android - 将消息从 Activity 传递到 Fragment

Question

我似乎无法将 Activity 中获取的数据传递给 Fragment。数据没有出现在列表 fragment 中!这是我的列表 fragment Activity 。每次我将一个项目添加到列表中时，我都会重新实例化该 fragment ，也就是 bundle 一个项目，并使用新 fragment 中的构造函数来完成它。

package com.example.sample;

import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.widget.Toast;

import com.actionbarsherlock.app.ActionBar;
import com.actionbarsherlock.app.ActionBar.Tab;
import com.actionbarsherlock.app.SherlockFragmentActivity;
import com.actionbarsherlock.view.Menu;
import com.actionbarsherlock.view.MenuItem;

/**
 * An activity representing a list of Courses. This activity has different
 * presentations for handset and tablet-size devices. On handsets, the activity
 * presents a list of items, which when touched, lead to a
 * {@link CourseDetailActivity} representing item details. On tablets, the
 * activity presents the list of items and item details side-by-side using two
 * vertical panes.
 * <p>
 * The activity makes heavy use of fragments. The list of items is a
 * {@link CourseListFragment} and the item details (if present) is a
 * {@link CourseDetailFragment}.
 * <p>
 * This activity also implements the required
 * {@link CourseListFragment.Callbacks} interface to listen for item selections.
 */
public class CourseListActivity extends SherlockFragmentActivity implements
    CourseListFragment.Callbacks {

CourseListFragment listFrag;

public static String courseName;
private static final int REQUEST_CODE = 10;

/**
 * Whether or not the activity is in two-pane mode, i.e. running on a tablet
 * device.
 */
private boolean mTwoPane;
private boolean once = true;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_course_list);

    if (findViewById(R.id.course_detail_container) != null) {
        // The detail container view will be present only in the
        // large-screen layouts (res/values-large and
        // res/values-sw600dp). If this view is present, then the
        // activity should be in two-pane mode.
        mTwoPane = true;

        // In two-pane mode, list items should be given the
        // 'activated' state when touched.
        listFrag = ((CourseListFragment) getSupportFragmentManager().findFragmentById(
                R.id.course_list));
        listFrag.setActivateOnItemClick(true);
    }

    // TODO: If exposing deep links into your app, handle intents here.
}

/**
 * Callback method from {@link CourseListFragment.Callbacks} indicating that
 * the item with the given ID was selected.
 */

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

public boolean onOptionsItemSelected(MenuItem item) {
    boolean bool;
    switch (item.getItemId()) {
    case R.id.add_course:
        Intent intent = new Intent(this, CourseAddActivity.class);
        startActivityForResult(intent, REQUEST_CODE);
        bool = true;
    default:
        bool = super.onOptionsItemSelected(item);
    }
    return bool;
}

@Override
  protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) {
      if (data.hasExtra("courseName")) {
        courseName = data.getExtras().getString("courseName");
        Bundle args = new Bundle();
        args.putString("courseKey", courseName);
        listFrag = new CourseListFragment(args);
      }
    }
  }

@Override
public void onItemSelected(String id) {
    if (mTwoPane) {
        // In two-pane mode, show the detail view in this activity by
        // adding or replacing the detail fragment using a
        // fragment transaction.
        if (once) {
            ActionBar actionBar = getSupportActionBar();
            actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
            // initiating both tabs and set text to it.
            ActionBar.Tab assignTab = actionBar.newTab().setText(
                    "Assignments");
            ActionBar.Tab schedTab = actionBar.newTab().setText("Schedule");
            ActionBar.Tab contactTab = actionBar.newTab()
                    .setText("Contact");

            // Create three fragments to display content
            Fragment assignFragment = new Assignments();
            Fragment schedFragment = new Schedule();
            Fragment contactFragment = new Contact();

            assignTab.setTabListener(new MyTabsListener(assignFragment));
            schedTab.setTabListener(new MyTabsListener(schedFragment));
            contactTab.setTabListener(new MyTabsListener(contactFragment));

            actionBar.addTab(assignTab);
            actionBar.addTab(schedTab);
            actionBar.addTab(contactTab);
            once = false;
        }
    } else {
        // In single-pane mode, simply start the detail activity
        // for the selected item ID.
        Intent detailIntent = new Intent(this, CourseDetailActivity.class);
        startActivity(detailIntent);
    }

}

class MyTabsListener implements ActionBar.TabListener {
    public Fragment fragment;

    public MyTabsListener(Fragment fragment) {
        this.fragment = fragment;
    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
    }

    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        ft.replace(R.id.course_detail_container, fragment);
    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        ft.remove(fragment);
    }
}
}

这是我的 ListFragment，我在其中创建了两个构造函数，其中一个接受参数。

package com.example.sample;

import java.util.ArrayList;

import android.app.Activity;
import android.os.Build;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

import com.actionbarsherlock.app.SherlockListFragment;

/**
 * A list fragment representing a list of Courses. This fragment also supports
 * tablet devices by allowing list items to be given an 'activated' state upon
 * selection. This helps indicate which item is currently being viewed in a
 * {@link CourseDetailFragment}.
 * <p>
 * Activities containing this fragment MUST implement the {@link Callbacks}
 * interface.
 */
public class CourseListFragment extends SherlockListFragment {

private static String courseName;
ArrayList<String> courseItems;
ArrayAdapter<String> adapter;
/**
 * The serialization (saved instance state) Bundle key representing the
 * activated item position. Only used on tablets.
 */
private static final String STATE_ACTIVATED_POSITION = "activated_position";

/**
 * The fragment's current callback object, which is notified of list item
 * clicks.
 */
private Callbacks mCallbacks = sDummyCallbacks;

/**
 * The current activated item position. Only used on tablets.
 */
private int mActivatedPosition = ListView.INVALID_POSITION;

/**
 * A callback interface that all activities containing this fragment must
 * implement. This mechanism allows activities to be notified of item
 * selections.
 */
public interface Callbacks {
    /**
     * Callback for when an item has been selected.
     */
    public void onItemSelected(String id);
}

/**
 * A dummy implementation of the {@link Callbacks} interface that does
 * nothing. Used only when this fragment is not attached to an activity.
 */
private static Callbacks sDummyCallbacks = new Callbacks() {
    @Override
    public void onItemSelected(String id) {
    }
};

/**
 * Mandatory empty constructor for the fragment manager to instantiate the
 * fragment (e.g. upon screen orientation changes).
 */
public CourseListFragment() {
}

public CourseListFragment(Bundle args) {
    courseName = args.get("courseKey").toString();
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    courseItems = new ArrayList<String>();
    adapter = new ArrayAdapter<String>(getActivity(),
            android.R.layout.simple_list_item_1, courseItems);
    // TODO: replace with a real list adapter.
    int layout = (Build.VERSION.SDK_INT >= 11) ? android.R.layout.simple_list_item_activated_1
            : android.R.layout.simple_list_item_1;
    setListAdapter(adapter);
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    // Restore the previously serialized activated item position.
    if (savedInstanceState != null
            && savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
        setActivatedPosition(savedInstanceState
                .getInt(STATE_ACTIVATED_POSITION));
        courseItems.add(courseName);
        adapter.notifyDataSetChanged();
    }
}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);

    // Activities containing this fragment must implement its callbacks.
    if (!(activity instanceof Callbacks)) {
        throw new IllegalStateException(
                "Activity must implement fragment's callbacks.");
    }

    mCallbacks = (Callbacks) activity;
}

@Override
public void onDetach() {
    super.onDetach();

    // Reset the active callbacks interface to the dummy implementation.
    mCallbacks = sDummyCallbacks;
}

@Override
public void onListItemClick(ListView listView, View view, int position,
        long id) {
    super.onListItemClick(listView, view, position, id);

    // Notify the active callbacks interface (the activity, if the
    // fragment is attached to one) that an item has been selected.
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    if (mActivatedPosition != ListView.INVALID_POSITION) {
        // Serialize and persist the activated item position.
        outState.putInt(STATE_ACTIVATED_POSITION, mActivatedPosition);
    }
}

/**
 * Turns on activate-on-click mode. When this mode is on, list items will be
 * given the 'activated' state when touched.
 */
public void setActivateOnItemClick(boolean activateOnItemClick) {
    // When setting CHOICE_MODE_SINGLE, ListView will automatically
    // give items the 'activated' state when touched.
    getListView().setChoiceMode(
            activateOnItemClick ? ListView.CHOICE_MODE_SINGLE
                    : ListView.CHOICE_MODE_NONE);
}

private void setActivatedPosition(int position) {
    if (position == ListView.INVALID_POSITION) {
        getListView().setItemChecked(mActivatedPosition, false);
    } else {
        getListView().setItemChecked(position, true);
    }

    mActivatedPosition = position;
}
}

非常感谢任何帮助!谢谢!

Answer 1

如果这样重新实例化，CourseListFragment的类变量会在每次调用时被销毁

listFrag = new CourseListFragment(args);

您应该在 CourseListFragment 中创建一个方法来添加类(class)名称而不破坏当前 fragment :

public void addCourse(String courseName) {
    courseItems.add(courseName);
    adapter.notifyDataSetChanged();
}

在你的 Activity 中:

@Override
  protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) {
      if (data.hasExtra("courseName")) {
        courseName = data.getExtras().getString("courseName");
        listFrag.addCourse(courseName);
      }
    }
  }