Question

所以我一直在Android Studio中处理这个Android项目，我让用户创建待办事项列表。这是课堂作业，我必须与单身人士合作。我一直在阅读很多关于它的信息和问题/答案，但这只会让我越来越困惑。

在我的MainActivity我尝试调用方法ReadTitlesFromFile，但我收到错误：

修改者＆＃39; public＆＃39;不允许在这里

和

内部类不能有静态声明

即使代码与我在某处找到的示例完全相同。有人可以帮我解决错误吗？

这是我的单身人士：

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();
    }
}

}

这是MainActivity类：

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);
        }
    }

}

我很抱歉，如果这是一个愚蠢的问题，或者之前已经被问过，但我是编程的新手，所有的信息都会让我感到困惑。

Answer 1

您已在类中放置了一个类。这就是您收到错误的原因："Modifier 'public' not allowed here"

无论如何你不需要班级ReadTitles;即使您使用它，也请从static方法中删除main修饰符。

简单地说，而不是：

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

把这个：

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

Answer 2

如前所述，您试图在ReadTitles方法中声明类型为onCreate的类。你不能这样做。

而不是：

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

您只需在onCreate内调用您的单身人士实例即可。但是，您需要先获取应用Context，然后才能调用ReadTitlesFromFile方法。目前，您在将参数传递给ReadTitlesFromFile时尝试显式声明类型。你不这样做，因为它会导致编译器错误。而是使用getApplicationContext()方法获取Context。见下文：

@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);
}

在活动中使用Singleton方法（Android）

2 个答案: