在POST调用后在Android应用中设置TextView

Question

我正在开发一个Android应用程序，通过API对网站进行调用。调用完成后返回它，然后将该响应放入另一个片段的TextView中。但是，每次运行应用程序时，如果fragment_main中未包含fragment_main，则会强制关闭。我无法弄清楚为什么它找不到我的身份证，但令人沮丧。此外，如果我在activity_main中包含fragment_main，那么它永远不会消失。这是代码......

MainActivity.java -------------

    package com.horizonservers.horizon;

import android.app.ProgressDialog;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.design.widget.TextInputEditText;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.webkit.WebViewFragment;
import android.widget.TextView;

import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.Buffer;

import javax.net.ssl.HttpsURLConnection;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener, ProfileFragment.OnFragmentInteractionListener, MainFragment.OnFragmentInteractionListener {

    TextView mResult;

    NavigationView navigationView = null;
    Toolbar toolbar = null;

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

        //Set the main fragment
        MainFragment fragment = new MainFragment();
        android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.fragment_container, fragment);
        fragmentTransaction.commit();
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);


        mResult = (TextView) findViewById(R.id.tv_result);


        // Make GET request to server
        //new 


        //Make POST request to server
        new PostDataTask().execute("https://thewebsite.com/api/v1/blah");
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, 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();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.main) {
            //Set the main fragment
            MainFragment fragment = new MainFragment();
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();
        } else if (id == R.id.player_profile) {
            //Set the main fragment
            ProfileFragment fragment = new ProfileFragment();
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();

        } else if (id == R.id.map_tracker) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
    public void onFragmentInteraction(Uri uri){
        //you can leave it empty
    }

    class GetDataTask extends AsyncTask<String, Void, String> {

        ProgressDialog progressDialog;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            progressDialog = new ProgressDialog(MainActivity.this);
            progressDialog.setMessage("Loading Data...");
            progressDialog.show();
        }

        @Override
        protected String doInBackground(String... params) {

            try {
                return getData(params[0]);
            } catch (IOException ex){
                return "Network Error!";
            }
        }

        @Override
        protected void onPostExecute(String result) {

            //Set data to be shown on TextView
            mResult.setText(result);

            //cancel progressdialog
            if(progressDialog != null) {
                progressDialog.dismiss();
            }
            super.onPostExecute(result);
        }

        private String getData(String urlPath) throws IOException{


            BufferedReader bufferedReader = null;
            StringBuilder result = new StringBuilder();
            //Initialize request with server

            try {
                URL url = new URL(urlPath);
                HttpURLConnection urlConnection = (HttpsURLConnection) url.openConnection();
                urlConnection.setReadTimeout(10000 /* 10 second time out */);
                urlConnection.setConnectTimeout(10000 /* 10 second time out */);
                urlConnection.setRequestMethod("GET");
                urlConnection.setRequestProperty("Content-type", "application/json");
                urlConnection.connect();

                //Read data from server
                InputStream inputStream = urlConnection.getInputStream();
                bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                String line;

                while((line = bufferedReader.readLine()) != null){
                    result.append(line).append("\n");
                }



            } finally {
                if(bufferedReader != null){
                    bufferedReader.close();
                }
            }
            return result.toString();
        }
    }


    class PostDataTask extends AsyncTask<String, Void, String> {

        ProgressDialog progressDialog;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            progressDialog = new ProgressDialog(MainActivity.this);
            progressDialog.setMessage("Inserting data...");
            progressDialog.show();
        }

        @Override
        protected String doInBackground(String... params) {

            try {
                return postData(params[0]);
            } catch (IOException ex) {
                return "Network error !";
            } catch (JSONException ex) {
                return "Data Invalid !";
            }
        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);

            mResult.setText(result);

            if (progressDialog != null) {
                progressDialog.dismiss();
            }
        }

        private String postData(String urlPath) throws IOException, JSONException {

            StringBuilder result = new StringBuilder();
            BufferedWriter bufferedWriter = null;
            BufferedReader bufferedReader = null;

            try {
                //Create data to send to server
                JSONObject dataToSend = new JSONObject();
                dataToSend.put("apikey", "UPj07lqWdetOWrk9M8Ya9UZzeIAizjr4sYQRKzkHFYm1KaQDopytCFq9HHCerwNy");
                dataToSend.put("steamid", "STEAM_0:1:90345825");
                dataToSend.put("maptype", "surf");

                //Initialize and config request, then connect to server.
                URL url = new URL(urlPath);
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setReadTimeout(10000 /* milliseconds */);
                urlConnection.setConnectTimeout(10000 /* milliseconds */);
                urlConnection.setRequestMethod("POST");
                urlConnection.setDoOutput(true);  //enable output (body data)
                urlConnection.setRequestProperty("Content-Type", "application/json");// set header
                urlConnection.connect();

                //Write data into server
                OutputStream outputStream = urlConnection.getOutputStream();
                bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream));
                bufferedWriter.write(dataToSend.toString());
                bufferedWriter.flush();

                //Read data response from server
                InputStream inputStream = urlConnection.getInputStream();
                bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                String line;
                while ((line = bufferedReader.readLine()) != null) {
                    result.append(line).append("&");
                }
            } finally {
                if (bufferedReader != null) {
                    bufferedReader.close();
                }
                if (bufferedWriter != null) {
                    bufferedWriter.close();
                }
            }

            return result.toString();
        }
    }


}

这是MainFragment.java，它会使fragment_main.xml文件膨胀。

FragmentMain.java

package com.horizonservers.horizon;

import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.CookieManager;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.webkit.WebViewFragment;
import android.widget.Button;
import android.widget.TextView;


/**
 * A simple {@link Fragment} subclass.
 * Activities that contain this fragment must implement the
 * {@link MainFragment.OnFragmentInteractionListener} interface
 * to handle interaction events.
 * Use the {@link MainFragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class MainFragment extends Fragment {


    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;

    private OnFragmentInteractionListener mListener;

    public MainFragment() {
        // Required empty public constructor
    }

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment MainFragment.
     */
    // TODO: Rename and change types and number of parameters
    public static MainFragment newInstance(String param1, String param2) {
        MainFragment fragment = new MainFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_main, container, false);
    }

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


    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    /**
     * This interface must be implemented by activities that contain this
     * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     * <p/>
     * See the Android Training lesson <a href=
     * "http://developer.android.com/training/basics/fragments/communicating.html"
     * >Communicating with Other Fragments</a> for more information.
     */
    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
    }

}

这是activity_main.xml，大部分都没有改变。

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout 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/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">

    <include
        layout="@layout/app_bar_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />


    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/nav_header_main"
        app:menu="@menu/activity_main_drawer" />

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

最后，fragment_main.xml

fragment_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/tv_result"
        android:layout_width="wrap_content"
        android:layout_height="-20dp"
        android:textSize="17sp"
        android:textStyle="bold"
        android:text="Test HTTP request !" />
</RelativeLayout>

现在，当我运行app而没有在activity_main中包含fragment_main时，我收到此错误

  

java.lang.NullPointerException：尝试在空对象引用上调用虚方法'void android.widget.TextView.setText（java.lang.CharSequence）'                                                                                   在com.horizo​​nservers.horizo​​n.MainActivity $ PostDataTask.onPostExecute（MainActivity.java:257）                                                                                   在com.horizo​​nservers.horizo​​n.MainActivity $ PostDataTask.onPostExecute（MainActivity.java:228）

任何人都可以帮助我，我还在学习，请原谅我。

Answer 1

tv_result位于fragment_main，您正在Activity初始化它。需要在fragment初始化它。您在views。

中找不到其他布局的activity

初始化片段onCreateView中的视图，如：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View v = inflater.inflate(R.layout.fragment_main, container, false);
    mResult = (TextView) v.findViewById(R.id.tv_result);
    return view;
}

在获得结果后，使用eventBus或界面将fragment发送给您，并在Fragment而不是Activity中设置文字。

Answer 2

好的，谢谢大家的帮助！我想到了！我把所有东西都移到了FragmentMain而不是MainActivity，并在它完成通话后让它膨胀！非常感谢你的帮助！这是更新的代码，以防将来有人需要它。

<强> MainFragment

package com.horizonservers.horizon;

import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;

import javax.net.ssl.HttpsURLConnection;


/**
 * A simple {@link Fragment} subclass.
 * Activities that contain this fragment must implement the
 * {@link MainFragment.OnFragmentInteractionListener} interface
 * to handle interaction events.
 * Use the {@link MainFragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class MainFragment extends Fragment {


    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;

    private TextView mResult;

    private OnFragmentInteractionListener mListener;

    public MainFragment() {
        // Required empty public constructor
    }

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment MainFragment.
     */
    // TODO: Rename and change types and number of parameters
    public static MainFragment newInstance(String param1, String param2) {
        MainFragment fragment = new MainFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }

        new PostDataTask().execute("https://www.horizonservers.net/api/v1/PlayerInfo");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View v = inflater.inflate(R.layout.fragment_main, container, false);
        mResult = (TextView) v.findViewById(R.id.tv_result);
        return v;
    }

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


    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    /**
     * This interface must be implemented by activities that contain this
     * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     * <p>
     * See the Android Training lesson <a href=
     * "http://developer.android.com/training/basics/fragments/communicating.html"
     * >Communicating with Other Fragments</a> for more information.
     */
    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
    }

    class PostDataTask extends AsyncTask<String, Void, String> {

        ProgressDialog progressDialog;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

        }

        @Override
        protected String doInBackground(String... params) {

            try {
                return postData(params[0]);
            } catch (IOException ex) {
                return "Network error !";
            } catch (JSONException ex) {
                return "Data Invalid !";
            }
        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);

            mResult.setText(result);

            if (progressDialog != null) {
                progressDialog.dismiss();
            }
        }

        private String postData(String urlPath) throws IOException, JSONException {

            StringBuilder result = new StringBuilder();
            BufferedWriter bufferedWriter = null;
            BufferedReader bufferedReader = null;

            try {
                //Create data to send to server
                JSONObject dataToSend = new JSONObject();
                dataToSend.put("apikey", "UPj07lqWdetOWrk9M8Ya9UZzeIAizjr4sYQRKzkHFYm1KaQDopytCFq9HHCerwNy");
                dataToSend.put("steamid", "STEAM_0:1:90345825");
                dataToSend.put("maptype", "surf");

                //Initialize and config request, then connect to server.
                URL url = new URL(urlPath);
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setReadTimeout(10000 /* milliseconds */);
                urlConnection.setConnectTimeout(10000 /* milliseconds */);
                urlConnection.setRequestMethod("POST");
                urlConnection.setDoOutput(true);  //enable output (body data)
                urlConnection.setRequestProperty("Content-Type", "application/json");// set header
                urlConnection.connect();

                //Write data into server
                OutputStream outputStream = urlConnection.getOutputStream();
                bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream));
                bufferedWriter.write(dataToSend.toString());
                bufferedWriter.flush();

                //Read data response from server
                InputStream inputStream = urlConnection.getInputStream();
                bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                String line;
                while ((line = bufferedReader.readLine()) != null) {
                    result.append(line).append("&");
                }
            } finally {
                if (bufferedReader != null) {
                    bufferedReader.close();
                }
                if (bufferedWriter != null) {
                    bufferedWriter.close();
                }
            }

            return result.toString();
        }
    }
}