在活動中使用Singleton方法（Android）

Question

所以我一直在Android Studio中處理這個Android項目，我讓用戶創建待辦事項列表。這是一個班級任務，我必須與單身人士合作。我一直在閱讀大量關於它的信息和問題/答案，但這隻會讓我越來越困惑。

在我MainActivity我試圖調用該方法ReadTitlesFromFile，但我得到的錯誤：

Modifier 'public' not allowed here

和

Inner classes cannot have static declarations

即使代碼是完全一樣的，我發現的例子某處。有人可以幫我解決這個錯誤嗎？

這是我的單身：

public class ToDoManagerSingleton { 
private ArrayList<ToDoList> listTitles; 

// One single instance for the entire app 
private static ToDoManagerSingleton ourInstance = new ToDoManagerSingleton(); 

// Constructor 
private ToDoManagerSingleton() { 
    // Empty ArrayList with in it the different lists 
    listTitles = new ArrayList<ToDoList>(); 
} 

// Method to get the one single instance 
public static ToDoManagerSingleton getInstance() { 
    return ourInstance; 
} 

// Getter and setter 
public void setListTitles (ArrayList listTitlesArg){ 
    listTitles = listTitlesArg; 
} 

public ArrayList getListTitles(){ 
    return listTitles; 
} 

// Add new title to list 
public void AddNewTitle(ToDoList title){ 
    listTitles.add(title); 
} 

// Write list titles to a file 
public void WriteListTitlesToFile (Context context){ 
    PrintStream outstream = null; 
    try{ 
     outstream = new PrintStream(context.openFileOutput("titlesfile.txt", Context.MODE_PRIVATE)); 
     for (ToDoList listTitle : listTitles) { 
      outstream.println(listTitle); 
     } 
    } 
    catch (FileNotFoundException e){ 
     e.printStackTrace(); 
    } 
} 

// Read titlesfile.txt 
public void ReadTitlesFromFile(Context context){ 
    try { 
     FileInputStream inStream = context.openFileInput("titlesfile.txt"); 
     InputStreamReader inReader = new InputStreamReader(inStream); 
     BufferedReader bufferedReader = new BufferedReader(inReader); 
     StringBuilder sBuilder = new StringBuilder(); 
     String line; 
     while ((line = bufferedReader.readLine()) != null){ 
      sBuilder.append(line).append("\n"); 
     } 
    } 
    catch (FileNotFoundException e){ 
     e.printStackTrace(); 
    } 
    catch (IOException e){ 
     e.printStackTrace(); 
    } 
} 

// Read itemsfile.txt 
public void ReadItemsFromFile(Context context){ 
    try { 
     FileInputStream inStream = context.openFileInput("itemsfile.txt"); 
     InputStreamReader inReader = new InputStreamReader(inStream); 
     BufferedReader bufferedReader = new BufferedReader(inReader); 
     StringBuilder sBuilder = new StringBuilder(); 
     String line; 
     while ((line = bufferedReader.readLine()) != null){ 
      sBuilder.append(line).append("\n"); 
     } 
    } 
    catch (FileNotFoundException e){ 
     e.printStackTrace(); 
    } 
    catch (IOException e){ 
     e.printStackTrace(); 
    } 
} 

}

這是MainActivity類：

public class MainActivity extends AppCompatActivity { 

ListView showSavedFilesListview; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    // Initialize listview 
    showSavedFilesListview = (ListView) findViewById(R.id.ListView1); 

    // Read titles from titlesfile.txt 
    public class ReadTitles { 
     public static void main (Context context) { 
      ToDoManagerSingleton tmp = ToDoManagerSingleton.getInstance(); 
      tmp.ReadTitlesFromFile(Context context); 
     } 
    } 

} 

對不起，如果這是一個愚蠢的問題，或者如果它有之前已經被問過了，但我是編程新手，所有的信息都會讓我困惑。

Answer 1

您已經在方法中放置了一個類。這就是爲什麼你得到的錯誤："Modifier 'public' not allowed here"

反正你不需要類ReadTitles;即使您使用它，也可以從main方法中刪除static修飾符。

簡單，而不是這樣的：

// Read titles from titlesfile.txt 
public class ReadTitles { 
    public static void main (Context context) { 
     ToDoManagerSingleton tmp = ToDoManagerSingleton.getInstance(); 
     tmp.ReadTitlesFromFile(Context context); 
    } 
} 

把這個：

// Read titles from titlesfile.txt 
ToDoManagerSingleton tmp = ToDoManagerSingleton.getInstance(); 
tmp.ReadTitlesFromFile(this); // use the Activity context 

Answer 2

正如前面提到的，你試圖將onCreate方法中聲明一個類ReadTitles類型。你不可以做這個。

相反的：

public class ReadTitles { 
    public static void main (Context context) { 
     ToDoManagerSingleton tmp = ToDoManagerSingleton.getInstance(); 
     tmp.ReadTitlesFromFile(Context context); 
    } 
} 

你可以簡單地內onCreate打電話給你的單身實例。但是，您需要先獲得應用程序Context，然後才能致電ReadTitlesFromFile方法。目前，您正試圖在將參數傳遞給ReadTitlesFromFile時明確聲明類型。你不這樣做，因爲它會導致編譯器錯誤。相反，使用getApplicationContext()方法獲得Context。看到下面：

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    // Initialize listview 
    showSavedFilesListview = (ListView) findViewById(R.id.ListView1); 

    // Read titles from titlesfile.txt 
    ToDoManagerSingleton tmp = ToDoManagerSingleton.getInstance(); 
    Context context = getApplicationContext(); 
    tmp.ReadTitlesFromFile(context); 
}