5
Tôi đang gặp sự cố khi lưu trữ dữ liệu JSON vào sqlite. Đây là mã mà tôi đang cố gắng triển khai ngay bây giờ. Dữ liệu JSON không phải là đặc biệt lớn với chỉ có 40 dòng trong đó.Cách lưu trữ JSON trong SQLite
Các hoạt động chính là:
public class DatabaseActivity extends Activity {
/** Called when the activity is first created. */
public DBAdapter
DBAdapter =new DBAdapter(this);
TextView txt;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Create a crude view - this should really be set via the layout resources
// but since its an example saves declaring them in the XML.
LinearLayout rootLayout = new LinearLayout(getApplicationContext());
txt = new TextView(getApplicationContext());
rootLayout.addView(txt);
setContentView(rootLayout);
// Set the text and call the connect function.
txt.setText("Connecting...");
//call the method to run the data retreival
txt.setText(getServerData(KEY_13));
}
public static final String KEY_13 = "http://xxx.xxx.xxx/api/train.php";
private String getServerData(String returnString) {
InputStream is = null;
String result = "";
//the train line to send
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("code","A"));
//http post
try{
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(KEY_13);
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}catch(Exception e){
Log.e("log_tag", "Error in http connection "+e.toString());
}
//convert response to string
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();
result=sb.toString();
}catch(Exception e){
Log.e("log_tag", "Error converting result "+e.toString());
}
//parse json data
try{
JSONArray jArray = new JSONArray(result);
for(int i=0;i<jArray.length();i++){
JSONObject json_data = jArray.getJSONObject(i);
DBAdapter.insertTrain(json_data.getString("id"),
json_data.getString("code"),
json_data.getString("station"),
json_data.getString("platform"),
json_data.getString("timetillstation"),
json_data.getString("traindestination"),
//Get an output to the screen
returnString += "\n\t" + jArray.getJSONObject(i);
}
}catch(JSONException e){
Log.e("log_tag", "Error parsing data "+e.toString());
}
return returnString;
}
}
Các bộ chuyển đổi là:
public class DBAdapter{
public static final String KEY_ID = "id";
public static final String KEY_Code = "code";
public static final String KEY_Station = "station";
public static final String KEY_Platform = "platform";
public static final String KEY_TimeTillStation = "timetillstation";
public static final String KEY_TrainDestination = "traindestination";
private static final String TAG = "DBAdapter";
private static final String DATABASE_NAME = "trains";
private static final String DATABASE_TABLE = "Mekerel";
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_CREATE =
"create table titles (id integer primary key, "
+ "code text not null,"
+ "station text not null,"
+ "platform text not null,"
+ "timetillstation text not null,"
+ "traindestination text not null);";
private final Context context;
private DatabaseHelper DBHelper;
private SQLiteDatabase db;
public DBAdapter(Context ctx)
{
this.context = ctx;
DBHelper = new DatabaseHelper(context);
this.db=DBHelper.getWritableDatabase();
}
private static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db)
{
db.execSQL(DATABASE_CREATE); }
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion)
{
Log.w(TAG, "Upgrading database from version " + oldVersion
+ " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS titles");
onCreate(db);
}
}
//---opens the database---
public DBAdapter open() throws SQLException
{
db = DBHelper.getWritableDatabase();
return this;
}
//---closes the database---
public void close()
{
DBHelper.close();
}
//---insert a train into the database---
public long insertTrain(String id, String code, String station, String platform, String timetillstation, String traindestination)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_ID, id);
initialValues.put(KEY_Code, code);
initialValues.put(KEY_Station, station);
initialValues.put(KEY_Platform, platform);
initialValues.put(KEY_TimeTillStation, timetillstation);
initialValues.put(KEY_TrainDestination, traindestination);
return db.insert(DATABASE_TABLE, null, initialValues);
}
//---retrieves all the ttrain---
public Cursor getAllTrains()
{
return db.query(DATABASE_TABLE, new String[] {
KEY_ID,
KEY_Code,
KEY_Station,
KEY_Platform,
KEY_TimeTillStation,
KEY_TrainDestination},
null,
null,
null,
null,
null,
null);
}
//---retrieves a particular train---
public Cursor getTrain(long id) throws SQLException
{
Cursor mCursor =
db.query(true, DATABASE_TABLE, new String[] {
KEY_ID,
KEY_Code,
KEY_Station,
KEY_Platform,
KEY_TimeTillStation,
KEY_TrainDestination},
KEY_ID + "=" + id,
null,
null,
null,
null,
null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
//---updates a train---
public boolean updateTrain(long id, String code, String station, String platform, String timetillstation, String traindestination)
{
ContentValues args = new ContentValues();
args.put(KEY_Code, code);
args.put(KEY_Station, station);
args.put(KEY_Platform, platform);
args.put(KEY_TimeTillStation, timetillstation);
args.put(KEY_TrainDestination, traindestination);
return db.update(DATABASE_TABLE, args,
KEY_ID + "=" + id, null) > 0;
}
}
Tôi không chắc chắn nơi để đi từ đây như vẫn còn có những vấn đề. Con mèo đăng nhập hiển thị như sau:
12-04 12:43:09.691: E/AndroidRuntime(21334): FATAL EXCEPTION: main
12-04 12:43:09.691: E/AndroidRuntime(21334): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{ta.dabase/ta.dabase.DatabaseActivity}: java.lang.NullPointerException
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1680)
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1784)
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.app.ActivityThread.access$1500(ActivityThread.java:123)
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:939)
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.os.Handler.dispatchMessage(Handler.java:99)
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.os.Looper.loop(Looper.java:130)
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.app.ActivityThread.main(ActivityThread.java:3835)
12-04 12:43:09.691: E/AndroidRuntime(21334): at java.lang.reflect.Method.invokeNative(Native Method)
12-04 12:43:09.691: E/AndroidRuntime(21334): at java.lang.reflect.Method.invoke(Method.java:507)
12-04 12:43:09.691: E/AndroidRuntime(21334): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:847)
12-04 12:43:09.691: E/AndroidRuntime(21334): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
12-04 12:43:09.691: E/AndroidRuntime(21334): at dalvik.system.NativeStart.main(Native Method)
12-04 12:43:09.691: E/AndroidRuntime(21334): Caused by: java.lang.NullPointerException
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:118)
12-04 12:43:09.691: E/AndroidRuntime(21334): at ta.dabase.DBAdapter.<init>(DBAdapter.java:43)
12-04 12:43:09.691: E/AndroidRuntime(21334): at ta.dabase.DatabaseActivity.<init>(DatabaseActivity.java:32)
12-04 12:43:09.691: E/AndroidRuntime(21334): at java.lang.Class.newInstanceImpl(Native Method)
12-04 12:43:09.691: E/AndroidRuntime(21334): at java.lang.Class.newInstance(Class.java:1409)
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
12-04 12:43:09.691: E/AndroidRuntime(21334): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1672)
12-04 12:43:09.691: E/AndroidRuntime(21334): ... 11 more
Cuối cùng, tôi tự hỏi liệu có ai có thể đặt mã đăng nhập thích hợp để phát hiện mã nào sai không? Cảm ơn
bạn đã kiểm tra xem cơ sở dữ liệu của mình đã được tạo chưa? – Rakhita
@Rakhita Làm cách nào để tôi thực hiện việc này khi ứng dụng mở nhưng không hoạt động? – Hellboundz
@Rakhita Nó dường như không tạo ra một cơ sở dữ liệu. Bạn có biết tôi có thể làm gì không? – Hellboundz