我想将JSON数组中的数据插入到SQLite数据库中。我创建了两个类CategoryHelper.java和AndroidJSONParsingActivity.java来获取java响应。当我运行代码时，在databaseHelper.saveCategoryRecord(id,name);我的API工作正常，并向我提供数据。
我的代码如下：
CategoryHelper.java
package com.androidhive.jsonparsing;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class CategoryHelper {
private static final int DATABASE_VERSION = 2;
private static final String DATABASE_NAME = "category.db";
private static final String TABLE_NAME = "tbcategory";
public static final String CATEGORY_COLUMN_ID = "_id";
public static final String CATEGORY_COLUMN_NAME = "name";
Category openHelper;
private SQLiteDatabase database;
public CategoryHelper(Context context){
openHelper = new Category(context);
database = openHelper.getWritableDatabase();
}
public void saveCategoryRecord(String id, String name) {
ContentValues contentValues = new ContentValues();
contentValues.put(CATEGORY_COLUMN_ID, id);
contentValues.put(CATEGORY_COLUMN_NAME, name);
database.insert(TABLE_NAME, null, contentValues);
}
public Cursor getTimeRecordList() {
return database.rawQuery("select * from " + TABLE_NAME, null);
}
private class Category extends SQLiteOpenHelper {
public Category(Context context) {
// TODO Auto-generated constructor stub
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL("CREATE TABLE " + TABLE_NAME + "( "
+ CATEGORY_COLUMN_ID + " INTEGER PRIMARY KEY, "
+ CATEGORY_COLUMN_NAME + " TEXT )" );
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS"+ TABLE_NAME);
onCreate(db);
}
}
}
AndroidJSONParsingActivity.java
package com.androidhive.jsonparsing;
import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
public class AndroidJSONParsingActivity extends ListActivity {
// url to make request
private static String url="API TO GET THE DATA";
// JSON Node names
private static final String TAG_CATEGORY = "categories";
private static final String TAG_CATEGORY_ID = "category_id";
private static final String TAG_NAME = "name";
private static final String TAG_IS_ACTIVE = "is_active";
// contacts JSONArray
JSONArray contacts = null;
private CategoryHelper databaseHelper;
//private SQLiteDatabase mydatabase = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Hashmap for ListView
ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>();
// Creating JSON Parser instance
JSONParser jParser = new JSONParser();
// getting JSON string from URL
JSONObject json = jParser.getJSONFromUrl(url);
try {
// Getting Array of Contacts
contacts = json.getJSONArray(TAG_CATEGORY);
// looping through All Contacts
for(int i = 0; i < contacts.length(); i++){
JSONObject c = contacts.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_CATEGORY_ID);
String name = c.getString(TAG_NAME);
String is_active = c.getString(TAG_IS_ACTIVE);
databaseHelper.saveCategoryRecord(id,name);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_CATEGORY_ID, id);
map.put(TAG_NAME, name);
map.put(TAG_IS_ACTIVE, is_active);
// adding HashList to ArrayList
contactList.add(map);
}
} catch (JSONException e) {
e.printStackTrace();
}
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(this, contactList,
R.layout.list_item,
new String[] { TAG_NAME, TAG_IS_ACTIVE, TAG_CATEGORY_ID }, new int[] {
R.id.name, R.id.email, R.id.mobile });
setListAdapter(adapter);
// selecting single ListView item
ListView lv = getListView();
// Launching new screen on Selecting Single ListItem
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String name = ((TextView) view.findViewById(R.id.name)).getText().toString();
String cost = ((TextView) view.findViewById(R.id.email)).getText().toString();
String description = ((TextView) view.findViewById(R.id.mobile)).getText().toString();
// Starting new intent
Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class);
in.putExtra(TAG_NAME, name);
in.putExtra(TAG_IS_ACTIVE, cost);
in.putExtra(TAG_CATEGORY_ID, description);
startActivity(in);
}
});
}
}
logcat的：
01-21 20:13:49.226: E/AndroidRuntime(301): FATAL EXCEPTION: main
01-21 20:13:49.226: E/AndroidRuntime(301): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.androidhive.jsonparsing/com.androidhive.jsonparsing.AndroidJSONParsingActivity}: java.lang.NullPointerException
01-21 20:13:49.226: E/AndroidRuntime(301): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
01-21 20:13:49.226: E/AndroidRuntime(301): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
01-21 20:13:49.226: E/AndroidRuntime(301): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-21 20:13:49.226: E/AndroidRuntime(301): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-21 20:13:49.226: E/AndroidRuntime(301): at android.os.Handler.dispatchMessage(Handler.java:99)
01-21 20:13:49.226: E/AndroidRuntime(301): at android.os.Looper.loop(Looper.java:123)
01-21 20:13:49.226: E/AndroidRuntime(301): at android.app.ActivityThread.main(ActivityThread.java:4627)
01-21 20:13:49.226: E/AndroidRuntime(301): at java.lang.reflect.Method.invokeNative(Native Method)
01-21 20:13:49.226: E/AndroidRuntime(301): at java.lang.reflect.Method.invoke(Method.java:521)
01-21 20:13:49.226: E/AndroidRuntime(301): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-21 20:13:49.226: E/AndroidRuntime(301): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-21 20:13:49.226: E/AndroidRuntime(301): at dalvik.system.NativeStart.main(Native Method)
01-21 20:13:49.226: E/AndroidRuntime(301): Caused by: java.lang.NullPointerException
01-21 20:13:49.226: E/AndroidRuntime(301): at com.androidhive.jsonparsing.AndroidJSONParsingActivity.onCreate(AndroidJSONParsingActivity.java:65)
01-21 20:13:49.226: E/AndroidRuntime(301): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-21 20:13:49.226: E/AndroidRuntime(301): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
请指导我如何将JSON数组数据插入数据库或我做错了。每一个回应都是可观的。
答案 0 :(得分：13)
在使用之前，您忘记在databaseHelper的Activity中初始化oncreate对象。
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
databaseHelper=new CategoryHelper(AndroidJSONParsingActivity.this);
//your code here..........
答案 1 :(得分：5)
您永远不会实例化databaseHelper。您无法在null对象上调用方法。
答案 2 :(得分：4)
你还有一个小问题：
db.execSQL("DROP TABLE IF EXISTS"+ TABLE_NAME);
EXISTS之后你忘记了空格。它应该是这样的：
db.execSQL("DROP TABLE IF EXISTS "+ TABLE_NAME);