为活动中的片段中的ListView设置ListView适配器

时间：2017-05-20 22:59:26

标签： java android listview android-fragments

我需要设置一个ListView的Adapter，它位于Activity的Fragment中。 我尝试使用下面的代码从Activity中设置适配器，但它返回NullPointerException，可能是因为片段尚未加载。

    ListView gradeListView = (ListView) this.findViewById(R.id.gradeListView);
    gradeListView.setAdapter(new SimpleAdapter(this, item_list, list_layout, list_input, layout_values));

有没有办法在Fragment加载后运行上面的代码，或者更好的方法完全执行此操作？我试图使用一种方法将Frag内部设置为适配器，但是我仍然需要等待片段加载才能从Activity中发起它，否则我仍然会收到NullPointerException。我还需要将ArrayList<HashMap<String, String>>放入一个包中，如果我打算使用该方法，则没有关于如何操作的文档。

我还试图启动一个方法，该方法保存位于活动内部的设置适配器代码，该代码仍位于片段的onActivityCreated()方法中，该方法仍返回NullPointerException。

我没有正确地从Activity中引用ListView元素，还是有办法等待Fragment加载，所以我没有收到错误？

TabbedActivity.java /主要父活动 

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

    // Create the adapter that will return a fragment for each of the three
    // primary sections of the activity.
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.container);
    mViewPager.setOffscreenPageLimit(6);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(mViewPager);

    // ...

    interpretGrades(retrieveGrades());
}

public void interpretGrades(String input) {
    // take CLASSES~~MAINCLASSDIVIDER~~GRADES
    // turn it into Classes = Classes
    //              Grades = Grades
    final String[] ServerResponse = input.split("~~MAINCLASSDIVIDER~~");
    final String[] Classes = ServerResponse[0].split(";");
    final String[] Grades = ServerResponse[1].split(";");

    ArrayList<HashMap<String, String>> item_list = new ArrayList<HashMap<String, String>>();

    for (int i = 0; i < Classes.length; i++) {
        HashMap<String, String> item = new HashMap<String, String>();
        String[] ClassSplit = Classes[i].split("-");
        String Period = ClassSplit[0];
        String Class = ClassSplit[1];
        item.put("Period", Period);
        // --.substring(1, --.length())     removes first character from string (in this case, a whitespace from the class name)
        item.put("Class", Class.substring(1, Class.length()));
        item.put("Grade", Grades[i]);

        item_list.add(item);
    }

    String[] list_input = new String[] { "Period", "Class", "Grade" };

    // PUT THE STRING VALUES FROM list_input INTO THE XML LAYOUT VALUES
    int[] layout_values = new int[] { android.R.id.text1, android.R.id.text2, R.id.grade};

    // LISTVIEW LAYOUT (XML FILE)
    int list_layout = grade_list;

    ListView gradeListView = (ListView) this.findViewById(R.id.gradeListView);
    gradeListView.setAdapter(new SimpleAdapter(this, item_list, list_layout, list_input, layout_values));
}

Tab2Pulse.java / Fragment 

public class Tab2Pulse extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        mainView = inflater.inflate(R.layout.tab2chat, container, false);
        return mainView;
    }
}

tab2chat.xml /片段布局 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/tab2chat"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
android:orientation="vertical">

<TextView
    android:id="@+id/textView5"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="TextView" />

<android.support.v4.widget.SwipeRefreshLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/swipeContainer"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:id="@+id/gradeListView"
        style="@android:style/Widget.Material.Light.ListView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true" />
</android.support.v4.widget.SwipeRefreshLayout>

</LinearLayout>

activity_tabbed.xml /主要活动布局 

<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/main_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="software.endeavor.projectg.TabbedActivity">


<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dip"
        android:layout_weight="1"
        android:fitsSystemWindows="true"
        android:orientation="vertical">

        <android.support.design.widget.AppBarLayout
            android:id="@+id/appbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@drawable/main_gradient"
            android:paddingTop="@dimen/appbar_padding_top"
            android:theme="@style/AppTheme.AppBarOverlay">

            <View
                android:layout_width="match_parent"
                android:layout_height="12dp" />

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:background="@drawable/main_gradient"
                app:layout_scrollFlags="scroll|enterAlways"
                app:popupTheme="@style/AppTheme.PopupOverlay">

            </android.support.v7.widget.Toolbar>

            <android.support.design.widget.TabLayout
                android:id="@+id/tabs"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:tabIndicatorColor="@android:color/white" />

        </android.support.design.widget.AppBarLayout>

        <View
            android:id="@+id/toolbar_shadow"
            android:layout_width="match_parent"
            android:layout_height="12dp"
            android:layout_below="@id/toolbar"
            android:background="@drawable/toolbar_dropshadow" />

        <!--<android.support.v4.widget.SwipeRefreshLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/swipeContainer"
    android:layout_width="368dp"
    android:layout_height="495dp">-->

        <android.support.v4.view.ViewPager
            android:id="@+id/container"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior" />

        <android.support.design.widget.FloatingActionButton
            android:id="@+id/fab"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="end|bottom"
            android:layout_margin="@dimen/fab_margin"
            app:srcCompat="@android:drawable/ic_dialog_email" />

        <!--</android.support.v4.widget.SwipeRefreshLayout>-->

    </LinearLayout>

    <View
        android:id="@+id/view"
        android:layout_width="match_parent"
        android:layout_height="@*android:dimen/navigation_bar_height"
        android:background="@drawable/login_gradient" />
</LinearLayout>

</android.support.design.widget.CoordinatorLayout>

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