如何在横向中并排显示2个片段

Question

我有一个 Activity1 托管 ListFragmentA。
单击列表中的一个项目时，我会启动托管 ListFragmentB 的 Activity2。
无论是纵向还是横向，我都会一次看到 1 个列表。
当我处于横向模式（或者我猜是在平板电脑中）时，我有兴趣查看这两个片段。
IE。显示屏左侧的ListFragmentA 和右侧的ListFragmentB。这样当用户按下ListFragmentA 中的项目时，ListFragmentB 中的正确数据就会显示出来。
这是怎么做到的？在我看来，横向模式下的布局似乎很乏味/错误，老实说，我不确定它是如何完成的。
有没有我可以研究的好例子？

Answer 1

纵向模式的fragment_layout.xml是：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <fragment
        android:id="@+id/titles"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        class="edu.dartmouth.cs.FragmentLayout$TitlesFragment" />

</FrameLayout>

在横向模式下，单个活动 (FragmentLayout) 处理两个片段。我们还将考虑以编程方式插入片段。考虑景观 res/layout-land/fragment_layout。

横屏模式的fragment_layout.xml是：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:baselineAligned="false"
    android:orientation="horizontal" >

    <fragment
        android:id="@+id/titles"
        android:layout_width="0px"
        android:layout_height="match_parent"
        android:layout_weight="1"
        class="edu.dartmouth.cs.FragmentLayout$TitlesFragment" />

    <FrameLayout
        android:id="@+id/details"
        android:layout_width="0px"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:background="?android:attr/detailsElementBackground" />

</LinearLayout>

如果您在 TitlesFragment: onActivityCreated() 中注释掉下面显示的代码行（当 FragmentLayout onCreate() 返回时调用），那么您将在上面的 frame_layout 中看到加载时的空白。如果没有重新添加该行，则在用户从列表中选择一个项目之前，不会将 DetailsFragment 加载到其中 - 此时会创建 DetailsFragment 并将其放入 FrameLayout。

 public void onActivityCreated(Bundle savedInstanceState) {
                                    super.onActivityCreated(savedInstanceState);

                                    **snippet**

                                    if (mDualPane) {
                                                // In dual-pane mode, the list view highlights the selected item.
                                                getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);
                                                // Make sure our UI is in the correct state.
                        showDetails(mCurCheckPosition);
                                    } else {

FragmentLayout（主要活动）在 onCreate() 期间以通常的方式应用布局：

public class FragmentLayout extends Activity {

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

                        // root view inflated
                        setContentView(R.layout.fragment_layout);
            }

当用户单击 ListFragment 中的一个项目时，会调用 onListItemClick() 回调，然后调用 showDetails(position) 来启动

 @Override
        public void onListItemClick(ListView l, View v, int position, long id) {

            Toast.makeText(getActivity(),
                    "onListItemClick position is" + position, Toast.LENGTH_LONG)
                    .show();

            showDetails(position);
        }

标题片段

片段使用辅助函数来显示所选项目的详细信息。

 public static class TitlesFragment extends ListFragment {
        boolean mDualPane;
        int mCurCheckPosition = 0;

        // onActivityCreated() is called when the activity's onCreate() method
        // has returned.

        @Override
        public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);

            // You can use getActivity(), which returns the activity associated
            // with a fragment.
            // The activity is a context (since Activity extends Context) .

            Toast.makeText(getActivity(), "TitlesFragment:onActivityCreated",
                    Toast.LENGTH_LONG).show();

            // Populate list with our static array of titles in list in the
            // Shakespeare class
            setListAdapter(new ArrayAdapter<String>(getActivity(),
                    android.R.layout.simple_list_item_activated_1,
                    Shakespeare.TITLES));

            // Check to see if we have a frame in which to embed the details
            // fragment directly in the containing UI.
            // R.id.details relates to the res/layout-land/fragment_layout.xml
            // This is first created when the phone is switched to landscape
            // mode

            View detailsFrame = getActivity().findViewById(R.id.details);

            Toast.makeText(getActivity(), "detailsFrame " + detailsFrame,
                    Toast.LENGTH_LONG).show();

            // Check that a view exists and is visible
            // A view is visible (0) on the screen; the default value.
            // It can also be invisible and hidden, as if the view had not been
            // added.
            //
            mDualPane = detailsFrame != null
                    && detailsFrame.getVisibility() == View.VISIBLE;

            Toast.makeText(getActivity(), "mDualPane " + mDualPane,
                    Toast.LENGTH_LONG).show();

            if (savedInstanceState != null) {
                // Restore last state for checked position.
                mCurCheckPosition = savedInstanceState.getInt("curChoice", 0);
            }

            if (mDualPane) {
                // In dual-pane mode, the list view highlights the selected
                // item.
                getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);
                // Make sure our UI is in the correct state.
                showDetails(mCurCheckPosition);
            } else {
                // We also highlight in uni-pane just for fun
                getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);
                getListView().setItemChecked(mCurCheckPosition, true);
            }
        }

管理方向翻转之间的状态 该应用程序会跟踪当前选中的选择，因此当它恢复它时 - 再次以横向方式将其作为片段生命周期中使用 onSaveInstanceState() 突出显示的最后一个位置。片段保存其当前的动态状态，因此稍后可以在重新启动其进程的新实例中重建它。如果稍后需要创建片段的新实例，那么您在此处放置在 Bundle 中的数据将在提供给 onCreate(Bundle)、onCreateView(LayoutInflater, ViewGroup, Bundle) 和 onActivityCreated(Bundle) 的 Bundle 中可用。在代码中，新片段恢复 onActivityCreated() 中的状态。这里的状态只是 mCurCheckPosition。

 @Override
        public void onSaveInstanceState(Bundle outState) {
            super.onSaveInstanceState(outState);
            Toast.makeText(getActivity(), "onSaveInstanceState",
                    Toast.LENGTH_LONG).show();

            outState.putInt("curChoice", mCurCheckPosition);
        }

FragmentManager 和 Fragment 事务

帮助函数 (showDetails(position)) 显示所选项目的详细信息，方法是在当前 UI 中就地显示片段，或启动显示片段的全新活动。

 void showDetails(int index) {
            mCurCheckPosition = index;

            // The basic design is mutli-pane (landscape on the phone) allows us
            // to display both fragments (titles and details) with in the same
            // activity; that is FragmentLayout -- one activity with two
            // fragments.
            // Else, it's single-pane (portrait on the phone) and we fire
            // another activity to render the details fragment - two activities
            // each with its own fragment .
            //
            if (mDualPane) {
                // We can display everything in-place with fragments, so update
                // the list to highlight the selected item and show the data.
                // We keep highlighted the current selection
                getListView().setItemChecked(index, true);

                // Check what fragment is currently shown, replace if needed.
                DetailsFragment details = (DetailsFragment) getFragmentManager()
                        .findFragmentById(R.id.details);
                if (details == null || details.getShownIndex() != index) {
                    // Make new fragment to show this selection.

                    details = DetailsFragment.newInstance(index);

                    Toast.makeText(getActivity(),
                            "showDetails dual-pane: create and replace fragment",
                            Toast.LENGTH_LONG).show();

                    // Execute a transaction, replacing any existing fragment
                    // with this one inside the frame.
                    FragmentTransaction ft = getFragmentManager()
                            .beginTransaction();
                    ft.replace(R.id.details, details);
                    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
                    ft.commit();
                }

            } else {
                // Otherwise we need to launch a new activity to display
                // the dialog fragment with selected text.
                // That is: if this is a single-pane (e.g., portrait mode on a
                // phone) then fire DetailsActivity to display the details
                // fragment

                // Create an intent for starting the DetailsActivity
                Intent intent = new Intent();

                // explicitly set the activity context and class
                // associated with the intent (context, class)
                intent.setClass(getActivity(), DetailsActivity.class);

                // pass the current position
                intent.putExtra("index", index);

                startActivity(intent);
            }
        }

DetailsActivity：纵向模式处理

如前所述，如果用户单击列表项并且当前布局不包括 R.id.details 视图（DetailsFragment 执行此操作），则应用程序启动 DetailsActivity 活动以显示该项目的内容。辅助函数在横向创建一个新的片段以在纵向绘制细节启动一个活动（DetailsActivity）来管理细节片段 - 即创建一个新的DetailsFragment并使用FragmentManager将其添加到根视图，如下所示。 DetailsActivity 嵌入 DetailsFragment 以在屏幕为纵向时显示选定的播放摘要：

// 这是一个辅助活动，用于显示用户在 // 屏幕不够大，无法在一个活动中全部显示。

公共静态类 DetailsActivity 扩展 Activity {

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

    Toast.makeText(this, "DetailsActivity", Toast.LENGTH_SHORT).show();

    if (getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE) {
        // If the screen is now in landscape mode, we can show the
        // dialog in-line with the list so we don't need this activity.
        finish();
        return;
    }

    if (savedInstanceState == null) {
        // During initial setup, plug in the details fragment.

        // create fragment
        DetailsFragment details = new DetailsFragment();

        // get and set the position input by user (i.e., "index")
        // which is the construction arguments for this fragment
        details.setArguments(getIntent().getExtras());

        //
        getFragmentManager().beginTransaction()
                .add(android.R.id.content, details).commit();
    }
}

}

详细信息片段

首先创建片段。片段生命周期确保 onCreateView() 为片段构建布局。它使用 textview 构建片段 - text.setText(Shakespeare.DIALOGUE[getShownIndex()]) - 并将其附加到滚动条 (ScrollView) 并返回（并呈现）绘制的视图。

    // This is the secondary fragment, displaying the details of a particular
    // item.        

    public static class DetailsFragment extends Fragment {

                **snippet**

                public int getShownIndex() {
                            return getArguments().getInt("index", 0);
                }

                // The system calls this when it's time for the fragment to draw its
                // user interface for the first time. To draw a UI for your fragment,
                // you must return a View from this method that is the root of your
                // fragment's layout. You can return null if the fragment does not
                // provide a UI.

                // We create the UI with a scrollview and text and return a reference to
                // the scoller which is then drawn to the screen

                @Override
                public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                        Bundle savedInstanceState) {

                    **snippet**

                        // programmatically create a scrollview and textview for the text in
                        // the container/fragment layout. Set up the properties and add the view

                        ScrollView scroller = new ScrollView(getActivity());
                        TextView text = new TextView(getActivity());
                        int padding = (int) TypedValue.applyDimension(
                                            TypedValue.COMPLEX_UNIT_DIP, 4, getActivity()
                                                          .getResources().getDisplayMetrics());
                        text.setPadding(padding, padding, padding, padding);
                        scroller.addView(text);
                        text.setText(Shakespeare.DIALOGUE[getShownIndex()]);
                        return scroller;
                }
    }