Android 无法启动活动组件信息

我正在制作一个可以搜索“employee”表并返回结果的应用程序。我正在使用searchdialog进行搜索。但按下搜索对话框上的搜索按钮时，我会得到FC。请帮帮我

代码：

public class SimpleSearch extends ListActivity {
    protected SQLiteDatabase db;
    protected Cursor cursor;
    protected ListAdapter adapter;
    protected String query;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Intent intent = getIntent();
        if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
          String query = intent.getStringExtra(SearchManager.QUERY);
          doMySearch(query);
          }
        }

    private void doMySearch(String query) {
        cursor = db.rawQuery("SELECT _id, firstName, lastName, title FROM employee WHERE firstName || ' ' || lastName LIKE ?", 
                  new String[]{"%" + query + "%"});
        adapter = new SimpleCursorAdapter(
                this, 
                R.layout.emp_list_item, 
                cursor, 
                new String[] {"firstName", "lastName", "title"}, 
                new int[] {R.id.firstName, R.id.lastName, R.id.title});
        setListAdapter(adapter);

    }

}

错误，堆栈跟踪：

shortMsg:java.lang.NullPointerException
longMsg:java.lang.NullPointerException: Unable to start activity ComponentInfo{com.simple.search/com.simple.search.SimpleSearch}: java.lang.NullPointerException
stackTrace:java.lang.RuntimeException: Unable to start activity ComponentInfo{com.simple.search/com.simple.search.SimpleSearch}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1664)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1680)
at android.app.ActivityThread.access$1500(ActivityThread.java:117)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3703)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.simple.search.SimpleSearch.onCreate(SimpleSearch.java:34)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1628)
... 11 more

数据库助手

public class DatabaseHelper extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "test_diectory";

    protected Context context;

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);
        this.context = context;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String s;
        try {
            Toast.makeText(context, "1", 2000).show();
            InputStream in = context.getResources().openRawResource(R.raw.sql);
            DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
            Document doc = builder.parse(in, null);
            NodeList statements = doc.getElementsByTagName("statement");
            for (int i=0; i<statements.getLength(); i++) {
                s = statements.item(i).getChildNodes().item(0).getNodeValue();
                db.execSQL(s);
            }
        } catch (Throwable t) {
            Toast.makeText(context, t.toString(), 50000).show();
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS employees");
        onCreate(db);
    }

}

public类DatabaseHelper扩展了SQLiteOpenHelper{
公共静态最终字符串数据库\u NAME=“test\u diectory”；
受保护的语境；
公共数据库助手（上下文）{
super（上下文，数据库名称，null，1）；
this.context=上下文；
}
@凌驾
public void onCreate（SQLiteDatabase db）{
字符串s；
试一试{
Toast.makeText（上下文，“1”，2000）.show（）；
InputStream in=context.getResources（）.openRawResource（R.raw.sql）；
DocumentBuilder=DocumentBuilderFactory.newInstance（）.newDocumentBuilder（）；
Document doc=builder.parse（in，空）；
节点列表语句=doc.getElementsByTagName（“语句”）；
对于（int i=0；i多亏了adil。看起来我忘记了初始化db。添加
db=（新DatabaseHelper（this））。getWritableDatabase（）；
修复了错误。
你的光标是什么getCount（）？调试它。。你能解释一下怎么做吗？我是eclipse和android新手。第34行是doMySearch（查询）；那么您的
db
在哪里声明和初始化？请参阅，在您的
SimpleSearch
中，您有一个受
保护的SQLiteDatabase db；
您在哪里初始化它。。