参数 UserFragment 无法转换为 Fragment

Question

我在我的 android studio 项目中发现了错误。我尝试将 SQLite 添加到我的片段中。这是错误。

错误：(75, 25) 错误：MainMenu 类中的方法 updateDisplay 不能应用于给定类型； 必需：片段 找到：用户片段 原因：实参UserFragment无法通过方法调用转换为Fragment

MainMenu.Java

public class MainMenu extends ActionBarActivity {

private DrawerLayout mDrawerLayout;
private NavigationView navigationView;

String address = null;
private ProgressDialog progress;
BluetoothAdapter myBluetooth = null;
BluetoothSocket btSocket = null;
private boolean isBtConnected = false;
//SPP UUID. Look for it
static final UUID myUUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");

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

    Intent newint = getIntent();
    address = newint.getStringExtra(DeviceList.EXTRA_ADDRESS);

    new ConnectBT().execute();

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    ActionBar actionBar = getSupportActionBar();
    actionBar.setHomeAsUpIndicator(R.drawable.ic_menu);
    actionBar.setDisplayHomeAsUpEnabled(true);

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    navigationView = (NavigationView) findViewById(R.id.navigation_view);

    navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(MenuItem menuItem) {
            menuItem.setChecked(true);
            mDrawerLayout.closeDrawers();

            switch (menuItem.getItemId()) {

                case R.id.navigation_item_notification:
                    updateDisplay(new NotificationFragment());
                    break;

                case R.id.navigation_item_user:
                    updateDisplay(new UserFragment());
                    break;

                case R.id.navigation_item_log:
                    updateDisplay(new LogFragment());
                    break;

                case R.id.navigation_sub_item_01:
                    updateDisplay(new AboutFragment());
                    break;

                case R.id.navigation_sub_item_02:
                {
                    if (btSocket!=null) //If the btSocket is busy
                    {
                        try
                        {
                            btSocket.close(); //close connection
                        }
                        catch (IOException e)
                        { msg("Error");}
                    }
                    finish(); //return to the first layout

                }
            }
            return true;
        }
    });

}

private void updateDisplay(Fragment fragment) {

    FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.beginTransaction().replace(R.id.frame_container, fragment).commit();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    switch (id) {
        case android.R.id.home:
            mDrawerLayout.openDrawer(GravityCompat.START);
            return true;
        case R.id.action_settings:
            return true;

    }

    return super.onOptionsItemSelected(item);
}

private void Disconnect()
{
    if (btSocket!=null) //If the btSocket is busy
    {
        try
        {
            btSocket.close(); //close connection
        }
        catch (IOException e)
        { msg("Error");}
    }
    finish(); //return to the first layout

}

// fast way to call Toast
private void msg(String s)
{
    Toast.makeText(getApplicationContext(),s,Toast.LENGTH_LONG).show();
}

private class ConnectBT extends AsyncTask<Void, Void, Void>  // UI thread
{
    private boolean ConnectSuccess = true; //if it's here, it's almost connected

    @Override
    protected void onPreExecute()
    {
        progress = ProgressDialog.show(MainMenu.this, "Connecting...", "Please wait!!!");  //show a progress dialog
    }

    @Override
    protected Void doInBackground(Void... devices) //while the progress dialog is shown, the connection is done in background
    {
        try
        {
            if (btSocket == null || !isBtConnected)
            {
             myBluetooth = BluetoothAdapter.getDefaultAdapter();//get the mobile bluetooth device
             BluetoothDevice dispositivo = myBluetooth.getRemoteDevice(address);//connects to the device's address and checks if it's available
             btSocket = dispositivo.createInsecureRfcommSocketToServiceRecord(myUUID);//create a RFCOMM (SPP) connection
             BluetoothAdapter.getDefaultAdapter().cancelDiscovery();
             btSocket.connect();//start connection
            }
        }
        catch (IOException e)
        {
            ConnectSuccess = false;//if the try failed, you can check the exception here
        }
        return null;
    }
    @Override
    protected void onPostExecute(Void result) //after the doInBackground, it checks if everything went fine
    {
        super.onPostExecute(result);

        if (!ConnectSuccess)
        {
            msg("Connection Failed. Is it a SPP Bluetooth? Try again.");
            finish();
        }
        else
        {
            msg("Connected.");
            isBtConnected = true;
        }
        progress.dismiss();
    }
}

UserFragment.Java

public class UserFragment extends ActionBarActivity {

private DBManager dbManager;

private ListView listView;

private SimpleCursorAdapter adapter;

final String[] from = new String[]{DatabaseHelper._ID,
        DatabaseHelper.SUBJECT, DatabaseHelper.DESC};

final int[] to = new int[]{R.id.id, R.id.title, R.id.desc};

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

    setContentView(R.layout.user_fragment);

    dbManager = new DBManager(this);
    dbManager.open();
    Cursor cursor = dbManager.fetch();

    listView = (ListView) findViewById(R.id.list_view);
    listView.setEmptyView(findViewById(R.id.empty));

    adapter = new SimpleCursorAdapter(this, R.layout.activity_view_record, cursor, from, to, 0);
    adapter.notifyDataSetChanged();

    listView.setAdapter(adapter);

    // OnCLickListiner For List Items
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long viewId) {
            TextView idTextView = (TextView) view.findViewById(R.id.id);
            TextView titleTextView = (TextView) view.findViewById(R.id.title);
            TextView descTextView = (TextView) view.findViewById(R.id.desc);

            String id = idTextView.getText().toString();
            String title = titleTextView.getText().toString();
            String desc = descTextView.getText().toString();

            Intent modify_intent = new Intent(getApplicationContext(), ModifyCountryActivity.class);
            modify_intent.putExtra("title", title);
            modify_intent.putExtra("desc", desc);
            modify_intent.putExtra("id", id);

            startActivity(modify_intent);
        }
    });
}

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

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    int id = item.getItemId();
    if (id == R.id.add_record) {

        Intent add_mem = new Intent(this, AddCountryActivity.class);
        startActivity(add_mem);

    }
    return super.onOptionsItemSelected(item);
}

如果我在 UserFragment 上使用 Fragment，我在 UserFragment 上出现错误。但是，如果我在 UserFragment 上使用 ActionBarActivity，我在 MainMenu 上出现错误。有人可以帮助我吗？我的代码有什么问题？

Answer 1

您的 UserFragment 不是 Fragment，而是 Activity 的实例，因为您正在扩展 ActionBarActivity。

Answer 2

将 userfragment 更改为 fragment 而不是 actionbaractivity ，并告诉我您遇到的错误是什么

Answer 3

UserFragment 需要继承 Fragment 并且需要实现 onCreateView 方法：

public class UserFragment extends Fragment {

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View fView = inflater.inflate(R.id.your_layour, container, false);

    TextView someTextView = (TextView) fView.findViewById(R.id.your_text_view);

    return fView;

}

}

Answer 4

问题依赖于您提供给updateDisplay() 方法的cast and the parametrization。 当涉及到时，以下错误很明显：

找到的片段：UserFragment 原因：实际参数 UserFragment 无法通过方法调用转换为Fragment

基本上，在您正在调用的 NavigationItemSelected() 方法中：

case R.id.navigation_item_user:
    updateDisplay(new UserFragment());
    break;

并将 Activity 作为参数传递（您的 UserFragment 扩展了作为 Activity 的 ActionBarActivity）。
但是这个方法应该被赋予一个Fragment，因此在

中的转换错误

private void updateDisplay(Fragment fragment) {
    FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.beginTransaction().replace(R.id.frame_container, fragment).commit();
}

为了解决这个问题，您必须确保您的 UserFragment 扩展了 Fragment 而不是 Activity，否则您将无法将其传递到 FragmentManager 事务

应该是这样的（或多或少。一定要检查细节）：

public class UserFragment extends Fragment {

private DBManager dbManager;
private ListView listView;
private SimpleCursorAdapter adapter;

final String[] from = new String[]{DatabaseHelper._ID, DatabaseHelper.SUBJECT, DatabaseHelper.DESC};
final int[] to = new int[]{R.id.id, R.id.title, R.id.desc};

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.user_fragment,container, false);
    return view;
}


@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    dbManager = new DBManager(this);
    dbManager.open();
    Cursor cursor = dbManager.fetch();

    listView = (ListView) findViewById(R.id.list_view);
    listView.setEmptyView(findViewById(R.id.empty));

    adapter = new SimpleCursorAdapter(this, R.layout.activity_view_record, cursor, from, to, 0);
    adapter.notifyDataSetChanged();

    listView.setAdapter(adapter);

    // OnCLickListiner For List Items
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long viewId) {
            TextView idTextView = (TextView) view.findViewById(R.id.id);
            TextView titleTextView = (TextView) view.findViewById(R.id.title);
            TextView descTextView = (TextView) view.findViewById(R.id.desc);

            String id = idTextView.getText().toString();
            String title = titleTextView.getText().toString();
            String desc = descTextView.getText().toString();

            Intent modify_intent = new Intent(getApplicationContext(), ModifyCountryActivity.class);
            modify_intent.putExtra("title", title);
            modify_intent.putExtra("desc", desc);
            modify_intent.putExtra("id", id);

            startActivity(modify_intent);
        }
    });
}

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

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    int id = item.getItemId();
    if (id == R.id.add_record) {

        Intent add_mem = new Intent(this, AddCountryActivity.class);
        startActivity(add_mem);

    }
    return super.onOptionsItemSelected(item);
}

问候，