从阵列打印数据到视图Android

Question

我试图从sqlite表中获取数据到视图列表，但是当我尝试连接到数据库时，出现错误： 05-02 13：59：18.123 ：E/AndroidRuntime（714）：了java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.add/admed.Listar}：显示java.lang.NullPointerException

我的分贝连接器的代码是：

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(); 
    }   

类的代码，我想打印数据（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; 
} 

个

getAllmeds（）代码：

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

完整的日志：

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 

什么，我做错了什么？提前致谢！

Answer 1

您正在调用另一个类的非静态方法。所以，你需要在调用该类的成员函数之前初始化类对象。对象声明本身不够。

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

db = new BasedadosConect(this);