片段之间的ClassCastException.Communicate

Question

我想把一个字符串从一个片段传递给另一个片段。我做了下一步

1)创建接口

public interface Communicator {
public void respond(String data); }

2)在BakeFragment(我传递变量的片段)中，我创建了

public class BakeFragment extends Fragment {... 
Communicator mCallBack;

然后在警报对话框中传递myString ...

builder.setNegativeButton("Заказать", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {

                    orderList.add(myString);
                    mCallBack.respond(myString);
                  Toast.makeText(getActivity(), "Вы выбрали "+myString, Toast.LENGTH_LONG).show();
                    dialog.cancel();
                }
            }); 
@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    mCallBack = (Communicator) getActivity();
}  ...}

3)我在MainActivity中得到这个字符串

public class MainActivity extends AppCompatActivity implements Communicator{  ... 
 @Override
public void respond(String data) {
    FragmentManager manager = getFragmentManager();
    OrderFragment f2 =(OrderFragment)manager.findFragmentById(R.id.frame_container);
    f2.changeData(data);
}   ....}

4)然后我从MainActivity获取字符串并传递给OrderFragment

public class OrderFragment extends Fragment {...
public void changeData(String data){
         finalOrderList.add(data);

 } ...}

​

​

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1)我添加了一个项目。2)当我添加一个项目时，我会得到这个列表(Screen2) 3)当我转到orderlist时，它是空的

MainActivity

public class MainActivity extends AppCompatActivity implements Communicator{
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;

// nav drawer title
private CharSequence mDrawerTitle;

// used to store app title
private CharSequence mTitle;

// slide menu items
private String[] navMenuTitles;
private TypedArray navMenuIcons;

private ArrayList<NavDrawerItem> navDrawerItems;
private NavDrawerListAdapter adapter;

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



    mTitle = mDrawerTitle = getTitle();

    // load slide menu items
    navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);

    // nav drawer icons from resources
    navMenuIcons = getResources()
            .obtainTypedArray(R.array.nav_drawer_icons);

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerList = (ListView) findViewById(R.id.list_slidermenu);

    navDrawerItems = new ArrayList<NavDrawerItem>();



    // adding nav drawer items to array
    // Home
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
    // Find People
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
    // Photos
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
    // Communities, Will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1)));
    // Pages
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], navMenuIcons.getResourceId(4, -1)));
    // What's hot, We  will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], navMenuIcons.getResourceId(5, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[6], navMenuIcons.getResourceId(6, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[7], navMenuIcons.getResourceId(7, -1)));
    // Find People
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[8], navMenuIcons.getResourceId(8, -1)));
    // Photos
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[9], navMenuIcons.getResourceId(9, -1)));
    // Communities, Will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[10], navMenuIcons.getResourceId(10, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[11], navMenuIcons.getResourceId(11, -1)));


    // Recycle the typed array
    navMenuIcons.recycle();

    mDrawerList.setOnItemClickListener(new SlideMenuClickListener());

    // setting the nav drawer list adapter
    adapter = new NavDrawerListAdapter(getApplicationContext(),
            navDrawerItems);
    mDrawerList.setAdapter(adapter);

    // enabling action bar app icon and behaving it as toggle button
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setHomeButtonEnabled(true);

    mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, R.string.navigation_drawer_open, R.string.navigation_drawer_close) {
        public void onDrawerClosed(View view) {
            getSupportActionBar().setTitle(mTitle);
            // calling onPrepareOptionsMenu() to show action bar icons
            invalidateOptionsMenu();

        }

        public void onDrawerOpened(View drawerView) {
            getSupportActionBar().setTitle(mDrawerTitle);
            // calling onPrepareOptionsMenu() to hide action bar icons
            invalidateOptionsMenu();
        }
    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);

    if (savedInstanceState == null) {


        displayView(11);
    }

}

@Override
public void respond(String data) {
    for(int i = getSupportFragmentManager().getBackStackEntryCount() -1; i >= 0; i--) {
        String tag = getSupportFragmentManager().getBackStackEntryAt(i).getName();
        OrderFragment fragment;
        fragment=(OrderFragment)getFragmentManager().findFragmentByTag(tag);
        FragmentManager manager = getFragmentManager();
        manager.beginTransaction().replace(R.id.frame_container, fragment).commit();
        if(fragment instanceof OrderFragment) {
            fragment.changeData(data);
            break;
        }

    }


}


/**
 * Slide menu item click listener
 */
private class SlideMenuClickListener implements
        ListView.OnItemClickListener {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
                            long id) {
        // display view for selected nav drawer item
        displayView(position);
    }
}

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

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // toggle nav drawer on selecting action bar app icon/title
    if (mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    }
    // Handle action bar actions click
    switch (item.getItemId()) {
        case R.id.action_settings:
          return true;
        default:
          displayView(11);

            //Toast.makeText(getApplicationContext(), "RasRas", Toast.LENGTH_LONG).show();
            return true;
    }
}

/* *
 * Called when invalidateOptionsMenu() is triggered
 */
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    // if nav drawer is opened, hide the action items
    boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
    menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
    return super.onPrepareOptionsMenu(menu);
}

/**
 * Diplaying fragment view for selected nav drawer list item
 */
private void displayView(int position) {
    // update the main content by replacing fragments
    Fragment fragment = null;
    switch (position) {
        case 0:
            fragment = new BakeFragment();
            break;
        case 1:
            fragment = new GarnishFragment();
            break;
        case 2:
            fragment = new HotDishesFragment();
            break;
        case 3:
            fragment = new DesertsFragment();
            break;
        case 4:
            fragment = new HomeFragment();
            break;
        case 5:
            fragment = new SnacksFragment();
            break;
        case 6:
            fragment = new DrinkFragment();
            break;
        case 7:
            fragment = new PizzaFragment();
            break;
        case 8:
            fragment = new SaladFragment();
            break;
        case 9:
            fragment = new ConfectionFragment();
            break;
        case 10:
            fragment = new SoupFragment();
            break;
        case 11:
            fragment = new OrderFragment();
        default:
            break;
    }

    if (fragment != null) {
        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.frame_container, fragment).commit();

        // update selected item and title, then close the drawer
        mDrawerList.setItemChecked(position, true);
        mDrawerList.setSelection(position);
        setTitle(navMenuTitles[position]);
        mDrawerLayout.closeDrawer(mDrawerList);
    } else {
        // error in creating fragment
        Log.e("MainActivity", "Error in creating fragment");
    }
}

@Override
public void setTitle(CharSequence title) {
    mTitle = title;
    getSupportActionBar().setTitle(mTitle);
}

/**
 * When using the ActionBarDrawerToggle, you must call it during
 * onPostCreate() and onConfigurationChanged()...
 */

@Override
protected void onPostCreate(Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);
    // Sync the toggle state after onRestoreInstanceState has occurred.
    mDrawerToggle.syncState();
}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    // Pass any configuration change to the drawer toggls
    mDrawerToggle.onConfigurationChanged(newConfig);
}}

Answer 1

日志说明了一切。您正在将BakeFragment类型强制转换为OrderFragment。我建议根据您作为param获得的字符串数据来标识片段类型：

@Override
public void respond(String data) {
    FragmentManager manager = getFragmentManager();
    if( <CheckdataForFragmentType> )
    {
        // if data maps to OrderFragment type
        OrderFragment f2 =(OrderFragment)manager.findFragmentById(R.id.frame_container);
        f2.changeData(data);
    }
}

Answer 2

我假设您已经将OrderFragment和BakeFragment添加到frame_container容器中。因此，为了避免ClassCastException，请使用以下代码：

for(int i = getSupportFragmentManager().getBackStackEntryCount() -1; i >= 0; i--) { String tag = getSupportFragmentManager().getBackStackEntryAt(i).getName(); Fragment fragment = getSupportFragmentManager().findFragmentByTag(tag); if(fragment instanceof OrderFragment) { f2.changeData(data); break; } }

注意:在通过调用getSupportFragmentManager().beginTransaction() .add(R.id.frame_container , mFragment, "bakefragment").addToBackStack("bakefragment").commit();将片段添加到Activity时，您需要将标签设置为fragmnet