Develop Reference

Pass LinkedList to another activity

I have a Linked List in one activity (A) that I want to share with another Activity (B).
The list contains a username of type string and contains coordinates of type LatLng. I am also using Intent and bundle to share data between activities. I tried using Parcelable but unable to figure out how to use it. Here is the code I have:
data.java
public class data implements Parcelable{
private LatLng coordinates;
private String name;
public data() {
name = null;
coordinates = null;
}
public data(String name, LatLng coordinates)
{
this.name = name;
this.coordinates = coordinates;
}
public data(Parcel in) {
coordinates = in.readParcelable(LatLng.class.getClassLoader());
name = in.readString();
}
public static final Creator<data> CREATOR = new Creator<data>() {
#Override
public data createFromParcel(Parcel in) {
return new data(in);
}
#Override
public data[] newArray(int size) {
return new data[size];
}
};
public LatLng getLatLng () {
return coordinates;
}
#Override
public int describeContents() {
return hashCode();
}
#Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(name);
dest.writeParcelable(coordinates, flags);
}
}
Activity A
public class A extends FragmentActivity implements
OnMapReadyCallback,
GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener,
GoogleMap.OnMyLocationButtonClickListener,
ActivityCompat.OnRequestPermissionsResultCallback {
Button switchToSeek;
double mLatitude;
double mLongitude;
LinkedList<data> storedData = new LinkedList<>();
protected void onCreate(Bundle savedInstanceState) {
...
switchToSeek.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
getCurrentLocation();
Intent intent = new Intent(A.this, B.class);
Bundle xy = new Bundle();
xy.putDouble("x", mLatitude);
xy.putDouble("y", mLongitude);
xy.putParcelable("list", storedData); <---------- error: wrong second arugment
intent.putExtra("xy", xy);
A.this.startActivity(intent);
}
});
Activity B
public class B extends FragmentActivity implements OnMapReadyCallback {
double mLatitude;
double mLongitude;
LatLng current;
GoogleMap gMap;
LinkedList <data> copyData = new LinkedList<>();
#Override
public void onMapReady(GoogleMap googleMap) {
gMap = googleMap;
...
Intent intent = getIntent();
Bundle xy = intent.getBundleExtra("xy");
if (xy != null) {
mLatitude = xy.getDouble("x");
mLongitude = xy.getDouble("y");
}
/***** Call linked list here and set equal to copyData *****/
current = new LatLng(mLatitude, mLongitude);
gMap.moveCamera(CameraUpdateFactory.newLatLngZoom(current, 18.0f));
}

There is no easy way to do that, since LinkedList does not implement serializable or parcelable.
You CAN implement your own linked list class and make it a serializable/parcelable object which can then be passed.
Or you can convert its content into another data type such as an array and then recreate the linkedlist.* THIS IS HIGHLY INEFFICIENT
I believe there are other ways but this is a standard problem in android dev. Maybe try using fragments if possible and passing the linkedlist through a setter()

If the list is not huge, you can do it using the following helper class:
public class ParcelableLinkedList<E extends Parcelable> implements Parcelable {
private final LinkedList<E> linkedList;
public final Creator<ParcelableLinkedList> CREATOR = new Creator<ParcelableLinkedList>() {
#Override
public ParcelableLinkedList createFromParcel(Parcel in) {
return new ParcelableLinkedList(in);
}
#Override
public ParcelableLinkedList[] newArray(int size) {
return new ParcelableLinkedList[size];
}
};
public ParcelableLinkedList(Parcel in) {
// Read size of list
int size = in.readInt();
// Read the list
linkedList = new LinkedList<E>();
for (int i = 0; i < size; i++) {
linkedList.add((E)in.readParcelable(ParcelableLinkedList.class.getClassLoader()));
}
}
public ParcelableLinkedList(LinkedList<E> linkedList) {
this.linkedList = linkedList;
}
LinkedList<E> getLinkedList() {
return linkedList;
}
#Override
public int describeContents() {
return 0;
}
#Override
public void writeToParcel(Parcel parcel, int flags) {
// Write size of the list
parcel.writeInt(linkedList.size());
// Write the list
for (E entry : linkedList) {
parcel.writeParcelable(entry, flags);
}
}
}
In your onClick() method, add the data to the Bundle like this:
xy.putParcelable("list", new ParcelableLinkedList<data>(storedData));
To extract the data from the Bundle, do this:
copyData = ((ParcelableLinkedList<data>)xy.getParcelable("list")).getLinkedList();
I haven't actually compiled and tested this code, but it should work.
If the list is really huge, you are better off storing it in a static member variable in one class and then just referencing it from the other. This isn't normally the way you want to do things in Android, but it is sometimes more expedient to do this than to serialize and deserialize a huge amount of data just to pass it between 2 activities that have access to the same memory space.

Adding a RealmObject to a RealmList in Android

I am currently trying to add a RealmObject to RealmList inside another RealmObject.
So this is the way I am doing it at the moment.
First I create and save a RealmObject called "RouteRealm" like this:
public void insertNewRoute(int routeId, long routeDate) {
realm.beginTransaction();
RouteRealm routeRealm = realm.createObject(RouteRealm.class);
routeRealm.setId(routeId);
routeRealm.setDate(routeDate);
realm.commitTransaction();
}
The class RealmObject looks like this:
public class RouteRealm extends RealmObject {
#PrimaryKey
private int id;
private long date;
private RealmList<RoutePointRealm> routePoints;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public long getDate() {
return date;
}
public void setDate(long date) {
this.date = date;
}
public RealmList<RoutePointRealm> getRoutePoints() {
return routePoints;
}
public void setRoutePoints(RealmList<RoutePointRealm> routePoints) {
this.routePoints = routePoints;
}
}
The above works. The problem occurs when I try to add a RoutePointRealm to the list called routePoints. Here is my code for adding the RoutePointRealm object to the list:
public void insertNewRoutePoint(int routeId, String address, float latitude, float longitude, long routePointId, long routePointTime) {
realm.beginTransaction();
RouteRealm routeRealm = realm.where(RouteRealm.class).equalTo("id", routeId).findFirst();
RoutePointRealm routePointRealm = realm.createObject(RoutePointRealm.class);
routePointRealm.setAddress(address);
routePointRealm.setLatitude(latitude);
routePointRealm.setLongitude(longitude);
routePointRealm.setRoutePointID(routePointId);
routePointRealm.setRoutepointTime(routePointTime);
routeRealm.getRoutePoints().add(routePointRealm);
realm.copyToRealmOrUpdate(routeRealm);
realm.commitTransaction();
}
And the RoutePointRealm looks like this:
public class RoutePointRealm extends RealmObject {
#PrimaryKey
private long routePointID;
private float longitude, latitude;
private long routepointTime;
private String address;
public long getRoutePointID() {
return routePointID;
}
public void setRoutePointID(long routePointID) {
this.routePointID = routePointID;
}
public float getLongitude() {
return longitude;
}
public void setLongitude(float longitude) {
this.longitude = longitude;
}
public float getLatitude() {
return latitude;
}
public void setLatitude(float latitude) {
this.latitude = latitude;
}
public long getRoutepointTime() {
return routepointTime;
}
public void setRoutepointTime(long routepointTime) {
this.routepointTime = routepointTime;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}
For some reason, the RoutePointRealm are added to the list, but all of its fields are set to zero and null. I have debugged my app to make sure that all of the parameters contains the correct values with the right datatypes etc. So now I know that the problem is related to the Realm methods.
What am I doing wrong?

First of all, thank you for your answers! I still couldn't get it to work after changing the solutions you've proposed. At least I didn't think so.
The reason I thought it didn't work, was partly because of a mistake that I made with my gui showing a zero value.. This made me to go into debugging the app, but apparently the debugger always shows zero or null values for the Realm objects.. At least in my case.
So at last, I tried making a Toast message with a fetched value from Realm and it returned what it was supposed to.
So I don't think that there were any problems to begin with.. The debugger just got me thinking so. I am sorry if I wasted your time, but I still thought that I should post this as an answer if other were to encounter the same problem.

All your objects are managed by Realm, so you don't need the realm.copyToRealmOrUpdate(routeRealm); call.

the problem comes from ID, Realm not support auto increment behaviour so you should do it manually.
something like :
beginTransaction()
foo.setId(value)
commitTrasaction()

My personal recommendation:
public void insertNewRoute(final int routeId, final long routeDate) {
final RouteRealm routeRealm = new RouteRealm();
realm.executeTransaction(new Realm.Transaction() {
#Override
public void execute(Realm realm) {
routeRealm.setId(routeId);
routeRealm.setDate(routeDate);
realm.insertOrUpdate(routeRealm);
}
});
}
public void insertNewRoutePoint(final int routeId, final String address, final float latitude,
final float longitude, final long routePointId, final long routePointTime) {
realm.executeTransaction(new Realm.Transaction() {
#Override
public void execute(Realm realm) {
RouteRealm routeRealm = realm.where(RouteRealm.class).equalTo(RouteRealmFields.ID, routeId).findFirst();
RoutePointRealm routePointRealm = new RoutePointRealm();
routePointRealm.setAddress(address);
routePointRealm.setLatitude(latitude);
routePointRealm.setLongitude(longitude);
routePointRealm.setRoutePointID(routePointId);
routePointRealm.setRoutepointTime(routePointTime);
routePointRealm = realm.copyToRealmOrUpdate(routePointRealm);
routeRealm.getRoutePoints().add(routePointRealm);
}
});
}

What is the difference between `writeValue` and `writeParcelable`?

I have been searching for a way to pass an object from one Activity to another.
Different tutorials stated that the best way to do it is to make the class Parcelable. I've managed to implement it, but I have one question left.
There is a reference to another parcelable object (location) inside the Office class. This tutorial tells to serialize it using dest.writeParcelable(location, flags); and in.readParcelable(LatLng.class.getClassLoader());, but the parcelabler created the code with dest.writeValue(location); and then (LatLng) in.readValue(LatLng.class.getClassLoader());.
I have checked and it worked both ways.
Could somebody please explain what is the difference between these two approaches? Is any of them better for some reasons? Thank you!
public class Office implements Parcelable {
#SuppressWarnings("unused")
public static final Parcelable.Creator<Office> CREATOR = new Parcelable.Creator<Office>() {
#Override
public Office createFromParcel(Parcel in) {
return new Office(in);
}
#Override
public Office[] newArray(int size) {
return new Office[size];
}
};
public final String name;
public final String address;
public final LatLng location;
public Office(String name, String address, LatLng location) {
this.name = name;
this.address = address;
this.location = location;
}
protected Office(Parcel in) {
name = in.readString();
address = in.readString();
// location = (LatLng) in.readValue(LatLng.class.getClassLoader());
location = in.readParcelable(LatLng.class.getClassLoader());
}
#Override
public int describeContents() {
return 0;
}
#Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(name);
dest.writeString(address);
// dest.writeValue(location);
dest.writeParcelable(location, flags);
}
}

writeValue is more generic, and since it takes an Object as parameter, internally they check the instanceOf the object to call the specific method. If you know the type, I would stick with using the specific one

Difference between storing data in shared preferences and database in android

I am creating an application in android and I want to store data of places user selected on the google map. I am currently storing all the places by adding them all in an array and then serialize them by Gson library and it works fine and coding is very simple and easy but if i use data base instead of that that then the coding will be more complex and because implantation of data base is more complex then simply string the array of places to shared preferences. below is the class whose objects are i am storing and saving in the shared preferences but if want to store them on the data base then i have to go through more complex I have to create queries for insert, delete update etc. so suggest me that should i use db or shred preference is good for saving list of places.
package com.example.googlemapstext;
import java.util.ArrayList;
import android.location.Address;
public class MyPlace {
private int id;
private String placeName;
private Address placeAddress;
private int ringerState;
private int brightnessState;
private int wifiState;
private int gpsState;
private int bluetoothState;
private int radiusValueIndex;
private ArrayList<Contact> contactArrayList;
private String message;
private double radiusValue;
private boolean notificationCheck;
public MyPlace(int id,String placeName, Address placeAddress, String radiusValue,
int ringerState, int brightnessState, int wifiState, int gpsState,
int bluetoothState, int radiusValueIndex, ArrayList<Contact> contactArrayList,
String message, boolean notificationCheck) {
this.id=id;
this.placeName = placeName;
this.placeAddress = placeAddress;
this.radiusValue = getTrimedRadiusValue(radiusValue);
this.ringerState = ringerState;
this.brightnessState = brightnessState;
this.wifiState = wifiState;
this.gpsState = gpsState;
this.bluetoothState = bluetoothState;
this.contactArrayList = contactArrayList;
this.message = message;
this.radiusValueIndex = radiusValueIndex;
this.notificationCheck = notificationCheck;
}
private double getTrimedRadiusValue(String radiusValue)
{
radiusValue=radiusValue.replace("Radius ", "");
radiusValue=radiusValue.replace(" Meters", "");
return Double.parseDouble(radiusValue);
}
public boolean getNotificationCheck() {
return notificationCheck;
}
public void setNotificationCheck(boolean notificationCheck) {
this.notificationCheck = notificationCheck;
}
public int getRadiusValueIndex() {
return radiusValueIndex;
}
public void setRadiusValueIndex(int radiusValueIndex) {
this.radiusValueIndex = radiusValueIndex;
}
public int getRingerState() {
return ringerState;
}
public void setRingerState(int ringerState) {
this.ringerState = ringerState;
}
public int getBrightnessState() {
return brightnessState;
}
public void setBrightnessState(int brightnessState) {
this.brightnessState = brightnessState;
}
public int getWifiState() {
return wifiState;
}
public void setWifiState(int wifiState) {
this.wifiState = wifiState;
}
public int getGpsState() {
return gpsState;
}
public void setGpsState(int gpsState) {
this.gpsState = gpsState;
}
public int getBluetoothState() {
return bluetoothState;
}
public void setBluetoothState(int bluetoothState) {
this.bluetoothState = bluetoothState;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
public double getRadiusValue() {
return radiusValue;
}
public void setRadiusValue(String radiusValue) {
this.radiusValue = getTrimedRadiusValue(radiusValue);
}
public String getPlaceName() {
return placeName;
}
public void setPlaceName(String placeName) {
this.placeName = placeName;
}
public Address getPlaceAddress() {
return placeAddress;
}
public void setPlaceAddress(Address placeAddress) {
this.placeAddress = placeAddress;
}
public ArrayList<Contact> getContactArrayList() {
return contactArrayList;
}
public void setContactArrayList(ArrayList<Contact> contactArrayList) {
this.contactArrayList = contactArrayList;
}
public int getId() {
return id`enter code here`;
}
public void setId(int id) {
this.id = id;
}
}

The main difference between SharedPreferences and DataBase is like you mentioned :
SharedPreferences works on an Key-Value pair basis. you simply provide the Key and get back the Value you stored. that's great.
DataBase creates an SQLite Tables and you need to use queries to pull them out.
I think that if you are good with the JSON mechanism that you built, then storing a string in SharedPreferences is all you need.
But when the Data get more and more complex, and you would like quick access to any part of it, I think DB would be easier than parsing and seaching a JSON string all the time.
Yes, it might make you write more code for handling the DB queries..

I think SQLite will be better for you. I only use SharePreferences for small, simple and "key - value" structured data. (and it should be like that)
You have a lot of data, so SQLite is the way to go.
Read this for more information : Pros and Cons of SQLite and Shared Preferences

I think answer depends on how many places you want to save and what do you plan to do with them but I consider DB as hte best way to go.
With a DB you will be able to create queries to get only places you want and not load all places in a list and search in it.
To simplify DB creation (and use) you can try orm for Android like OrmLite and GreenDao. I think OrmLite is easier to use than GreenDao (but second one seems to have better performance...) and you can find multiple examples there.
In my opinion, SharedPreferences should only be used for saving user preferences data.

Save custom objects when activty stops on Android

I've written a small andorid app. This app uses a vector of custom objects and displays them in a listview. I want to save those objects when the activity is send to background. What is the best way for this. In the vector are about 25 objects. Every object has a boolean, two long, and two strings.
Thanks for your help

do you need them saved when the app shuts down or just when the activity goes into the background?
if your objects are parcelables you could use the save and restore instance state methods:
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putParcelableArrayList("objectsArray", myObjects); // if its an array of parceleble objects
}
#Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
myObjects= savedInstanceState.getParcelableArrayList("objectsArray");
}
here is an example of a parcelable object
public class KNUserSketch implements Parcelable{
public int id;
public int user;
public String url;
public int views;
public int locations;
public KNUserSketch(JSONObject obj)
{
id = KNSafeJSonUtilties.safeGetInteger(obj, "id");
user = KNSafeJSonUtilties.safeGetInteger(obj, "user");
views = KNSafeJSonUtilties.safeGetInteger(obj, "views");
locations = KNSafeJSonUtilties.safeGetInteger(obj, "locations");
url = KNSafeJSonUtilties.safeGetString(obj, "url");
Log.v("JSON","jsonObject: "+obj.toString());
url.replace("https:", "http:");
}
public KNUserSketch(){
id=-1;
user=-1;
views = 0;
url ="";
}
public KNUserSketch(Parcel p){
id= p.readInt();
user = p.readInt();
url = p.readString();
views = p.readInt();
locations = p.readInt();
}
#Override
public int describeContents() {
// TODO Auto-generated method stub
return 0;
}
#Override
public void writeToParcel(Parcel dest, int flags) {
// TODO Auto-generated method stub
dest.writeInt(id);
dest.writeInt(user);
dest.writeString(url);
dest.writeInt(views);
dest.writeInt(locations);
}
public static final Parcelable.Creator<KNUserSketch> CREATOR = new Creator<KNUserSketch>() {
public KNUserSketch createFromParcel(Parcel source) {
return new KNUserSketch(source);
}
public KNUserSketch[] newArray(int size) {
return new KNUserSketch[size];
}
};
}

You could use SharedPreferences to put the objets in a safe place, but objets will have to implement Parcelable protocol.