在 android 上安装数据库期间，将 AsyncTask 与 Sqlite 一起使用会导致应用程序崩溃？

Question

我正在尝试 AsyncTask 使用此代码安装一个相当大的数据库：

package samples.employeedirectory;


import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.WindowManager;
import android.widget.ListAdapter;
import android.widget.ListView;

public class EmployeeList extends ListActivity {

    protected SQLiteDatabase db;
    protected Cursor cursor;
    protected ListAdapter adapter;
    protected Context context;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        grabURL();

    }

    public void grabURL() {
        new GrabURL().execute();
    }

    public void onListItemClick(ListView parent, View view, int position, long id) {
        Intent intent = new Intent(this, displayE.class);
        Cursor cursor = (Cursor) adapter.getItem(position);
        intent.putExtra("eID", cursor.getInt(cursor.getColumnIndex("eID")));
        startActivity(intent);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.pref:
                // Launch Preference activity
                Intent intent = new Intent(this, Preferences.class);
                startActivity(intent);
             break;
        }
        return true;
    }


    private class GrabURL extends AsyncTask<Object, Void, Void> {
        private ProgressDialog Dialog = new ProgressDialog(EmployeeList.this);

        protected void onPreExecute() {
            Dialog.setMessage("Downloading source..");
            Dialog.show();
        }

        protected Void doInBackground(Object ... string) {
            db = (new DatabaseHelper(EmployeeList.this)).getWritableDatabase();
            cursor = db.rawQuery("SELECT * FROM employee", new String[]{});

            return null;
        }

        protected void onPostExecute(Void unused) {
            adapter = new qCursorAdapter(EmployeeList.this, cursor);
            Dialog.dismiss();
            setListAdapter(adapter);

    }
    }
}

这是应用程序的主要活动，问题是每次我第一次运行应用程序时都会崩溃。 我不知道为什么，但这是我得到的信息。

 08-16 01:07:27.783: ERROR/WindowManager(8908): android.view.WindowLeaked: Activity samples.employeedirectory.EmployeeList has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@2afd0298 that was originally added here

SO上有很多主题讨论这个错误，但我无法完全理解它们与这个特定案例的关系。

编辑：

08-16 01:24:31.073: ERROR/AndroidRuntime(8995): FATAL EXCEPTION: AsyncTask #1
08-16 01:24:31.073: ERROR/AndroidRuntime(8995): java.lang.RuntimeException: An error occured while executing doInBackground()
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at java.util.concurrent.FutureTask.run(FutureTask.java:138)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at java.lang.Thread.run(Thread.java:1019)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at android.os.Handler.<init>(Handler.java:121)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at android.widget.Toast.<init>(Toast.java:68)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at android.widget.Toast.makeText(Toast.java:231)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at samples.employeedirectory.DatabaseHelper.onCreate(DatabaseHelper.java:42)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:126)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at samples.employeedirectory.EmployeeList$GrabURL.doInBackground(EmployeeList.java:79)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at samples.employeedirectory.EmployeeList$GrabURL.doInBackground(EmployeeList.java:1)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     ... 4 more
08-16 01:24:31.083: ERROR/WindowManager(8995): Activity samples.employeedirectory.EmployeeList has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@2afd1760 that was originally added here
08-16 01:24:31.083: ERROR/WindowManager(8995): android.view.WindowLeaked: Activity samples.employeedirectory.EmployeeList has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@2afd1760 that was originally added here
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.view.ViewRoot.<init>(ViewRoot.java:265)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.view.Window$LocalWindowManager.addView(Window.java:424)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.app.Dialog.show(Dialog.java:241)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at samples.employeedirectory.EmployeeList$GrabURL.onPreExecute(EmployeeList.java:75)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.os.AsyncTask.execute(AsyncTask.java:391)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at samples.employeedirectory.EmployeeList.grabURL(EmployeeList.java:40)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at samples.employeedirectory.EmployeeList.onCreate(EmployeeList.java:30)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1623)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1675)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.app.ActivityThread.access$1500(ActivityThread.java:121)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:943)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.os.Looper.loop(Looper.java:123)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at android.app.ActivityThread.main(ActivityThread.java:3701)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at java.lang.reflect.Method.invokeNative(Native Method)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at java.lang.reflect.Method.invoke(Method.java:507)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:862)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
08-16 01:24:31.083: ERROR/WindowManager(8995):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

我认为您正在尝试通过设置适配器来更新 onPostExecute 中的 Ui。 所以，为此你必须使用线程，所以试试这个。

EmployeeList.this.runOnUiThread(new Runnable() {
     @Override
    public void run() {
        setListAdapter(adapter);
    }
});

如果您尝试更新 UI 之外的任何内容，请使用runOnUiThread进行更新。

Answer 2

问题出在DatabaseHelper的onCreate方法中，您试图在 UI 线程之外显示Toast （它正在doInBackground中执行）。

你可以在这里发现这个：

08-16 01:24:31.073: ERROR/AndroidRuntime(8995): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at android.os.Handler.<init>(Handler.java:121)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at android.widget.Toast.<init>(Toast.java:68)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at android.widget.Toast.makeText(Toast.java:231)
08-16 01:24:31.073: ERROR/AndroidRuntime(8995):     at samples.employeedirectory.DatabaseHelper.onCreate(DatabaseHelper.java:42)