我试图在Android上用JSON和php / mysql上的HTTP请求来显示mysql数据库中的一些数据。
应用程序只需按一个按钮，它将在日志cat中显示数据库中的选定数据，并使用intent在模拟器上显示第二页。
问题是，当我尝试运行应用程序时，系统会在将请求发送到http之前进行压缩，并且我使用localhost服务器（wamp），因此我使用的URL是：http：// 10.0。 2.2 / studentservice / StudentService / getStudentByID.php
按下按钮后，这是
10-15 14:07:28.160: I/dalvikvm(854): threadid=3: reacting to signal 3
10-15 14:07:28.320: I/dalvikvm(854): Wrote stack traces to '/data/anr/traces.txt'
10-15 14:07:28.630: D/gralloc_goldfish(854): Emulator without GPU emulation detected.
10-15 14:07:28.660: I/dalvikvm(854): threadid=3: reacting to signal 3
10-15 14:07:28.670: I/dalvikvm(854): Wrote stack traces to '/data/anr/traces.txt'
10-15 14:07:35.800: E/Error befor http(854): Error before the http request
10-15 14:07:36.210: I/dalvikvm(854): threadid=3: reacting to signal 3
10-15 14:07:36.230: I/dalvikvm(854): Wrote stack traces to '/data/anr/traces.txt'
10-15 14:07:36.730: I/dalvikvm(854): threadid=3: reacting to signal 3
10-15 14:07:36.750: I/dalvikvm(854): Wrote stack traces to '/data/anr/traces.txt'
10-15 14:07:37.250: I/dalvikvm(854): threadid=3: reacting to signal 3
10-15 14:07:37.270: I/dalvikvm(854): Wrote stack traces to '/data/anr/traces.txt'
10-15 14:07:37.770: I/dalvikvm(854): threadid=3: reacting to signal 3
10-15 14:07:37.780: I/dalvikvm(854): Wrote stack traces to '/data/anr/traces.txt'
10-15 14:07:38.281: I/dalvikvm(854): threadid=3: reacting to signal 3
10-15 14:07:38.300: I/dalvikvm(854): Wrote stack traces to '/data/anr/traces.txt'
10-15 14:07:38.800: I/dalvikvm(854): threadid=3: reacting to signal 3
10-15 14:07:38.821: I/dalvikvm(854): Wrote stack traces to '/data/anr/traces.txt'
10-15 14:07:48.400: I/dalvikvm(854): threadid=3: reacting to signal 3
10-15 14:07:48.460: I/dalvikvm(854): Wrote stack traces to '/data/anr/traces.txt'
10-15 14:10:25.630: I/dalvikvm(854): threadid=3: reacting to signal 3
10-15 14:10:25.650: I/dalvikvm(854): Wrote stack traces to '/data/anr/traces.txt'
10-15 14:35:13.781: E/AndroidRuntime(906): FATAL EXCEPTION: main
10-15 14:35:13.781: E/AndroidRuntime(906): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lebdev.fitguide.activities/com.lebdev.fitguide.activities.SecondaryActivity}: java.lang.NullPointerException: println needs a message
10-15 14:35:13.781: E/AndroidRuntime(906): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
10-15 14:35:13.781: E/AndroidRuntime(906): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
10-15 14:35:13.781: E/AndroidRuntime(906): at android.app.ActivityThread.access$600(ActivityThread.java:123)
10-15 14:35:13.781: E/AndroidRuntime(906): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
10-15 14:35:13.781: E/AndroidRuntime(906): at android.os.Handler.dispatchMessage(Handler.java:99)
10-15 14:35:13.781: E/AndroidRuntime(906): at android.os.Looper.loop(Looper.java:137)
10-15 14:35:13.781: E/AndroidRuntime(906): at android.app.ActivityThread.main(ActivityThread.java:4424)
10-15 14:35:13.781: E/AndroidRuntime(906): at java.lang.reflect.Method.invokeNative(Native Method)
10-15 14:35:13.781: E/AndroidRuntime(906): at java.lang.reflect.Method.invoke(Method.java:511)
10-15 14:35:13.781: E/AndroidRuntime(906): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
10-15 14:35:13.781: E/AndroidRuntime(906): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
10-15 14:35:13.781: E/AndroidRuntime(906): at dalvik.system.NativeStart.main(Native Method)
10-15 14:35:13.781: E/AndroidRuntime(906): Caused by: java.lang.NullPointerException: println needs a message
10-15 14:35:13.781: E/AndroidRuntime(906): at android.util.Log.println_native(Native Method)
10-15 14:35:13.781: E/AndroidRuntime(906): at android.util.Log.e(Log.java:231)
10-15 14:35:13.781: E/AndroidRuntime(906): at com.lebdev.fitguide.controller.HttpManager.getResponseFromURL(HttpManager.java:70)
10-15 14:35:13.781: E/AndroidRuntime(906): at com.lebdev.fitguide.activities.SecondaryActivity.onCreate(SecondaryActivity.java:54)
10-15 14:35:13.781: E/AndroidRuntime(906): at android.app.Activity.performCreate(Activity.java:4465)
10-15 14:35:13.781: E/AndroidRuntime(906): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
10-15 14:35:13.781: E/AndroidRuntime(906): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
10-15 14:35:13.781: E/AndroidRuntime(906): ... 11 more
10-15 14:35:14.341: I/dalvikvm(906): threadid=3: reacting to signal 3
10-15 14:35:14.370: I/dalvikvm(906): Wrote stack traces to '/data/anr/traces.txt'
package com.lebdev.fitguide.activities;
import com.lebdev.fitguide.businessModel.Student;
import com.lebdev.fitguide.businessModel.Subject;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
EditText txtMessage;
TextView lblMessage;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txtMessage = (EditText) findViewById(R.id.txtMessage);
lblMessage = (TextView) findViewById(R.id.lblMessage);
}
@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;
}
public void Onclick_btnSend(View v) {
Intent intent = new Intent(this, SecondaryActivity.class);
//intent.putExtra("message", txtMessage.getText().toString());
Student std = new Student(txtMessage.getText().toString(),1234, 1);
std.getSubjects().add(new Subject("itc", 5));
intent.putExtra("Student", std);
startActivity(intent);
Toast.makeText(this, "i am sending a message here", Toast.LENGTH_SHORT).show();
}
}
package com.lebdev.fitguide.om;
import java.util.ArrayList;
import java.util.List;
import org.json.JSONObject;
import android.util.Log;
import com.lebdev.fitguide.businessModel.Student;
public class JsonObjectMapper {
public static Student jsonToStudent(JSONObject jsonObject) {
Student std = null;
try {
std = new Student(jsonObject.getJSONArray("Student")
.getJSONObject(0).getString("Name"),
Integer.parseInt(jsonObject.getJSONArray("Student")
.getJSONObject(0).getString("index")),
Integer.parseInt(jsonObject.getJSONArray("Student")
.getJSONObject(0).getString("ID")));
} catch (Exception ex) {
Log.e("Error Json Converter", ex.getMessage());
}
return std;
}
public static List<Student> jsonToStudentList(JSONObject jsonObject) {
List<Student> stdList = new ArrayList<Student>();
try {
for (int i = 0; i < jsonObject.getJSONArray("Student").length(); i++) {
stdList.add(new Student(jsonObject.getJSONArray("Student")
.getJSONObject(i).getString("Name"), Integer
.parseInt(jsonObject.getJSONArray("Student")
.getJSONObject(i).getString("index")), Integer
.parseInt(jsonObject.getJSONArray("Student")
.getJSONObject(i).getString("ID"))));
}
} catch (Exception ex) {
Log.e("Error Json Converter", ex.getMessage());
}
return stdList;
}
}
package com.lebdev.fitguide.activities;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONObject;
import com.lebdev.fitguide.businessModel.Student;
import com.lebdev.fitguide.controller.HttpManager;
import com.lebdev.fitguide.controller.JSONParser;
import com.lebdev.fitguide.om.JsonObjectMapper;
import android.app.Activity;
import android.os.Bundle;
import android.os.StrictMode;
import android.util.Log;
import android.view.Menu;
import android.widget.TextView;
import android.widget.Toast;
public class SecondaryActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_secondary);
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder()
.permitAll().build();
StrictMode.setThreadPolicy(policy);
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("sid", "2"));
Log.e("Error befor http", "Error before the http request");
JSONObject jsonObj = JSONParser
.parseJSONFromString(new HttpManager()
.getResponseFromURL(
"http://10.0.2.2/studentservice/StudentService/getStudentByID.php",
params));
Log.e("Error after http", "Error after the http request");
Student std = JsonObjectMapper.jsonToStudent(jsonObj);
Log.e("STUDENT DATA", "ID:" + std.getID() + "Name:" + std.getName()
+ "Index: " + std.getIndex());
/*
Bundle bundle = getIntent().getExtras();
if (bundle != null) {
TextView lblMessage = (TextView) findViewById(R.id.lblSentMessage);
Student student = bundle.getParcelable("Student");
lblMessage.setText("I 've recieved a student with a name "
+ student.getName() + " and has a Subject "
+ student.getSubjects().get(0).getName() + " with a grade "
+ student.getSubjects().get(0).getGrade());
}
*/
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.secondary, menu);
return true;
}
}
答案 0 :(得分：0)
10-15 14:35:13.781: E/AndroidRuntime(906): at com.lebdev.fitguide.controller.HttpManager.getResponseFromURL(HttpManager.java:70)
这是一个指向代码，行号和所有内容的指针，指向空指针（Log.e（）的空消息）来自哪里并导致崩溃。
从你的logcat中可以看出这一点，所以你在
中做了些什么 JSONObject jsonObj = JSONParser
.parseJSONFromString(new HttpManager()
.getResponseFromURL(
"http://10.0.2.2/studentservice/StudentService/getStudentByID.php",
params));
这导致写入Log.e（）的空信息。