我是Android应用程序开发和Java编程的新手，目前，我正在开发一个项目，用于从我的数据库中检索服务的状态。但是，每当我尝试提交跟踪ID时，应用程序都将停止工作。
MainActivity.java
package com.example.trackstatus;
import com.example.testapp.R;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends Activity {
Button btnViewStatus;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Buttons
btnViewStatus = (Button) findViewById(R.id.btnViewStatus);
// view products click event
btnViewStatus.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
// Launching View status activity
Intent i = new Intent(getApplicationContext(), ViewTrackingStatusActivity.class);
startActivity(i);
}
});
}}
TrackStatus清单
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package = "com.example.trackstatus"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="20" />
<!-- Internet Permissions -->
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<!-- View Tracking Status Activity -->
<activity
android:name=".ViewTrackingStatusActivity"
android:label="View Tracking Status" >
</activity>
</application>
</manifest>
ViewTrackingStatusActivity.java
package com.example.trackstatus;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.example.testapp.R;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class ViewTrackingStatusActivity extends Activity{
TextView textView1;
EditText trackingNumberText;
Button btnViewStatus;
String tid;
String tracking;
// Progress Dialog
private ProgressDialog pDialog;
// JSON parser class
JSONParser jsonParser = new JSONParser();
// url to get service status
private static String url = "http://10.0.2.2/1201716f/android%20connect/get_svc.php?tid=0";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_TRACKING = "tracking";
private static final String TAG_TID = "tid";
public String trackingno;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView1 = (TextView) findViewById(R.id.textView1);
trackingNumberText = (EditText) findViewById(R.id.trackingNumberText);
trackingno = trackingNumberText.getText().toString();
btnViewStatus = (Button) findViewById(R.id.btnViewStatus);
Intent intent = getIntent();
tid = intent.getStringExtra(TAG_TID);
// Getting tracking status details in background thread
new GetStatusDetails().execute();
//Toast.makeText(getApplicationContext(),"Hello",
// Toast.LENGTH_LONG).show();
}
class GetStatusDetails extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(ViewTrackingStatusActivity.this);
pDialog.setMessage("Loading details");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
protected String doInBackground(String... params) {
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
// Check for success tag
int success;
try {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("tid", trackingno));
// getting product details by making HTTP request
// Note that product details url will use GET request
JSONObject json = jsonParser.makeHttpRequest(url, "GET", params);
// check your log for json response
Log.d("Tracking Status Details", json.toString());
// json success tag
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// successfully received product details
JSONArray trackingObj = json.getJSONArray(TAG_TRACKING); // JSON Array
// get first product object from JSON Array
JSONObject tracking = trackingObj.getJSONObject(0);
// display tracking status in ToastBox
Toast.makeText(ViewTrackingStatusActivity.this,json.getString(TAG_TRACKING),Toast.LENGTH_LONG).show();
}
else
{
//service with tid not found
Toast.makeText(getApplicationContext(),"Service not found!",Toast.LENGTH_LONG).show();
}
}
catch (JSONException e)
{
e.printStackTrace();
}
}
});
return null;
}
}
}
JSONParser.java
package com.example.trackstatus;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
// function get json from url
// by making HTTP POST or GET mehtod
public JSONObject makeHttpRequest(String url, String method,
List<NameValuePair> params) {
// Making HTTP request
try {
// check for request method
if(method == "POST"){
// request method is POST
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}
else if(method == "GET"){
// request method is GET
DefaultHttpClient httpClient = new DefaultHttpClient();
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
json = sb.toString();
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
}
}
logcat的
08-19 23:52:46.644: D/AndroidRuntime(3809): Shutting down VM
08-19 23:52:46.644: W/dalvikvm(3809): threadid=1: thread exiting with uncaught exception (group=0x41b37700)
08-19 23:52:46.654: E/AndroidRuntime(3809): FATAL EXCEPTION: main
08-19 23:52:46.654: E/AndroidRuntime(3809): android.os.NetworkOnMainThreadException
08-19 23:52:46.654: E/AndroidRuntime(3809): at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1133)
08-19 23:52:46.654: E/AndroidRuntime(3809): at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:84)
08-19 23:52:46.654: E/AndroidRuntime(3809): at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
08-19 23:52:46.654: E/AndroidRuntime(3809): at libcore.io.IoBridge.connect(IoBridge.java:112)
08-19 23:52:46.654: E/AndroidRuntime(3809): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
08-19 23:52:46.654: E/AndroidRuntime(3809): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:459)
08-19 23:52:46.654: E/AndroidRuntime(3809): at java.net.Socket.connect(Socket.java:842)
08-19 23:52:46.654: E/AndroidRuntime(3809): at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:119)
08-19 23:52:46.654: E/AndroidRuntime(3809): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:144)
08-19 23:52:46.654: E/AndroidRuntime(3809): at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
08-19 23:52:46.654: E/AndroidRuntime(3809): at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
08-19 23:52:46.654: E/AndroidRuntime(3809): at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
08-19 23:52:46.654: E/AndroidRuntime(3809): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
08-19 23:52:46.654: E/AndroidRuntime(3809): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
08-19 23:52:46.654: E/AndroidRuntime(3809): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
08-19 23:52:46.654: E/AndroidRuntime(3809): at com.example.trackstatus.JSONParser.makeHttpRequest(JSONParser.java:63)
08-19 23:52:46.654: E/AndroidRuntime(3809): at com.example.trackstatus.ViewTrackingStatusActivity$GetStatusDetails$1.run(ViewTrackingStatusActivity.java:92)
08-19 23:52:46.654: E/AndroidRuntime(3809): at android.os.Handler.handleCallback(Handler.java:730)
08-19 23:52:46.654: E/AndroidRuntime(3809): at android.os.Handler.dispatchMessage(Handler.java:92)
08-19 23:52:46.654: E/AndroidRuntime(3809): at android.os.Looper.loop(Looper.java:137)
08-19 23:52:46.654: E/AndroidRuntime(3809): at android.app.ActivityThread.main(ActivityThread.java:5293)
08-19 23:52:46.654: E/AndroidRuntime(3809): at java.lang.reflect.Method.invokeNative(Native Method)
08-19 23:52:46.654: E/AndroidRuntime(3809): at java.lang.reflect.Method.invoke(Method.java:525)
08-19 23:52:46.654: E/AndroidRuntime(3809): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
08-19 23:52:46.654: E/AndroidRuntime(3809): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:554)
08-19 23:52:46.654: E/AndroidRuntime(3809): at dalvik.system.NativeStart.main(Native Method)
08-19 23:52:49.086: I/Process(3809): Sending signal. PID: 3809 SIG: 9
答案 0 :(得分：2)
根据您的LogCat消息：
Caused by: java.lang.NullPointerException at com.example.trackstatus.ViewTrackingStatusActivity.onCreate(ViewTrackingStatusActivity.java:55)
你错过了：
setContentView(R.layout.your_layout);
必须声明您的EditText trackingNumberText。
这就是trackingNumberText为空的原因
trackingNumberText = (EditText) findViewById(R.id.trackingNumberText);
更多信息：
由于您有以下新例外： NetworkOnMainThreadException
android.os.NetworkOnMainThreadException at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1133)
您必须实施 AsyncTask
的使用嘿！你不需要在Asynctask的runOnUiThread方法中使用doInBackground()：P：
protected String doInBackground(String... params) {
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
在UI线程上移动暗示操作的行，如
Toast.makeText(getApplicationContext(),"Service not found!",Toast.LENGTH_LONG).show();
到onPostExecute()
Asynctask方法
答案 1 :(得分：0)
错误在Line55
String trackingno = trackingNumberText.getText().toString();
trackingNumberText NULL
而是尝试进行NULL检查
String trackingno = "";
if(trackingNumberText.getText().length() > 0)
{
trackingno = trackingNumberText.getText().toString();
} else {
Toast.makeText(getApplicationContext(), "Enter values", Toast.LENGTH_LONG).show();
return;
}
修改
您必须在后台线程中将所有请求发送到服务器，使用AsyncTask