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我正在開發一個通過API向網站發送郵件的Android應用程序。調用完成並返回後，將該響應放入另一個片段的TextView中。但是，每次運行應用程序時，如果fragment_main未包含在activity_main中，則強制關閉。我無法弄清楚爲什麼找不到我的身份證，但令人沮喪。另外，如果我在activity_main中包含fragment_main，那麼它永遠不會消失。下面是代碼...在POST通話後在Android應用程序中設置TextView
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();
}
}
}
下面是MainFragment.java它膨脹的fragment_main.xml文件。
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);
}
}
這裏是activity_main.xml中，大多是不變的。
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>
最後，
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>
現在，當我運行不fragment_main應用程序被列入fragment_main.xml activity_main我得到這個錯誤
顯示java.lang.NullPointerException：嘗試調用虛擬方法 '無效android.widget.TextView.setText（java.lang.CharSequence中）' 上在com.horizonservers.horizon.MainActivity $ PostDataTask空對象引用 。 onPostExecute（MainActivity.java:257） 在com.horizonservers.horizon.MainActivity $ PostDataTask.onPostExecute（MainActivity.java:228）
誰能幫我，我還在學習，所以請原諒我。
tv_result，它使用的是要顯示的已通過調用的setContentView（）方法設置爲內容視圖activity_main.xml中文件中沒有數據的文本視圖，因此不會在mResult中獲取textview引用，因此它顯示你空指針異常。 – Vickyexpert
我嘗試從setContentView中的activity_main切換到fragment_main，但它崩潰並且在我這樣做時無法打開。 – Destry
你不能像這樣切換它，首先讓我知道你確切想要做什麼， 你想調用活動類的Web服務和設置結果片段？或者你想在活動中顯示片段並調用Web服務？ – Vickyexpert