Java 方法getApplicationContext（）未定义-片段问题

我收到以下错误： 方法getApplicationContext（）未定义 类型Fragment1的findViewById（int）方法未定义

当我的类扩展到一个活动而不是一个片段时，这些错误似乎被消除了，但是这个活动仍然是一个片段是很重要的，所以我不太确定如何解决这个问题

任何帮助都将不胜感激。 提前谢谢

下面是代码

public class Fragment1 extends Fragment {

    private String currentUserId;
    private ArrayAdapter<String> namesArrayAdapter;
    private ArrayList<String> names;
    private ListView usersListView;
    private Button logoutButton;
    String userGender = ParseUser.getCurrentUser().getString("Gender");
    String activityName = ParseUser.getCurrentUser().getString("ActivityName");
    Number maxDistance = ParseUser.getCurrentUser().getNumber("Maximum_Distance");


    String userLookingGender = ParseUser.getCurrentUser().getString("Looking_Gender");
    Number minimumAge = ParseUser.getCurrentUser().getNumber("Minimum_Age");
    Number maximumAge = ParseUser.getCurrentUser().getNumber("Maximum_Age");
    Number userage = ParseUser.getCurrentUser().getNumber("Age");


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        if (container == null){
            return null;
        }

        return (LinearLayout)inflater.inflate(R.layout.fragment1_layout, 
                container,false);

    logoutButton = (Button) findViewById(R.id.logoutButton);
    logoutButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            ParseUser.logOut();
            Intent intent = new Intent(getApplicationContext(), LoginActivity.class);
            startActivity(intent);
        }
    });

    setConversationsList();
}
private void setConversationsList() {
    currentUserId = ParseUser.getCurrentUser().getObjectId();
    names = new ArrayList<String>();
    // String userActivitySelectionName = null;

    ParseQuery<ParseUser> query = ParseUser.getQuery();

    //  query.whereEqualTo("ActivityName",userActivitySelectionName);

    query.whereNotEqualTo("objectId", ParseUser.getCurrentUser().getObjectId());
    // users with Gender = currentUser.Looking_Gender
    query.whereEqualTo("Gender", userLookingGender);
    // users with Looking_Gender = currentUser.Gender
    query.whereEqualTo("Looking_Gender", userGender);
    query.setLimit(1);
    query.whereEqualTo("ActivityName", activityName);
    query.whereGreaterThanOrEqualTo("Minimum_Age", minimumAge).whereGreaterThanOrEqualTo("Age", userage);
    query.whereLessThanOrEqualTo("Maximum_Age", maximumAge).whereLessThanOrEqualTo("Age", userage);
    //  query.whereWithinKilometers("Maximum_Distance", point, maxDistance)





    query.findInBackground(new FindCallback<ParseUser>() {

        public void done(List<ParseUser> userList, ParseException e) {
            if (e == null) {
                for (int i=0; i<userList.size(); i++) {
                    names.add(userList.get(i).get("Name").toString());
                    names.add(userList.get(i).get("Headline").toString());
                    names.add(userList.get(i).get("Age").toString());

                    //       names.add(userList.get(i).getParseObject("ProfilePicture").;


                }




                usersListView = (ListView)findViewById(R.id.usersListView);
                namesArrayAdapter =
                        new ArrayAdapter<String>(getApplicationContext(),
                                R.layout.user_list_item, names);
                usersListView.setAdapter(namesArrayAdapter);

                usersListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> a, View v, int i, long l) {
                        openConversation(names, i);
                    }
                });

            } else {
                Toast.makeText(getApplicationContext(),
                        "Error loading user list",
                        Toast.LENGTH_LONG).show();
            }
        }
    });
}

public void openConversation(ArrayList<String> names, int pos) {
    ParseQuery<ParseUser> query = ParseUser.getQuery();
    query.whereEqualTo("Name", names.get(pos));
    query.findInBackground(new FindCallback<ParseUser>() {
        public void done(List<ParseUser> user, ParseException e) {
            if (e == null) {
                Intent intent = new Intent(getApplicationContext(), MessagingActivity.class);
                intent.putExtra("RECIPIENT_ID", user.get(0).getObjectId());
                startActivity(intent);
            } else {
                Toast.makeText(getApplicationContext(),
                        "Error finding that user",
                        Toast.LENGTH_SHORT).show();
            }
        }
    });
}
}

下面是调用片段的活动页面

import java.util.List;
import java.util.Vector;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.view.Menu;
import android.view.MenuItem;



public class usermatch extends FragmentActivity {
    private PageAdapter mPagerAdapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.viewpager_layout);
        initialisePaging();

    }

    private void initialisePaging() {
        // TODO Auto-generated method stub
        List<Fragment> fragments = new Vector<Fragment>();
        fragments.add(Fragment.instantiate(this, Fragment1.class.getName()));
        fragments.add(Fragment.instantiate(this, Fragment2.class.getName()));
        fragments.add(Fragment.instantiate(this, Fragment3.class.getName()));
        mPagerAdapter = new PageAdapter(this.getSupportFragmentManager(), fragments);
        ViewPager pager = (ViewPager) findViewById(R.id.viewpager);
        pager.setAdapter(mPagerAdapter);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.mood, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

改变

到

---

您可以使用

getActivity（）

获取包含片段的活动

因此，

getActivity（）.getApplicationContext（）

将起作用

getActivity（）.findViewById（int）

也可以工作

---

但是，请确保不要在onActivityCreated（）之前使用

getActivity（）

，因为在此之前它将返回null。

您可以从onAttach（）访问上下文，如下面的示例所示

 @Override
    public void onAttach(@NonNull Context context) {


        super.onAttach(context);
    }

---

感谢您的及时回复，我已经应用了您的建议，但是，以下行似乎有问题：logoutButton=（Button）getActivity（）.findviewbyd（R.id.logoutButton）@Eran什么abt'Intent Intent=new Intent（getActivity（），LoginActivity.class）；'这也会起作用。@SaravanarajaT取决于您希望使用的上下文

getActivity（）

本身可以作为上下文（因为它是上下文的一个子类）。getActivity（）.getApplicationContext（）返回当前进程的单个全局应用程序对象。@user3907211您在

onCreateView（）

中进行此调用，该调用在

onActivityCreated（）

之前调用，因此

getActivity（）

可能返回null。你能把这段代码移到

onActivityCreated（）

？@user3907211在

usermatch.java

，第32行有什么内容？我应该使用getActivity（）。getApplicationContext（）还是getActivity（）谢谢你的响应对于我来说，getActivity（）是最好的选择，因为在一个片段中永远不会为空。谢谢你的回答和支持。在启动活动时，我收到了一个意外的空指针异常错误作为响应。我已经在我最初的帖子的更新部分更新了我的问题。如果你能调查一下，我将不胜感激。

import java.util.List;
import java.util.Vector;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.view.Menu;
import android.view.MenuItem;



public class usermatch extends FragmentActivity {
    private PageAdapter mPagerAdapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.viewpager_layout);
        initialisePaging();

    }

    private void initialisePaging() {
        // TODO Auto-generated method stub
        List<Fragment> fragments = new Vector<Fragment>();
        fragments.add(Fragment.instantiate(this, Fragment1.class.getName()));
        fragments.add(Fragment.instantiate(this, Fragment2.class.getName()));
        fragments.add(Fragment.instantiate(this, Fragment3.class.getName()));
        mPagerAdapter = new PageAdapter(this.getSupportFragmentManager(), fragments);
        ViewPager pager = (ViewPager) findViewById(R.id.viewpager);
        pager.setAdapter(mPagerAdapter);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.mood, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

08-15 17:42:28.863: E/AndroidRuntime(4974): FATAL EXCEPTION: main
08-15 17:42:28.863: E/AndroidRuntime(4974): Process: com.dooba.beta, PID: 4974
08-15 17:42:28.863: E/AndroidRuntime(4974): java.lang.NullPointerException
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.dooba.beta.Fragment1$1.done(Fragment1.java:108)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.parse.FindCallback.internalDone(FindCallback.java:45)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.parse.FindCallback.internalDone(FindCallback.java:1)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.parse.Parse$6$1.run(Parse.java:888)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.os.Handler.handleCallback(Handler.java:733)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.os.Handler.dispatchMessage(Handler.java:95)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.os.Looper.loop(Looper.java:136)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.app.ActivityThread.main(ActivityThread.java:5017)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at java.lang.reflect.Method.invokeNative(Native Method)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at java.lang.reflect.Method.invoke(Method.java:515)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at dalvik.system.NativeStart.main(Native Method)

Intent intent = new Intent(getApplicationContext(), LoginActivity.class);

Intent intent = new Intent(getActivity(), LoginActivity.class);

 @Override
    public void onAttach(@NonNull Context context) {


        super.onAttach(context);
    }