Android Studio，Sql，TextView

Question

我按照我的first answered post發佈。

經過測試並添加了建議的修改後，我仍然無法讓我的代碼正常工作。每次我重新開始tuto，然後嘗試添加我的代碼，然後失敗。

如果你能改正我或指出我錯過了這一點，那將會很棒。

這工作得很好：

在MyActivity.java有一個可點擊按鈕

/** Called when the user clicks the Send button */ 
public void goExample(View view) { 
    Intent intent = new Intent(this, Example.class); 
    startActivity(intent); 
} 

這使類實例：

public class Example extends Activity { 

     @Override 
     public void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      TextView total = (TextView)findViewById(R.id.total); 
      setContentView(R.layout.example); 
     } 

     @Override 
     public boolean onCreateOptionsMenu(Menu menu) { 
      getMenuInflater().inflate(R.menu.menu, menu); 
      return true; 
     }} 

隨着其觀點的example.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    tools:context=".Example"> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:id="@+android:id/total" 
     android:layout_weight="1" /> 

</RelativeLayout> 

沒有問題，直到我嘗試添加自己的代碼（如下）：

public class Example extends MyActivity { 

    private TaskDBHelper helper; 

    public int getContactsCount() { 
     helper = new TaskDBHelper(Example.this); 
     SQLiteDatabase db = helper.getReadableDatabase(); 
     String countQuery = "SELECT * FROM " + Playas.TABLE; 
     Cursor cursor = db.rawQuery(countQuery, null); 
     return cursor.getCount(); 
    } 

    public static void main(String[] args) { 
     Example example = new Example(); 
     int a = example.getContactsCount(); 
     System.out.println(a); 
    } 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     TextView total = (TextView)findViewById(R.id.total); 
     total.setText(String.valueOf(getContactsCount())); 
     setContentView(R.layout.example); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     getMenuInflater().inflate(R.menu.menu, menu); 
     return true; 
    } 
} 

然後悲慘的失敗，與以下錯誤：

6715-6715/tab.sqltesting.com.myapplication E/AndroidRuntime﹕ FATAL EXCEPTION: main 
    java.lang.RuntimeException: Unable to start activity ComponentInfo{tab.sqltesting.com.myapplication/tab.sqltesting.com.myapplication.Example}: java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteQuery: SELECT * FROM joueurs 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097) 
      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2122) 
      at android.app.ActivityThread.access$600(ActivityThread.java:140) 
      at dalvik.system.NativeStart.main(Native Method) 
... 
    Caused by: java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteQuery: SELECT * FROM joueurs 
      at android.database.sqlite.SQLiteClosable.acquireReference(SQLiteClosable.java:55) 
      at android.database.sqlite.SQLiteQuery.fillWindow(SQLiteQuery.java:58) 

老實說，我不知道做什麼，任何幫助將不勝感激......

感謝

Answer 1

在您的類示例中。你應該在setcontentview（）之後聲明小部件;

public class Example extends Activity { 

     @Override 
     public void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.example); 
      TextView total = (TextView)findViewById(R.id.total); 
     } 

     @Override 
     public boolean onCreateOptionsMenu(Menu menu) { 
      getMenuInflater().inflate(R.menu.menu, menu); 
      return true; 
     }} 

Answer 2

你爲什麼不反向遊兩行代碼。

，而不是這樣的：

@Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     TextView total = (TextView)findViewById(R.id.total); 
     setContentView(R.layout.example); 
    } 

做這樣的：

@Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     setContentView(R.layout.example); 
     TextView total = (TextView)findViewById(R.id.total); 
    } 

提示：您應該先設置你的內容視圖，然後聲明變量。