Android - openOrCreateDatabase - 空指針異常

Question

我有我的類DAO，當我打電話給我的類conexao該方法返回null，但爲什麼？

public void criarBanco() { 
     Conexao conexao = new Conexao(); 
     try { 
      BANCO_DE_DADOS = conexao.abrirBanco(); // <<<<<<<<<<<<< 
      String SQL = "CREATE TABLE IF NOT EXISTS tablecadastropessoa (_id INTEGER PRIMARY KEY, nome TEXT, telefone TEXT)"; 
      BANCO_DE_DADOS.execSQL(SQL); 
     } catch (Exception e) { 
      Log.i(TAG, "Erro ao criar o banco" + e); 
     } finally { 
      //conexao.fecharBanco(BANCO_DE_DADOS); 
     } 
    } 

    // ABRIR BANCO 
    public SQLiteDatabase abrirBanco(){ 
     try { 
      BANCO_DE_DADOS = openOrCreateDatabase(NOME_BANCO, MODE_PRIVATE, null); // RETURN NULL 
     } catch (Exception e) { 
      Util.exibirMensagem("Erro ao criar o banco: " + e, AulaCadastroActivity.context); 
      Log.i(TAG, "Erro ao abrir o banco: " + e); 
     } 
     return BANCO_DE_DADOS; 
    } 

誤差

07-05 13:12:54.800: E/AndroidRuntime(223): Uncaught handler: thread main exiting due to uncaught exception 
07-05 13:12:54.811: E/AndroidRuntime(223): java.lang.RuntimeException: Unable to start activity ComponentInfo{br.cadastro/br.cadastro.AulaCadastroActivity}: java.lang.NullPointerException 
07-05 13:12:54.811: E/AndroidRuntime(223): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496) 
07-05 13:12:54.811: E/AndroidRuntime(223): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512) 
07-05 13:12:54.811: E/AndroidRuntime(223): at android.app.ActivityThread.access$2200(ActivityThread.java:119) 
07-05 13:12:54.811: E/AndroidRuntime(223): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863) 
07-05 13:12:54.811: E/AndroidRuntime(223): at android.os.Handler.dispatchMessage(Handler.java:99) 
07-05 13:12:54.811: E/AndroidRuntime(223): at android.os.Looper.loop(Looper.java:123) 
07-05 13:12:54.811: E/AndroidRuntime(223): at android.app.ActivityThread.main(ActivityThread.java:4363) 
07-05 13:12:54.811: E/AndroidRuntime(223): at java.lang.reflect.Method.invokeNative(Native Method) 
07-05 13:12:54.811: E/AndroidRuntime(223): at java.lang.reflect.Method.invoke(Method.java:521) 
07-05 13:12:54.811: E/AndroidRuntime(223): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 
07-05 13:12:54.811: E/AndroidRuntime(223): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 
07-05 13:12:54.811: E/AndroidRuntime(223): at dalvik.system.NativeStart.main(Native Method) 
07-05 13:12:54.811: E/AndroidRuntime(223): Caused by: java.lang.NullPointerException 
07-05 13:12:54.811: E/AndroidRuntime(223): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:193) 
07-05 13:12:54.811: E/AndroidRuntime(223): at br.cadastro.Conexao.abrirBanco(Conexao.java:20) 
07-05 13:12:54.811: E/AndroidRuntime(223): at br.cadastro.ContadosDAO.criarBanco(ContadosDAO.java:27) 
07-05 13:12:54.811: E/AndroidRuntime(223): at br.cadastro.AulaCadastroActivity.inicializar(AulaCadastroActivity.java:81) 
07-05 13:12:54.811: E/AndroidRuntime(223): at br.cadastro.AulaCadastroActivity.onCreate(AulaCadastroActivity.java:27) 
07-05 13:12:54.811: E/AndroidRuntime(223): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
07-05 13:12:54.811: E/AndroidRuntime(223): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459) 
07-05 13:12:54.811: E/AndroidRuntime(223): ... 11 more 

Answer 1

很可能NOME_BANCO沒有在這一行

BANCO_DE_DADOS = openOrCreateDatabase(NOME_BANCO, MODE_PRIVATE, null); 

這意味着你在現實中通過初始化：

BANCO_DE_DADOS = openOrCreateDatabase(null, MODE_PRIVATE, null); 

因此空指針除外離子。請檢查它是否設置了某些內容，並且這是一條有效的路徑。

編輯：

更改文件名具有正確的擴展名。 .db

private static String NOME_BANCO = "Cadastro"; 

變爲：

private static String NOME_BANCO = "Cadastro.db";