Using activity objects in Intents - java

(I'm unsure if I am doing this correctly.)
I am creating a simple timetable app which has a main timetable activity with five buttons to five different days. When a button is clicked I want to start an activity that uses a base activity that takes in two int arrays which are just the codes of lessons to pass to a data class. How do I use this base class to create multiple different activities using intents when a button is clicked?
Timetable Activity (Simplified)-intent code not working.
public class TimetableActivity extends Activity {
private Button monABut;
int[] monAlessons = {5,2,6,5,5};
int[] monAteachers = {0,2,7,1,0};
public DayAOneActivity mondayA = new DayAOneActivity(monAlessons,monAteachers);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_timetable);
monABut = (Button) findViewById(R.id.monAButton);
monABut.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(getApplicationContext(),mondayA);
startActivity(i);
}
});
}}
Day activity constructor
public class DayAOneActivity extends Activity {
int[] lessonCodes;
int[] teacherCodes;
public DayAOneActivity(int[] lessonCode, int[] teacherCode){
this.lessonCodes = lessonCode;
this.teacherCodes = teacherCode;
}

The correct way to start activity is to use it's class:
Intent i = new Intent(TimetableActivity.this, DayAOneActivity.class);
startActivity(i);
Activity object itself is created by Android framework automatically

Related

Taking data from one activity and storing it in another

I am trying to build a very simple App in Android Studio to practice using Intents to send data from one activity to another. On my Main Activity I have a "Total" TextView and a button. When I click the button, it takes me to a AddNumber Activity where I can type in an integer and press a button. This then takes me back to the Main Activity and adds that integer to the total, updating the TextView. I want to be able to do this multiple times while I've got the app open so the total keeps going up.
I have tried using a ViewModel to store the information so it doesn't get reset every time the Main Activity onCreate method is run. However, every time I do this, it works once (e.g. if I add a 7 in my AddNumber Activity, the Main Activity total goes to 7). However, when I try again, the ViewModel seems to get reset so doesn't remember the 7 that I put in initially, so if I put in an 8, the total on the MainActivity just gets set to 8, rather than 15. Am I making a mistake somewhere that is causing the ViewModel to reset? I understood that ViewModels were a way of storing data while the app is open, but I can't seem to make it work.
Thanks so much!
MainActivity.java code:
public class MainActivity extends AppCompatActivity {
TextView totalTextView;
MainActivityViewModel viewModel;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
totalTextView = (TextView) findViewById(R.id.totalTextView);
viewModel = new ViewModelProvider(this).get(MainActivityViewModel.class);
totalTextView.setText(Integer.toString(viewModel.total));
getSetIncomingIntent();
}
public void addNumber(View view){
Intent intent = new Intent(this, AddNumber.class);
startActivity(intent);
}
public void getSetIncomingIntent() {
Intent incomingIntent = getIntent();
if (incomingIntent.hasExtra("value")) {
viewModel.newValue = incomingIntent.getIntExtra("value",0);
viewModel.addNumber();
totalTextView.setText(Integer.toString(viewModel.total));
}
}
}
MainActivityViewModel.java code:
public class MainActivityViewModel extends ViewModel {
int total = 0;
int newValue;
public void addNumber() {
total = total + newValue;
}
}
AddNumber.java code:
public class AddNumber extends AppCompatActivity {
EditText numberEditText;
int value;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add_number);
numberEditText = (EditText) findViewById(R.id.numberEditText);
}
public void addNumber(View view){
value = Integer.parseInt(numberEditText.getText().toString());
Intent intent = new Intent(this, MainActivity.class);
intent.putExtra("value", value);
startActivity(intent);
}
}
When I click the button, it takes me to a AddNumber Activity where I can type in an integer and press a button. This then takes me back to the Main Activity and adds that integer to the total, updating the TextView.
This is not what is happening. First you create a new AddNumber activity.
public void addNumber(View view){
Intent intent = new Intent(this, AddNumber.class);
startActivity(intent); // This launches a new AddNumber Activity
}
And then here you are creating a new MainActivity instance.
public void addNumber(View view){
value = Integer.parseInt(numberEditText.getText().toString());
Intent intent = new Intent(this, MainActivity.class);
intent.putExtra("value", value);
startActivity(intent); // This launches a new MainActivity
}
So you're basically building a giant stack of MainActivity / AddNumber instances.
You need to start AddNumber with startActivityForResult and then handle that in MainActivity. Then you will be working with the original MainActivity and the original ViewModel and you will be able to update it.
Please refer to the documentation on starting an Activity for result.
Hope that helps!

Losing data when sending between two classes

My app doesn't display anything when passing data from one class to another. I located through with the debugger that my ArrayList doesn't get the right value from the class.
I'm sending data with the following function:
public class Adaugare extends AppCompatActivity {
private ListView myListView;
private NumeAdapter numeAdapter;
String inume;
int ivarsta;
Intent intent = new Intent();
private ArrayList persoanaArrayList = new ArrayList<>();
public ArrayList getPersoanaArrayList() {
return persoanaArrayList;
}
public int getPersoanaArrayListsize() {
return persoanaArrayList.size();
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_adaugare);
myListView = (ListView) findViewById(R.id.persoana_list);
Button btn_fin = (Button) findViewById(R.id.btn_fin);
btn_fin.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
EditText nume_edit_text = (EditText) findViewById(R.id.ins_nume);
EditText varsta_edit_text = (EditText) findViewById(R.id.ins_var);
ivarsta = Integer.parseInt(varsta_edit_text.getText().toString());
inume = nume_edit_text.getText().toString();
persoanaArrayList.add(new Persoana(inume, ivarsta));
}
});
}
}
And recieving it with:
public class Afisare extends AppCompatActivity {
ListView myListView;
NumeAdapter numeAdapter;
Adaugare ad = new Adaugare();
int cate;
int i;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_afisare);
myListView = (ListView) findViewById(R.id.persoana_list);
ArrayList<Persoana> persoanaArrayList = new ArrayList<Persoana>(ad.getPersoanaArrayList());
numeAdapter = new NumeAdapter(this, persoanaArrayList);
myListView.setAdapter(numeAdapter);
}
The class Persoana is:
public class Persoana {
private String nume;
private int varsta;
Persoana(String inume, int ivar) {
this.nume = inume;
this.varsta = ivar;
}
public String getNume() {
return nume;
}
public int getVarsta() {
return varsta;
}
public void setNume(String nume) {
this.nume = nume;
}
public void setVarsta(int varsta) {
this.varsta = varsta;
}
}
Persoana is the main class, everything is saved in it. ad is an object of Adaugare, Adaugare being the class from which I've taken the code for getPersoanaArrayList. At debugging some values appeared at ad, namely Adaugare #4556, and persoanaArrayList remains null.
I need the persoanaArrayList so that i can initialize my Adapter and listView. Everything else in the code seems fine from step by step testing with debugger.
Your problem is with the following line in the Afisare class:
Adaugare ad = new Adaugare();
You can't simply new one activity from another activity and expect to access a shared list between them. To share instance data between java objects you need a reference to the other object. Creating a new instance will create a new empty list. That's why you are "losing" data. A quick fix would be to make the list static so it can be accessed from any instance.
But since you're dealing with Android, the right way to share data between activities is by using intent extras. The first activity starts the second activity via an intent. The first activity places the desired data in the intent as extras. The second activity uses getIntent() and the various methods on Intent to access the extras.
One last tip, in Android, you never use the new operator with Activities. Activities are created by the system to service an intent. If you find yourself using the new operator, that's a sign that you're doing something wrong.

Pass int to another Activity

Before you flame me:
I know there are uncountable tutorials out there, and I know myself how to pass data to another ACtivity, just like that.
In my case that's diffrent tho. "Usually" data is passed to another activity through Intents, Bundles ecc and the other Activity is started.
Here's my case:
I have an Item with 4 parameters (Image, String,String, int)
In an AdapterClass I have a PopUpView which retakes those 4 parameters.
What I'd like to achieve is the following:
With the click of a button, the 4th parameter, the int should be sent to the Main activity and inserted in a textView inside the MainActivity, without (here's the main diffrence between this and the other questions)launching the Main Activity.
How can this be done?
TIA.
use BroadcastReceiver to send that 4th int to MainActivity
in PopupView do these:
Intent intent = new Intent("SOMEACTION");
intent.putExtra("4th_int", value);
activity.sendBroadcast(intent);'
//In MainActivity:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
IntentFilter filter = new IntentFilter("SOMEACTION");
this.registerReceiver(mReceiver , filter);
}
#Override
public void onDestroy() {
super.onDestroy();
this.unregisterReceiver(this.mReceiver );
}
private BroadcastReceiver mReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
if (intent.getAction() == "SOMEACTION") {
// retrieve the 4th int value and update something in MainActivity
}
}
};

How to pass onClick function to Intent

I want to modularize the usage of my class but I have problem in passing function. I want to be able to pass an OnClickListener from 1 activity to this CoachmarkActivity.
I tried 2 different method:
1. Passing an OnClickListener to Intent
2. Passing a class, FollowUpClass, implements Serializable, which has method onClick.
You can see the code below. It is not complete code, but you should be able to comprehend this.
public class CoachmarkActivity extends Activity {
public static final String RES_LAYOUT = "RES-LAYOUT";
public static final String LISTENER = "LISTENER";
public static final String FOLLOW_UP = "FOLLOW-UP";
#Override protected void onCreate(Bundle savedInstance) {
setContentView(getIntent.getIntExtra(RES_LAYOUT, R.layout.activity_default))
Button button1 = (Button) findViewById(R.id.button1);
Button button2 = (Button) findViewById(R.id.button2);
// 1ST ATTEMPT
// I want to modularize this
OnClickListener onClickPassedFromIntent = (OnClickListener) getIntent().getSerializableExtra(LISTENER);
button1.setOnClickListener(onClickPassedFromIntent);
// 2ND ATTEMPT
final FollowUpListener folllowup = (FollowUpListener) getIntent().getSerializableExtra(FOLLOW_UP);
button2.setOnClickListener(new OnClickListener() {
#Override void onClick() {
// !! Here is error, exception thrown
folllowup.onClick();
}
});
}
/**
* Public method to be used in other activity.
* Invocation wanna be:
* CoachmarkActivity.startThisActivity(getActivity(), R.layout.coachmark1, new OnClickListener() {
* #Override void onClick() {
* // Do something
* }
* });
*/
public static void startThisActivity(Context context, int resId, OnClickListener listener) {
Intent intent = new Intent(context, CoachmarkActivity.class);
intent.putExtra(RES_LAYOUT, resId);
// !! Line below is error, onClickListener is not serializable, no method can accomadate below
intent.putExtra(LISTENER, listener);
context.startActivity(intent);
}
/**
* Public method to be used in other activity.
* Invocation wanna be:
* CoachmarkActivity.startThisActivity(getActivity(), R.layout.coachmark1, new FollowUpListener() {
* #Override void onClick() {
* // Do something
* }
* });
*/
public static void startThisActivity(Context context, int resId, FollowUpListener folllowup) {
Intent intent = new Intent(context, CoachmarkActivity.class);
intent.putExtra(RES_LAYOUT, resId);
intent.putExtra(FOLLOW_UP, followup);
context.startActivity(intent);
}
}
The abstract class:
public abstract class FollowUpListener implements Serializable {
public abstract void onClick();
}
The problems are stated in the comment in source code above, with tag "!!" (Just CTRL+F "!!"). What I want to do is like passing a Delegate object (function in form of variable) in C#, but in Android Java.
Any idea? Thanks.
You are trying to add a Serializable extra to your Intent, but OnClickListener does not implement that interface. You can achieve what you want by creating a class that implements both of the interfaces you need.
private class SerializableClickListener implements View.OnClickListener, Serializable {
#Override public void onClick() {
// TODO handle click
}
}
However, just because you can doesn't mean you should. Sending a click listener to another activity is a horrible code smell, and you should really rethink how you could do this via Intents/Broadcasts.
I tried to pass the OnlclickListener and I couldn't. then I tried this solution.
I made a static click listener variable in a GlobalData class
public static View.OnClickListener btn;
Then when I call the startactivity to go to another activity I did this.
GlobalData.btn = new View.OnClickListener() {
#Override
public void onClick(View v) {
//Listern action
}
};
c.startActivity(new Intent(c, DialogActivity.class));
Then in the second activity, I can set the static listener reference which I used to assign a listener object in the first activity.
b1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(GlobalData.btn!=null){
GlobalData.btn1.onClick(v);
}
finish();
}
});
I didn't use it directly as a parameter so I can do other stuff in the second activity listener. this worked for me.
But you have to think more because you are using a static reference. this is not a 100% solution. but it's worth trying.

Best way to store list of activities to be called from another activity

I have following goal: From a list in main activity that extends ListActivity, I want to start other activities.
This is the code of the main activity:
public class SelectionWidgetsExampleActivity extends ListActivity {
private Class[] demos = {ListViewDemo.class, ChecklistDemo.class};
private ArrayAdapter<Class> aa;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
aa = new ArrayAdapter<Class>(this, android.R.layout.simple_list_item_1, demos);
setListAdapter(aa);
}
#Override
protected void onListItemClick(ListView l, View v, int position, long id) {
Intent intent = new Intent(this, demos[position]);
startActivity(intent);
}
}
My question is
How would you solve the issue of having list of classes to be executed outside the code of the main activity?
My first idea was to put it into xml resource file as string array. I can then easily create array of Strings from the resource, but don't know how to convert the string to the class - I need something like:
SomeJavaClass.getMeClassFromString(demos[position])
Do you need Class#forName(String className)?
It will solve your issue.
But what's wrong with your initial (posted) solution? I'd rather keep it than use dynamic class loading, only would changed modifiers of demos to private static final.

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