Question

我正在尝试从sqlite表获取数据到视图列表，但是当我尝试连接到数据库时，我有一个错误： 05-02 13：59：18.123：E / AndroidRuntime（714）：java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.add / admed.Listar}：java.lang.NullPointerException

我的db连接器的代码是：

  private static final String DB_NAME = "admed";
private SQLiteDatabase database;
private Basedados basedados;

public BasedadosConect(Context context) {
    basedados = new Basedados(context, DB_NAME, null, 1);
}

   public void open() throws SQLException 
   {
      //open database in reading/writing mode
      database = basedados.getWritableDatabase();
   } 

   public boolean isOpen(){
       if (database!=null){
           return true;
       } else{
           return false;
       }

   }

   public void close() 
   {
      if (database != null)
         database.close();
   }

我要打印数据的类的代码（Listar.java）：

    BasedadosConect db;
protected void onCreate(Bundle savedInstanceState) {

Intent menu = getIntent();
String tipo = menu.getStringExtra("tipo");

super.onCreate(savedInstanceState);

if (tipo.equals("medicamentos")) {
    setContentView(R.layout.medicamentos);
    db.open();
    db.insertMed(1,"trolax","trolax",2);
    db.insertMed(2,"trolex","trolex",3);

    Cursor cursor = db.getAllmeds();
    String[] values = new String[cursor.getCount()];

    if (cursor.moveToFirst())
    {                       
        for (int i = 0; i <= cursor.getCount(); i++)
        {
            values[i] = cursor.getString(2);
            cursor.moveToNext();
        }           
    }

    db.close();
    final ListView listview = (ListView) findViewById(R.id.listView1);

    final ArrayList<String> list = new ArrayList<String>();
    for (int i = 0; i < values.length; ++i) {
      list.add(values[i]);
    }
    final StableArrayAdapter adapter = new StableArrayAdapter(this,
        android.R.layout.simple_list_item_1, list);
    listview.setAdapter(adapter);


    Button medicamentos = (Button) findViewById(R.id.button1);
    medicamentos.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {
            Intent medsIntent = new Intent(view.getContext(), Editar.class);
            medsIntent.putExtra("tipo", "medicamentos");
            medsIntent.putExtra("accao", "Adicionar");
            startActivity(medsIntent);
        }
    });
}

Button voltar = (Button) findViewById(R.id.button2);
voltar.setOnClickListener(new View.OnClickListener() {
    public void onClick(View view) {
        Intent myIntent = new Intent(view.getContext(), MainActivity.class);
        startActivityForResult(myIntent, 0);
    }

});
  }

     private class StableArrayAdapter extends ArrayAdapter<String> {

    HashMap<String, Integer> mIdMap = new HashMap<String, Integer>();

    public StableArrayAdapter(Context context, int textViewResourceId,
        List<String> objects) {
      super(context, textViewResourceId, objects);
      for (int i = 0; i < objects.size(); ++i) {
        mIdMap.put(objects.get(i), i);
      }
    }
 }

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.string.app_name, menu);
    return true;
}

getAllmeds（）代码：

  public Cursor getAllmeds() 
       {
          return database.query("medicamentos", new String[]        {"medicamentos_desig"}, null, null, null, null, null);
       }

完整日志：

05-02 13:59:18.113: W/dalvikvm(714): threadid=1: thread exiting with uncaught exception (group=0x40015560)
05-02 13:59:18.123: E/AndroidRuntime(714): FATAL EXCEPTION: main
05-02 13:59:18.123: E/AndroidRuntime(714): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.add/admed.Listar}: java.lang.NullPointerException
05-02 13:59:18.123: E/AndroidRuntime(714):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
05-02 13:59:18.123: E/AndroidRuntime(714):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
05-02 13:59:18.123: E/AndroidRuntime(714):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
05-02 13:59:18.123: E/AndroidRuntime(714):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
05-02 13:59:18.123: E/AndroidRuntime(714):  at android.os.Handler.dispatchMessage(Handler.java:99)
05-02 13:59:18.123: E/AndroidRuntime(714):  at android.os.Looper.loop(Looper.java:123)
05-02 13:59:18.123: E/AndroidRuntime(714):  at android.app.ActivityThread.main(ActivityThread.java:3683)
05-02 13:59:18.123: E/AndroidRuntime(714):  at java.lang.reflect.Method.invokeNative(Native Method)
05-02 13:59:18.123: E/AndroidRuntime(714):  at java.lang.reflect.Method.invoke(Method.java:507)
05-02 13:59:18.123: E/AndroidRuntime(714):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
05-02 13:59:18.123: E/AndroidRuntime(714):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
05-02 13:59:18.123: E/AndroidRuntime(714):  at dalvik.system.NativeStart.main(Native Method)
05-02 13:59:18.123: E/AndroidRuntime(714): Caused by: java.lang.NullPointerException
05-02 13:59:18.123: E/AndroidRuntime(714):  at admed.Listar.onCreate(Listar.java:34)
05-02 13:59:18.123: E/AndroidRuntime(714):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-02 13:59:18.123: E/AndroidRuntime(714):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
05-02 13:59:18.123: E/AndroidRuntime(714):  ... 11 more

我做错了什么？提前谢谢！

Answer 1

您正在调用另一个类的非静态方法。因此，您需要在调用该类的成员函数之前初始化类对象。仅凭对象声明还不够。

在db.open（）之前插入此行;在Listar.Java的onCreate（）中。

db = new BasedadosConect(this);

从数组打印数据到Android列表

1 个答案: