我的活动创建了一个单独的AsyncTask类的实例并执行它。 DoInBackground在主要活动中与单独的线程一起运行良好，但onPostExecute仅在UI线程中的所有内容完成后调用。据我所知，情况并非如此：只要doInBackground完成并返回一个值，AsyncTask就应该转移到onPostExecute。这是我的代码，如果有人能告诉我这里发生了什么，我真的很感激：
首先是我的AsyncTask：
package com.theo.mcginley.comp4prototype;
import android.os.AsyncTask;
import java.sql.*;
public class DBConnector extends AsyncTask <String, Void, ResultSet> {
private Connection con;
private Statement st;
private ResultSet rs;
// public CallBackListener DBlistener;
public ResultSet getMyResults(){
return rs;
}
//public
@Override
protected ResultSet doInBackground(String... params) {
String Query = params[0];
System.out.println("Starting DBConnector");
try{
Class.forName("com.mysql.jdbc.Driver");
}catch(Exception ex){
System.out.println("Error: "+ex);
}
try{
con = DriverManager.getConnection("jdbc:mysql://musictimetables.cdo3zf9dx3fx.us-west-2.rds.amazonaws.com:3306/music?user=Admin&password=password");
st = con.createStatement();
}catch(Exception ex) {
System.out.println("Error: " + ex);
}
System.out.println("Connected");
try{
rs = st.executeQuery(Query);
System.out.println("Records from Database");
}catch(Exception ex){
System.out.println(ex);
}
System.out.println("Finished DBConnector");
if (rs==null){
System.out.println("ITS NULL");
} else{
System.out.println("ITS NOT NULL");
}
return rs;
}
@Override
protected void onPostExecute(ResultSet myrs) {
// super.onPostExecute(myrs);
System.out.println("THIS IS WHERE IT ALL GOES WRONG");
// DBlistener.processFinish(myrs);
}
}
注意 - 我必须注释掉侦听器，因为它依赖onPostExecute按预期工作
现在主要活动（相关子程序）：
private void BuildTable(int rows, int cols, String GivenTutorID) {
DBConnector connect = new DBConnector();
String StudentID = "";
String TutorID = "";
String VenueLocation = "";
String LessonDate = "";
String LessonStartTime = "";
String LessonEndTime = "";
List<String> AllTheDates = new ArrayList<String>();
Integer count = 0;
connect.execute("SELECT * FROM Lessons WHERE Lessons.TutorID = '" + GivenTutorID + "';");
try {
Thread.sleep(4000);//just used so that the resultset doesn't get no results - waits for connect.execute to finish.
} catch (Exception e) {
}
try {
Thread.sleep(4000);//just used so that the resultset doesn't get no results - waits for connect.execute to finish.
} catch (Exception e) {
}
try {
Thread.sleep(4000);//just used so that the resultset doesn't get no results - waits for connect.execute to finish.
} catch (Exception e) {
}
System.out.println("Attempting to get ResultSet");
try {
rs = connect.getMyResults();
System.out.println("so far so good");
} catch(Exception e){
System.out.println("caught exception1: " + e);
}
System.out.println("through to the other side");
System.out.println("Finished DBConnector");
if (rs==null){
System.out.println("ITS STILL NULL");
} else{
System.out.println("ITS STILL NOT NULL");
}
try {
while (rs.next()) {
StudentID = rs.getString("StudentID");
TutorID = rs.getString("TutorID");
VenueLocation = rs.getString("VenueLocation");
LessonDate = rs.getString("LessonDate");
LessonStartTime = rs.getString("LessonStartTime");
LessonEndTime = rs.getString("LessonEndTime");
AllTheDates.add(count,LessonDate);
count++;
}
}catch(Exception ex) {
System.out.println("caught exception2: " + ex + " xd xDDD " +count);
}
System.out.println("ejgwiw");
BuildRow(AllTheDates.toArray(new String[AllTheDates.size()]));
}
private void BuildRow(String...params){
TableRow row = new TableRow(this);
row.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.WRAP_CONTENT));
try {
for (Integer i = 0; i < params.length; i++) {
TextView tv = new TextView(this);
tv.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT,
LayoutParams.WRAP_CONTENT));
tv.setBackgroundResource(R.drawable.cell_shape);
tv.setPadding(5, 5, 5, 5);
tv.setText(params[i]);
System.out.println(params[i] + " run " + i);
row.addView(tv);
}
try {
tblTutorTimetable.addView(row);
} catch (Exception ex) {
System.out.println(ex);
}
} catch (Exception ex){
System.out.println(ex);
}
}
最后是logcat：
02-01 19:26:45.092 10317-10494/com.theo.mcginley.comp4prototype I/System.out﹕ Starting DBConnector
02-01 19:26:48.223 10317-10494/com.theo.mcginley.comp4prototype I/System.out﹕ Connected
02-01 19:26:48.423 10317-10494/com.theo.mcginley.comp4prototype I/System.out﹕ Records from Database
02-01 19:26:48.423 10317-10494/com.theo.mcginley.comp4prototype I/System.out﹕ Finished DBConnector
02-01 19:26:48.423 10317-10494/com.theo.mcginley.comp4prototype I/System.out﹕ ITS NOT NULL
02-01 19:26:57.462 10317-10317/com.theo.mcginley.comp4prototype I/System.out﹕ Attempting to get ResultSet
02-01 19:26:57.462 10317-10317/com.theo.mcginley.comp4prototype I/System.out﹕ so far so good
02-01 19:26:57.462 10317-10317/com.theo.mcginley.comp4prototype I/System.out﹕ through to the other side
02-01 19:26:57.462 10317-10317/com.theo.mcginley.comp4prototype I/System.out﹕ Finished DBConnector
02-01 19:26:57.462 10317-10317/com.theo.mcginley.comp4prototype I/System.out﹕ ITS STILL NOT NULL
02-01 19:26:57.482 10317-10317/com.theo.mcginley.comp4prototype I/System.out﹕ ejgwiw
02-01 19:26:57.492 10317-10317/com.theo.mcginley.comp4prototype I/System.out﹕ 2015-01-05 run 0
02-01 19:26:57.492 10317-10317/com.theo.mcginley.comp4prototype I/System.out﹕ 2015-01-05 run 1
02-01 19:26:57.492 10317-10317/com.theo.mcginley.comp4prototype I/Choreographer﹕ Skipped 757 frames! The application may be doing too much work on its main thread.
02-01 19:26:57.542 10317-10317/com.theo.mcginley.comp4prototype I/System.out﹕ THIS IS WHERE IT ALL GOES WRONG
在UI线程上的冗长进程完成后，最后一次系统输出来自onPostExecute。任何帮助将不胜感激！
答案 0 :(得分：1)
onPostExecute()实际上在主UI线程中运行 - 这样您就可以与只能在那里编辑的元素进行交互，例如TextViews上的文字，清除ProgressBar它运行的顺序取决于Android本身，尽管它往往位于线程队列的末尾。
以下是一些简单的修复：
doInBackground()内的非UI线程中执行您想要执行的操作onPostExecute()的末尾启动另一个AsyncTask并将其传递给任何必要的数据