将数据从一个活动发送到第二个活动的片段

Question

次要活动（通过意图向主活动发送“endpoint”字符串）：

        Intent intent = new Intent(Secondary.this,Main.class);
        intent.putExtra("endpoint",endpoint);
        startActivity(intent);

主活动（从次要活动获取字符串）：

    public void onNavigationDrawerItemSelected(int position) {
    // update the main content by replacing fragments
    FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.beginTransaction()
            .replace(R.id.container, PlaceholderFragment.newInstance(position))
            .commit();
    switch (position) {
        case 0:
            Bundle args = new Bundle();
            args.putString("endpoint",getIntent().getExtras().getString("endpoint"));
            Fragment1 fragment = new Fragment1();
            fragment1.setArguments(args);
            fragmentManager.beginTransaction().replace(R.id.container, Fragment1.newInstance(position)).commit();
            break;
        case 1:
            fragmentManager.beginTransaction().replace(R.id.container, Fragment2newInstance(position)).commit();
            break;
        case 2:
            fragmentManager.beginTransaction().replace(R.id.container, Fragment3.newInstance(position)).commit();
            break;
        case 3: ...

在Fragment类上，我试图在TextView上显示数据：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    String endpoints = getActivity().getIntent().getStringExtra("endpointStr");
    View rootView = inflater.inflate(R.layout.fragment_overview, container, false);
    TextView textView = (TextView) rootView.findViewById(R.id.overviewTV);
    textView.setText(endpoint);
    return rootView;
}

        **Caused by: java.lang.NullPointerException**
        at com.Main.app.Main.onNavigationDrawerItemSelected(Main.java:65)
        at com.Main.app.NavigationDrawerFragment.selectItem(NavigationDrawerFragment.java:205)
        at com.Main.app.NavigationDrawerFragment.onCreate(NavigationDrawerFragment.java:79)
        at android.app.Fragment.performCreate(Fragment.java:1678)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:859)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1040)
        at android.app.FragmentManagerImpl.addFragment(FragmentManager.java:1142)
        at android.app.Activity.onCreateView(Activity.java:4786)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:689)

如何修复它并将字符串从一个活动发送到另一个活动上的片段？

下面是XML：

<!-- A DrawerLayout is intended to be used as the top-level content view using match_parent for both width and height to consume the full space available. -->
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">
    <android.support.v4.widget.DrawerLayout
        android:id="@+id/drawer_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#ffffff"
        tools:context=".Stackerz">

        <!-- As the main content view, the view below consumes the entire
             space available using match_parent in both dimensions. -->
        <FrameLayout
            android:id="@+id/container"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            />

        <!-- android:layout_gravity="start" tells DrawerLayout to treat
             this as a sliding drawer on the left side for left-to-right
             languages and on the right side for right-to-left languages.
             If you're not building against API 17 or higher, use
             android:layout_gravity="left" instead. -->
        <!-- The drawer is given a fixed width in dp and extends the full height of
             the container. -->
        <fragment android:id="@+id/navigation_drawer"
            android:layout_width="@dimen/navigation_drawer_width"
            android:layout_height="match_parent"
            android:layout_gravity="start"
            android:name="com.xxxxxx.app.NavigationDrawerFragment"
            tools:layout="@layout/fragment_navigation_drawer" />

    </android.support.v4.widget.DrawerLayout>
</FrameLayout>

Answer 1

好的，这就是您的Constants类应该是什么样子的。

public class Constants {

public static Constants constants=null;

public static Constants shared(){
    if (constants==null){
        constants = new Constants();
    }
    return constants;
}

public static String endpoint;

public static String getEndpoint() {
    return endpoint;
}

public static void setEndpoint(String endpoint) {
    Constants.endpoint = endpoint;
}

}

现在，在第二个活动中，这样做：

    Constants.shared().setEndpoint(endpoint);
    Intent intent = new Intent(Secondary.this,Main.class);
    startActivity(intent);

在碎片类中，执行以下操作：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                     Bundle savedInstanceState) {
String endpoint = Constants.shared().getEndpoint;
View rootView = inflater.inflate(R.layout.fragment_overview, container, false);
TextView textView = (TextView) rootView.findViewById(R.id.overviewTV);
textView.setText(endpoint);
return rootView;
}