");
homeText3
.setText("..." + str
+ "...");
homeText1.setVisibility(View.VISIBLE);
homeText2.setVisibility(View.VISIBLE);
homeText3.setVisibility(View.VISIBLE);
homeText4.setVisibility(View.VISIBLE);
Log.d("showDisclaimer", "finished showing disclaimer");
}
public boolean uploadDateEqualsDateInFile() {
Log.d("uploadDateEqualsDateInFile","comparing schedule upload dates");
try {
String recordedDate = "";
InputStream instream = openFileInput("update.txt");
if (instream != null) { // if file the available for reading
Log.d("uploadDateEqualsDateInFile","update.txt found!");
InputStreamReader inputreader = new InputStreamReader(instream);
BufferedReader buffreader = new BufferedReader(inputreader);
String line = null;
while ((line = buffreader.readLine()) != null) {
recordedDate = line;
Log.d("uploadDateEqualsDateInFile","recorded:"+recordedDate);
}
Log.d("uploadDateEqualsDateInFile","last upload date: " + str + ", recorded:" +recordedDate);
if(str.equals(recordedDate)) return true;
return false;
}
Log.d("uploadDateEqualsDateInFile","update.txt is null!");
return false;
} catch (FileNotFoundException e) {
e.printStackTrace();
return false;
} catch (IOException e) {
e.printStackTrace();
return false;
}
}
public boolean checkInternet() {
ConnectivityManager cm = (ConnectivityManager) this
.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo infos[] = cm.getAllNetworkInfo();
for (NetworkInfo info : infos)
if (info.getState() == NetworkInfo.State.CONNECTED
|| info.getState() == NetworkInfo.State.CONNECTING) {
return true;
}
return false;
}
public boolean dbExists() {
File database=getApplicationContext().getDatabasePath(DatabaseHandler.DATABASE_NAME);
if (!database.exists()) {
Log.i("Database", "Not Found");
return false;
}
Log.i("Database", "Found");
return true;
}
@Override
protected void onDestroy() {
super.onDestroy();
if (db != null) {
db.close();
}
}
@Override
protected void onPause() {
super.onPause();
if (db != null) {
db.close();
}
}
}
答案 0 :(得分：2)
抱歉，我在代码中找不到错误或问题。但我强烈建议您使用AsyncTask在不同的线程中执行某些操作。 AsyncTask非常易于使用，我想说它是java的最大优势之一。我真的很想念它。
http://labs.makemachine.net/2010/05/android-asynctask-example/
检查那些链接希望对您有所帮助。
答案 1 :(得分：1)
已经提到AsyncTask是更好的选择。但是，可能会出现这种情况，即您的加入调用将抛出InterruptedException。尝试使用它：
while(getUploadDateThread.isRunning()){
try{
getUploadDateThread.join();
} catch (InterruptedException ie){}
}
// code after join
答案 2 :(得分：0)
我认为当你在onCreate()方法中调用join时，你面临的问题是你阻止了UI线程。您应该将此代码移动到另一个应该在后台执行的线程中，一旦完成，您就可以更新UI。
以下是示例代码：
final Thread t1 = new Thread();
final Thread t2 = new Thread();
t1.start();
t2.start();
new Thread(new Runnable() {
@Override
public void run() {
// Perform all your thread joins here.
try {
t1.join();
t2.join();
} catch (Exception e) {
// TODO: handle exception
}
// This thread wont move forward unless all your threads
// mentioned above are executed or timed out.
// ------ Update UI using this method
runOnUiThread(new Runnable() {
@Override
public void run() {
// Update UI code goes here
}
});
}
}).start();
答案 3 :(得分：-1)
thread.join的重点是确保在继续当前执行之前，你所加入的任何线程上的所有进程都已完成。
如果您即将关闭某个程序并希望在结束之前确保保存等，那么这是有道理的。使用线程。加入你的onCreate并不是真的有帮助。
很抱歉，我知道这并不能解决您的疑问，但请确保您知道为什么使用thread.join！