[英]App crashes while while creating SQLite database
I'm a new developer and a facing a problem while trying to create a database. 我是一名新开发人员,在尝试创建数据库时遇到问题。 The app runs well when the specific code line is missing. 当缺少特定的代码行时,该应用程序运行良好。 What am I doing wrong? 我究竟做错了什么?
And another question: how can i acsses the database from a fragment??? 另一个问题:我如何从片段访问数据库?
Thanks! 谢谢!
import android.app.SearchManager;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends ActionBarActivity {
SQLiteDatabase db=openOrCreateDatabase("MyDB", MODE_PRIVATE,null);
// it crashes when I add this line
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Intent intent = getIntent();
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
LOGCAT: logcat的:
04-15 18:58:42.034: E/Trace(2497): error opening trace file: No such file or directory (2)
04-15 18:58:42.178: D/AndroidRuntime(2497): Shutting down VM
04-15 18:58:42.178: W/dalvikvm(2497): threadid=1: thread exiting with uncaught exception (group=0xa630a288)
04-15 18:58:42.194: E/AndroidRuntime(2497): FATAL EXCEPTION: main
04-15 18:58:42.194: E/AndroidRuntime(2497): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.craftyonhand.www/com.craftyonhand.www.MainActivity}: java.lang.NullPointerException
04-15 18:58:42.194: E/AndroidRuntime(2497): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
04-15 18:58:42.194: E/AndroidRuntime(2497): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
04-15 18:58:42.194: E/AndroidRuntime(2497): at android.app.ActivityThread.access$600(ActivityThread.java:130)
04-15 18:58:42.194: E/AndroidRuntime(2497): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
04-15 18:58:42.194: E/AndroidRuntime(2497): at android.os.Handler.dispatchMessage(Handler.java:99)
04-15 18:58:42.194: E/AndroidRuntime(2497): at android.os.Looper.loop(Looper.java:137)
04-15 18:58:42.194: E/AndroidRuntime(2497): at android.app.ActivityThread.main(ActivityThread.java:4745)
04-15 18:58:42.194: E/AndroidRuntime(2497): at java.lang.reflect.Method.invokeNative(Native Method)
04-15 18:58:42.194: E/AndroidRuntime(2497): at java.lang.reflect.Method.invoke(Method.java:511)
04-15 18:58:42.194: E/AndroidRuntime(2497): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-15 18:58:42.194: E/AndroidRuntime(2497): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-15 18:58:42.194: E/AndroidRuntime(2497): at dalvik.system.NativeStart.main(Native Method)
04-15 18:58:42.194: E/AndroidRuntime(2497): Caused by: java.lang.NullPointerException
04-15 18:58:42.194: E/AndroidRuntime(2497): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:215)
04-15 18:58:42.194: E/AndroidRuntime(2497): at com.craftyonhand.www.MainActivity.<init>(MainActivity.java:14)
04-15 18:58:42.194: E/AndroidRuntime(2497): at java.lang.Class.newInstanceImpl(Native Method)
04-15 18:58:42.194: E/AndroidRuntime(2497): at java.lang.Class.newInstance(Class.java:1319)
04-15 18:58:42.194: E/AndroidRuntime(2497): at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
04-15 18:58:42.194: E/AndroidRuntime(2497): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
04-15 18:58:42.194: E/AndroidRuntime(2497): ... 11 more
04-15 18:59:13.598: I/Process(2497): Sending signal. PID: 2497 SIG: 9
You are initializing it too early. 您太早初始化了。 Move the init code to onCreate()
where the activity is a valid context. 将初始化代码移动到onCreate()
,其中活动是有效的上下文。
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