Develop Reference

Switching between activities without losing custom data

Currently using an Intent with startActivity() to switch between 2 activities which share an abstract superclass. However, whenever startActivity() is called the custom object inherited from the abstract superclass gets reset. Is there anyway to maintain this object between startActivity() calls? Serializing the object with OnSavedInstanceState does not work because this object contains a LinkedList.

Every time a class is created regardless if it extends a superclass (in this case an Activity), the superclass is recreated. You would extend the Activity to share common methods/functions and imports....
You want to stay away from Serializable, so you want your object class to implement Parcelable:
public class CustomObject implements Parcelable {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
#Override
public int describeContents() {
return 0;
}
#Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(this.name);
}
public CustomObject() {
}
protected CustomObject(Parcel in) {
this.name = in.readString();
}
public static final Parcelable.Creator<CustomObject> CREATOR = new Parcelable.Creator<CustomObject>() {
#Override
public CustomObject createFromParcel(Parcel source) {
return new CustomObject(source);
}
#Override
public CustomObject[] newArray(int size) {
return new CustomObject[size];
}
};
}
In the first activity you want to pass the List to the second Activity using an Intent:
public class StartActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_start);
findViewById(R.id.btn1).setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(StartActivity.this, ReceiveDataActivity.class);
i.putParcelableArrayListExtra("KEY", getCustomObjectList());
startActivity(i);
}
});
}
private ArrayList<CustomObject> getCustomObjectList() {
ArrayList<CustomObject> itemList = new ArrayList<>();
for (int i = 0; i < 5; i++) {
CustomObject customObject = new CustomObject();
customObject.setName("Name " + i);
itemList.add(customObject);
}
return itemList;
}
}
Then to get the list you would use getIntent():
public class ReceiveDataActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_receive_data);
List<CustomObject> itemList = getIntent().getParcelableArrayListExtra("KEY");
Toast.makeText(this, "List size = " + itemList.size(), Toast.LENGTH_SHORT).show();
}
}

Passing an object from one android activity to another

I have a class that I'm using for parsing data from a csv file (called CSVReader), inside of that there is some methods for the parsing as well as a couple of strings and a list that is of a custom object type (List allRecords).
What I'm doing is when the app loads, parsing all the data into that list and then trying to pass that information along to the next activity but inside the next activity I keep getting allRecords as being null.
LoginActivity
CSVReader data = new CSVReader();
data.populateRecords(this);
Intent intent = new Intent(LoginActivity.this, Find.class);
Bundle bundle = new Bundle();
bundle.putParcelable("list", data);
intent.putExtra("bundle", bundle);
startActivity(intent);
I've gone through the debugger and the bundle definitely has the data in there.
Find
Intent intent = getIntent();
Bundle bundle = intent.getBundleExtra("bundle");
data = (CSVReader) bundle.getParcelable("list");
Using the debugger still, and mMap (in the bundle) is now null and so is data.
Am I doing something wrong? Both classes DummyData and CSVReader implement Parcelable.
EDIT: Adding custom class CSVReader:
List<DummyData> allRecords;
private String base;
private String location;
private String partner;
public static Creator<CSVReader> CREATOR = new Creator<CSVReader>(){
#Override
public CSVReader createFromParcel(Parcel source){
return new CSVReader(source);
}
#Override
public CSVReader[] newArray(int size) {
return new CSVReader[size];
}
};
private CSVReader(Parcel in){
allRecords = new ArrayList<DummyData>();
in.readTypedList(allRecords, DummyData.CREATOR);
base = in.readString();
location = in.readString();
partner = in.readString();
}
...
...
#Override
public int describeContents() {
return 0;
}
#Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(base);
dest.writeString(location);
dest.writeString(partner);
dest.writeList(allRecords);
}

[EDIT]
I was looking over your code again, and noticed you're writing the List to the parcel LAST and reading the list from the parcel FIRST. You have to read items from the parcel in the order they are written. Try putting dest.writeList(allRecords) at the top of the method so it is the first item written, or you can put in.readList(allRecords, DummyData.class.getClassLoader()) at the bottom of the list in that method.
Give it a shot.
//////////////////////////////////////////////
From the docs,
public final void readTypedList (List<T> list, Creator<T> c)
Read into the given List items containing a particular object type
that were written with writeTypedList(List) at the current
dataPosition(). The list must have previously been written via
writeTypedList(List) with the same object type.
You're using writeList() to write the data to the parcel. Try using writeTypedList(). You could also try changing readTypedList() with readList() I believe. Something like:
in.readList(allRecords, CSVReader.class.getClassLoader());
Hope this helps.

If you plan to pass data to another activity, you need to use objects of classes that implement Parcelable. Here is an example,
package com.weather.model;
import java.util.ArrayList;
import java.util.List;
import android.os.Parcel;
import android.os.Parcelable;
public class Forcast implements Parcelable {
private String id;
private String code;
private String message;
private City city;
private String count;
private List<Weather> weatherList = new ArrayList<Weather>();
public Forcast(){
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
public City getCity() {
return city;
}
public void setCity(City city) {
this.city = city;
}
public String getCount() {
return count;
}
public void setCount(String count) {
this.count = count;
}
public List<Weather> getWeatherList() {
return weatherList;
}
public void setWeatherList(List<Weather> weather) {
this.weatherList = weather;
}
#Override
public int describeContents() {
return 0;
}
#Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(id);
dest.writeString(code);
dest.writeString(message);
dest.writeParcelable(city, flags);
dest.writeString(count);
dest.writeList(weatherList);
}
public static final Parcelable.Creator<Forcast> CREATOR = new Parcelable.Creator<Forcast>() {
#Override
public Forcast createFromParcel(Parcel source) {
return new Forcast(source);
}
#Override
public Forcast[] newArray(int size) {
return new Forcast[size];
}
};
protected Forcast(Parcel in){
id = in.readString();
code = in.readString();
message = in.readString();
city = (City)in.readParcelable(City.class.getClassLoader());
count = in.readString();
in.readList(weatherList, Weather.class.getClassLoader());
}
}
I included City model so you can see how it goes for an object in comparison to list of objects. Assume you have a Forcast instance with all the values as 'forcast' ( Forcast forcast = new Forcast() or something similar)
Intent intent = new Intent(this, SomeActivity.class);
intent.putExtra(com.weather.model,forcast)
startActivity(intent)
I hope that helps

You need to put bundle object by using putExtras method. Then you can get the bundle by using getIntent().getExtras().
Intent intent = new Intent(LoginActivity.this, Find.class);
Bundle bundle = new Bundle();
bundle.putParcelable("list", data);
intent.putExtras( bundle);
startActivity(intent);
Intent intent = getIntent();
Bundle bundle = intent.getExtras();
data = (CSVReader) bundle.getParcelable("list");

Parcelable transfer fails

I'm trying my first Parcelable transfer and it doesn't go fine. This is my Parcelable class :
public class Element implements Parcelable, Serializable {
private static final long serialVersionUID = 1L;
String name;
String id;
byte[] password;
public static final Parcelable.Creator<Element> CREATOR = new Parcelable.Creator<Element>() {
public Element createFromParcel(Parcel source) {
return new Element(source);
}
public Element[] newArray(int size) {
return new Element[size];
}
};
private Element(Parcel in){
name = in.readString();
id = in.readString();
password = new byte[in.readInt()];
in.readByteArray(password);
}
public Element(String name,String id,byte[] password){
this.name=name;
this.id=id;
this.password=password;
}
#Override
public String toString() {
return name;
}
public int describeContents() {
return 0;
}
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(name);
dest.writeString(id);
dest.writeInt(password.length);
dest.writeByteArray(password);
}
}
As you see, it's a simple Parcelable with 2 String fields and 1 byteArray.
Now I send it to the second activity via my main one :
//Inside the main activity
Intent i = new Intent(MainActivity.this, DisplayActivity.class);
i.putExtra("element", (Parcelable)adapter.getItem(pos));
startActivity(i);
And then, I receive the Parcelable in the second activity :
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.display);
Element e = getIntent().getExtras().getParcelable("element");
//this line makes my app crash. No idea why.

Try it this way:
Element obj = new Element();
//set your data here before send
Intent i = new Intent(this, MyActivity.class);
i.putExtra("com.package.Element", obj);
startActivity(i);
Then to retrieve it:
public class MyActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bundle b = getIntent().getExtras();
Element obj = b.getParcelable("com.package.Element");
}
}

I was also struggling with the same issue. In your manifest in the MyActivity activity add:
android:launchMode="singleTop"
It solved the issue for me.
<activity android:name="com.example.myapp.MyActivity"
android:label="#string/title_myactivity"
android:launchMode="singleTop">
</activity>

Why would you implement both Parcelable and Serializable?

Android: passing object between activities and make it parcelable

New to Android programming. Having trouble to pass the object between activities and make it parcelable. Could somebody tell me what the problem could be? I want to know whether the logic is sound.
public class MainActivity extends Activity {
private Bundle MyActivityParams;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent intent = new Intent(this, MyActivity.class);
MyActivityParams = fillInData(MyActivityParams);
intent.putExtras(MyActivityParams);
startActivity(intent, savedInstanceState);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
private Bundle fillInData(Bundle bundle){
bundle.putFloat("com.company.MyActivity.FL", 12);
bundle.putFloat("com.company.MyActivity.VH", 100);
bundle.putFloat("com.company.MyActivity.const", 1);
return bundle;
}
}
public class DisplayActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
displayData();
}
private void displayData(){
//ActivityData is from MyActivity
ActivityData data = new ActivityData(getIntent().getExtras());
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_display, menu);
return true;
}
}
public class MyActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
displayParams();
}
private void displayParams(){
ActivityData dataBundle = new ActivityData((getIntent()).getExtras());
transfer(dataBundle);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_algorithm, menu);
return true;
}
public void transfer(ActivityData incomingdata){
startActivity(incomingdata.getIntent());
}
protected static class ActivityData{
private Bundle data;
private TextView text;
private Intent intent;
public ActivityData(Bundle bundle){
/*data = bundle;
intent = new Intent(null, DisplayActivity.class);
text = new TextView(null);*/
}
public void display(String key){
this.text.setText(data.getString(key));
//not allowed: startActivity(intent);
//not allowed either: setContentView(text);
}
public Intent getIntent() {
return intent;
}
public void setIntent(Intent intent) {
this.intent = intent;
}
public TextView getText() {
return text;
}
public void setText(TextView text) {
this.text = text;
}
public Bundle getData() {
return data;
}
public void setData(Bundle data) {
this.data = data;
}
}
}

Let's have a Person class
public class Person {
private String name;
private String email;
private int age;
public Person(int age, String name, String email) {
this.age = age;
this.name = name;
this.email = email;
}
}
A parcelable one would look like this
public class ParcelablePerson implements Parcelable {
private final Person person;
private ParcelablePerson(Parcel parcel) {
this.person = new Person(parcel.readInt(), parcel.readString(), parcel.readString());
}
public ParcelablePerson(Person person) {
this.person = person;
}
public Person getPerson() {
return person;
}
#Override
public int describeContents() {
return 0;
}
// This is the method where you disassembly your object to pieces
#Override
public void writeToParcel(Parcel parcel, int flags) {
parcel.writeInt(person.getAge());
parcel.writeString(person.getName());
parcel.writeString(person.getEmail());
}
public static final Creator<ParcelablePerson> CREATOR = new Creator<ParcelablePerson>() {
// And here you create a new instance from a parcel using the first constructor
#Override
public ParcelablePerson createFromParcel(Parcel parcel) {
return new ParcelablePerson(parcel);
}
#Override
public ParcelablePerson[] newArray(int size) {
return new ParcelablePerson[size];
}
};
}
The crucial thing in the process is to have the same order of the variables in private ParcelablePerson(Parcel parcel) constructor and public void writeToParcel(Parcel parcel, int flags) method... You can see it on the age property which is an int.

try this one.
ParcelTest.java
import java.util.HashMap;
import android.os.Parcel;
import android.os.Parcelable;
public class ParcelTest implements Parcelable {
private HashMap map;
public ParcelTest() {
map = new HashMap();
}
public ParcelTest(Parcel in) {
map = new HashMap();
readFromParcel(in);
}
public static final Parcelable.Creator CREATOR = new Parcelable.Creator() {
public ParcelTest createFromParcel(Parcel in) {
return new ParcelTest(in);
}
public ParcelTest[] newArray(int size) {
return new ParcelTest[size];
}
};
#Override
public int describeContents() {
return 0;
}
#Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeInt(map.size());
for (String s: map.keySet()) {
dest.writeString(s);
dest.writeString(map.get(s));
}
}
public void readFromParcel(Parcel in) {
int count = in.readInt();
for (int i = 0; i < count; i++) {
map.put(in.readString(), in.readString());
}
}
public String get(String key) {
return map.get(key);
}
public void put(String key, String value) {
map.put(key, value);
}
}
ExampleSupplierActivity.java
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
public class ExampleSupplierActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ParcelTest p = new ParcelTest();
p.put("green", "go");
p.put("yellow", "wait");
p.put("red", "stop");
Bundle b = new Bundle();
b.putParcelable("com.example.trafficlight", p);
Intent i = new Intent(this, ExampleConsumerActivity.class);
i.putExtras(b);
startActivity(i);
}
}
ExampleConsumerActivity.java
import android.app.Activity;
import android.os.Bundle;
public class ExampleConsumerActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bundle b = getIntent().getExtras();
ParcelTest p = b.getParcelable("com.example.trafficlight");
String red = p.get("red");
// ...
}
}

try this out this code work for me. but i have implement serializable rather than parcelable.
Try to implement parcelable rather than serializable . and try it if its work. i havnt tried this but implementing parcelable.
To pass and object to another activity:
in activity A
make sure the class implements the serializable interface
create a new intent
create a new bundle
use the putSerializeable method to add the object to the bundle with a key
put the bundle in the intent by using the putExtras method
start the activity using the startActivity method
Specifically,
Intent intent = new Intent(ShoulderExerciseScreen.this, ExercisesScreen.class);
Bundle bundle = new Bundle();
bundle.putSerializable("exercise", new Exercise("BenchPress));
intent.putExtras(bundle);
startActivity(intent);
in activity B
declare and object of the type you want passed
use the getIntent method to get the intent
use the getSerializeableExtra to get the the value using the key
cast the returned value from getSerializeableExtra and the desired type
Specifically,
Exercise ex = (Exercise)getIntent().getSerializableExtra("exercise");
if(ex != null)
{
//do something
}

Passing ArrayLists in Android

I'm trying to pass array lists between activities in Android. The lists contains strings. I've read a lot about Parcelable. Would I need to create a Parcelable to pass a String array list? As of now I am using putStringArrayListExtra() and getSringArrayListExtra() to pass the lists through intents.
Here is some of my code.
Intent load = new Intent(getApplicationContext(), HelloTabWidget.class);
load.putStringArrayListExtra("albums", albums);
load.putStringArrayListExtra("songs", songs);
load.putStringArrayListExtra("artists", artists);
load.putStringArrayListExtra("fileName", fileName);
This is my onCreate method for the acticity which obtains the array list.
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.songlist);
Bundle extras = getIntent().getExtras();
isArtists = extras.getBoolean("artists");
isAlbums = extras.getBoolean("albums");
isSongs = extras.getBoolean("songs");
Intent get = getIntent();
songs = get.getStringArrayListExtra("songs");
artists = get.getStringArrayListExtra("artists");
albums = get.getStringArrayListExtra("albums");
fileName = get.getStringArrayListExtra("fileName");
if(isArtists == true)
updateArtistsList();
else if(isAlbums == true)
updateAlbumsList();
else if(isSongs == true)
updateSongList();
}
The class which retrieves the list is supposed to create a listView from the data in the lists. Whenever I run the code i get nullPointerExceptions when trying to make the lists. I know that my listView code works, so I have narrowed down the problem to the intents which pass the array lists.
Thanks in advance.
EDIT:
Here are the first few lines from the logcat.
12-28 03:03:42.313: E/AndroidRuntime(873): FATAL EXCEPTION: main
12-28 03:03:42.313: E/AndroidRuntime(873): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.adam.mediaplayer/com.adam.mediaplayer.HelloTabWidget}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.adam.mediaplayer/com.adam.mediaplayer.MakeListActivity}: java.lang.NullPointerException

It depends on the type of arraylist
putIntegerArrayListExtra(String name, ArrayList<Integer> value)
putParcelableArrayListExtra(String name, ArrayList<? extends Parcelable> value)
putStringArrayListExtra(String name, ArrayList<String> value)
putCharSequenceArrayListExtra(String name, ArrayList<CharSequence> value)
Then you can read from you next activity by replacing put with get with key string as argument,eg
myIntent.getStringArrayListExtra("arrayListName");

Here is how you can pass an ArrayList :
MyListClass.java - Custom class
public class MyListClass implements Parcelable{
private int test;
public MyListClass()
{}
public MyListClass(Parcel read){
test = read.readInt();
}
public int getTest() {
return test;
}
public void setTest(int test) {
this.test = test;
}
public static final Parcelable.Creator<MyListClass> CREATOR =
new Parcelable.Creator<MyListClass>() {
#Override
public MyListClass createFromParcel(Parcel source) {
return new MyListClass(source);
}
#Override
public MyListClass[] newArray(int size) {
return new MyListClass[size];
}
};
#Override
public int describeContents() {
return 0;
}
#Override
public void writeToParcel(Parcel arg0, int arg1) {
arg0.writeInt(test);
}
}
MyParcelable.java
public class MyParcelable implements Parcelable {
private List<MyListClass> arrList = new ArrayList<MyListClass>();
private int myInt = 0;
private String str = null;
public String getStr() {
return str;
}
public void setStr(String str) {
this.str = str;
}
public List<MyListClass> getArrList() {
return arrList;
}
public void setArrList(List<MyListClass> arrList) {
this.arrList = arrList;
}
public int getMyInt() {
return myInt;
}
public void setMyInt(int myInt) {
this.myInt = myInt;
}
MyParcelable() {
// initialization
arrList = new ArrayList<MyListClass>();
}
public MyParcelable(Parcel in) {
myInt = in.readInt();
str = in.readString();
in.readTypedList(arrList, MyListClass.CREATOR);
}
#Override
public int describeContents() {
return 0;
}
#Override
public void writeToParcel(Parcel outParcel, int flags) {
outParcel.writeInt(myInt);
outParcel.writeString(str);
outParcel.writeTypedList(arrList);
}
public static final Parcelable.Creator<MyParcelable> CREATOR = new Parcelable.Creator<MyParcelable>() {
#Override
public MyParcelable createFromParcel(Parcel in) {
return new MyParcelable(in);
}
#Override
public MyParcelable[] newArray(int size) {
return new MyParcelable[size];
}
};
}
MainAcitivty.java
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
arrList.add(new MyListClass());
arrList.get(0).setTest(200);
MyParcelable object = new MyParcelable();
object.setMyInt(100);
object.setArrList(arrList);
Intent intent = new Intent(MainActivity.this,ReceiverParcel.class);
intent.putExtra("parcel", object);
startActivity(intent);
}
ReceiverParcel.java
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bundle b = getIntent().getExtras();
MyParcelable object = b.getParcelable("parcel");
System.out.println(object.getArrList().get(0).getTest());
System.out.println(object.getMyInt());
}