java - Android sqlite异常(exception)。无法实例化 Activity

当我在Android应用中通过实例化dbs类运行活动时，如下所示：

private final DbOpenHelper dbOpen = new DbOpenHelper(MainMonitor.this);
private final SQLiteDatabase db = dbOpen.getWritableDatabase();
private final ContentValues cv = new ContentValues();

它属于例外：

    07-10 15:33:31.581: E/AndroidRuntime(1142): FATAL EXCEPTION: main
07-10 15:33:31.581: E/AndroidRuntime(1142): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.android.analizer/com.android.analyzer.MainMonitor}: java.lang.NullPointerException
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1879)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.app.ActivityThread.access$600(ActivityThread.java:122)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.os.Looper.loop(Looper.java:137)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.app.ActivityThread.main(ActivityThread.java:4340)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at java.lang.reflect.Method.invokeNative(Native Method)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at java.lang.reflect.Method.invoke(Method.java:511)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at dalvik.system.NativeStart.main(Native Method)
07-10 15:33:31.581: E/AndroidRuntime(1142): Caused by: java.lang.NullPointerException
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:221)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:157)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at com.android.analyzer.MainMonitor.<init>(MainMonitor.java:40)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at java.lang.Class.newInstanceImpl(Native Method)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at java.lang.Class.newInstance(Class.java:1319)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.app.Instrumentation.newActivity(Instrumentation.java:1023)
07-10 15:33:31.581: E/AndroidRuntime(1142):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1870)
07-10 15:33:31.581: E/AndroidRuntime(1142):     ... 11 more

DbOpenHelper看起来像这样：

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class DbOpenHelper extends SQLiteOpenHelper {

    private static final String DB_NAME = "analyzer";
    private static final int DB_VERSION = 1;

    public static final String TABLE_NAME = "network";
    public static final String ACTIVITY = "activity";

    public static final String CREATE_TABLE_NETWORK = "CREATE TABLE "+TABLE_NAME+"(" +
            "_id integer primary key autoincrement, activity integer default 1)";

//  DbOpenHelper openHelper = null;

    public DbOpenHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
//      openHelper = new DbOpenHelper(context);

    }

    public void onCreate(SQLiteDatabase sqliteDb) {
        sqliteDb.execSQL(CREATE_TABLE_NETWORK);
        sqliteDb.execSQL("INSERT INTO network(activity) VALUES(1)");
    }

    public void onUpgrade(SQLiteDatabase sqliteDb, int i, int i2) {

    }

//  @Override
//  public void close() {
//      if (openHelper!=null) openHelper.close();
//  }

}

问题解决了，但出现了下一个问题。我将插入方法放在DbOpenHelper类中，如下所示：

    public void onCreate(SQLiteDatabase sqliteDb) {
        sqliteDb.execSQL(CREATE_TABLE_NETWORK);
//      sqliteDb.execSQL("INSERT INTO network(activity) VALUES(1)");
        ContentValues cv = new ContentValues();
        cv.put(ACTIVITY_FIELD, 1);
        sqliteDb.insert(DbOpenHelper.TABLE_NAME, null, cv);
    }

在Activity中，我试图以这种方式更新表：

                    cv.put(DbOpenHelper.ACTIVITY_FIELD, 0);
//                  db.insert(DbOpenHelper.TABLE_NAME, null, cv);
                    db.update(DbOpenHelper.TABLE_NAME, cv, null, null);

An Exception is:
07-11 15:02:47.341: E/AndroidRuntime(933): FATAL EXCEPTION: main
07-11 15:02:47.341: E/AndroidRuntime(933): java.lang.NullPointerException
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.database.sqlite.SQLiteStatement.releaseAndUnlock(SQLiteStatement.java:290)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.database.sqlite.SQLiteStatement.executeUpdateDelete(SQLiteStatement.java:96)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.database.sqlite.SQLiteDatabase.updateWithOnConflict(SQLiteDatabase.java:1810)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.database.sqlite.SQLiteDatabase.update(SQLiteDatabase.java:1761)
07-11 15:02:47.341: E/AndroidRuntime(933):  at com.android.analyzer.MainMonitor$2.onCheckedChanged(MainMonitor.java:99)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.widget.CompoundButton.setChecked(CompoundButton.java:125)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.widget.Switch.setChecked(Switch.java:517)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.widget.Switch.animateThumbToCheckedState(Switch.java:508)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.widget.Switch.stopDrag(Switch.java:498)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.widget.Switch.onTouchEvent(Switch.java:458)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.View.dispatchTouchEvent(View.java:5486)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1959)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1728)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1959)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1728)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1959)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1728)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1959)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1728)
07-11 15:02:47.341: E/AndroidRuntime(933):  at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1892)
07-11 15:02:47.341: E/AndroidRuntime(933):  at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1371)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.app.Activity.dispatchTouchEvent(Activity.java:2364)
07-11 15:02:47.341: E/AndroidRuntime(933):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1840)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.View.dispatchPointerEvent(View.java:5662)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:2863)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2442)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.os.Handler.dispatchMessage(Handler.java:99)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.os.Looper.loop(Looper.java:137)
07-11 15:02:47.341: E/AndroidRuntime(933):  at android.app.ActivityThread.main(ActivityThread.java:4340)
07-11 15:02:47.341: E/AndroidRuntime(933):  at java.lang.reflect.Method.invokeNative(Native Method)
07-11 15:02:47.341: E/AndroidRuntime(933):  at java.lang.reflect.Method.invoke(Method.java:511)
07-11 15:02:47.341: E/AndroidRuntime(933):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
07-11 15:02:47.341: E/AndroidRuntime(933):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
07-11 15:02:47.341: E/AndroidRuntime(933):  at dalvik.system.NativeStart.main(Native Method)

我发现这条线很有帮助-

at com.android.analyzer.MainMonitor$2.onCheckedChanged(MainMonitor.java:99)

似乎在dbs中没有创建表或行，这就是为什么它无法自我更新的原因。这种令人难以置信的类似拖动的sqlite有什么问题？ =）

最佳答案

仅在Activity调用后创建onCreate。所以当你打电话时
private final DbOpenHelper dbOpen = new DbOpenHelper(MainMonitor.this);
活动仍未创建。
从db选项中删除final修饰符，并在onCreate调用后以单独的方法将其初始化。

您应该这样做：

public class MainMonitor extends Activity {
private DbOpenHelper dbOpen;
private SQLiteDatabase db;
private ContentValues cv;

@Override
protected void onResume() {
    super.onResume();

    initDb();
}

private void initDb() {
    dbOpen = new DbOpenHelper(MainMonitor.this);
    db = dbOpen.getWritableDatabase();
    cv = new ContentValues();
}

//....your code

}