Develop Reference

pass an event to all related views in android

Is there any way to change multiple TextView text sizes all at once? Also they may or may not be in single ViewGroup. I was hoping of doing by creating some kind of trigger/event that would act like pub/sub but got no ideas. Any Possibility?

You could just use a class which you register the TextViews with. Then have a method which goes through all the registered TextViews and sets the font size. Somethings like:
public class TextViewTextSizer {
private List<TextView> textViews;
public TextViewTextSizer() {
textViews = new ArrayList<>();
}
public void registerTextView(TextView textView) {
textViews.add(textView);
}
public void setTextSize(float size) {
for (TextView textView : textViews) {
textView.setTextSize(size);
}
}
}

The recyclerview crashes when I update it

Please don't mark it as duplicate, as the solutions provided yesterday did not work.
I have populated a recyclerview, and it is working fine, albeit it loads a bit slowly.
However, say when I add a new name and update the recyclerview it crashes with the NullPointerException.
Below are the classes and code:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mainOnes);
recyclerView = (RecyclerView) findViewById(R.id.recycleOnes);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
recyclerView.setLayoutManager(linearLayoutManager);
recyclerView.setHasFixedSize(true);
adapter = new MusicRecyclerAdapter(list);
recyclerView.setAdapter(adapter);
populateList();
}
public void populateList(){
DisplayUsersList displayUsersList = new DisplayUsersList();
displayUsersList.execute();
}
public class DisplayUsersList extends AsyncTask<String, String, String> {
#Override
protected String doInBackground(String... params) {
...
}
#Override
protected void onPostExecute(String postData) {
try {
list.clear();
JSONArray jsonArray = new JSONArray(postData);
for(int i=0; i < jsonArray.length(); i++){
String forename = jsonArray.getJSONObject(i).getString("forename");
String surname = jsonArray.getJSONObject(i).getString("surname");
UserDetails userDetails = new UserDetails(forename, musicName, surname);
list.add(userDetails);
}
adapter.notifyDataSetChanged();
} catch (JSONException e) {
e.printStackTrace();
}
}
}
public class AddUsers extends AsyncTask<String, String, String> {
#Override
protected String doInBackground(String... params) {
...
}
#Override
protected void onPostExecute(String postData) {
populateList();
}
}
I think it is crashing because of the populateList() method call because I have already initialised everything
My logcat:
java.lang.NullPointerException
at georgezs.userdas.UserDBGUI$DisplayUsersList.onPostExecute(UserDBGUI.java:218)
at android.os.AsyncTask.finish(AsyncTask.java:741)
at android.os.AsyncTask.access$600(AsyncTask.java:197)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:654)
at android.os.Handler.dispatchMessage(Handler.java:100)
Line 218 is adapter.notifyDataSetChanged();
I tried instantiating the recyclerview in onPostExecute but it keeps crashing. My code works in the sense that it actually loads the data and displays it in a recyclerview. It just doesn't redisplay or reload when I call the populateList() method again.
This bug has been bugging me in my sleep literally - so any help and solutions would mean a lot to me
EDIT: I THINK I KNOW EXACTLY WHERE THE ERROR IS - IT IS IN THE POSTEXECUTE METHOD IN ADDUSERS CLASS.
Thanks

Just check if the adapter is not null before calling notifyDataSetChanged():
if (adapter != null) {
adapter.notifyDataSetChanged();
}
This happens because the AsyncTask executes asynchronously and by the time it finishes, the adapter might not be available anymore.

One option you could try is, instead of using
adapter.notifyDataSetChanged();
replace with
recyclerView.getAdapter().notifyDataSetChanged();
This is assuming for whatever reason, you have got your adapter set to null, but not shown in the code clearly above, while your recyclerview is still fully intact.
p/s: I also didn't see you update your latest retrieved data and insert into the adapter. You might want to check that as well.

You're handling variables outside the scope of your main class in a Threaded class which can always be sketchy. Granted AsyncTask is supposed to synchronize operations for you, I'm always cautious
Try passing your list and adapter to your DisplayUsersList class e.g.
DisplayUsersList displayUsersList = new DisplayUsersList(list, adapter);
displayUsersList.execute();
And in your DisplayUsersList make sure the reference of these is explicit e.g.
public class DisplayUsersList extends AsyncTask<String, String, String> {
private final List<UserDetails> list;
private final Adapter adapter;
public DisplayUsersList(List<UserDetails> list, Adapter adapter) {
this.list = list;
this.adapter = adapter;
}
...
Also, try moving the populateList(); to OnStart rather than onCreate
As although the variables are assigned they may still be initialising.
Edit
Could you try moving the call to the top level class e.g.
public void dataSetChangedCallback() {
adapter.notifyDataSetChanged();
}
And in your DisplayUsersList change adapter.notifyDataSetChanged(); to
...
dataSetChangedCallback();
...

Attempt to call a method but I get a NullPointerException

I want to create a connection through socket but I'm having trouble with the graphic of my App:
This is my activity:
public class Messaggi2 extends ActionBarActivity{
LinearLayout mLayout;
ScrollView scroll;
EditText scriviMessaggi;
Button invia;
Socket connessione;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.messaggi2);
mLayout = (LinearLayout) findViewById(R.id.LinearScrollLayout);
scroll = (ScrollView) findViewById(R.id.scrollView2);
scriviMessaggi = (EditText) findViewById(R.id.Scrivi);
invia = (Button) findViewById(R.id.Invia);
LavoraDietro asd = new LavoraDietro(connessione);
asd.execute();
}
private TextView createNewTextView(String text) {
final LinearLayout.LayoutParams lparams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT); final TextView textView = new TextView(this);
textView.setLayoutParams(lparams);
textView.setText(text);
textView.setBackgroundResource(R.drawable.balloon_broadcast_incoming_pressed);
return textView;
}
private TextView createNewTextViewSent(String text) {
final LinearLayout.LayoutParams llparams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
llparams.gravity = Gravity.RIGHT;
final TextView textViewSent = new TextView(this);
textViewSent.setLayoutParams(llparams);
textViewSent.setText(text);
textViewSent.setBackgroundResource(R.drawable.balloon_outgoing_normal);
return textViewSent;
}
public void AggiungiTextALlayout(String messaggio){
mLayout.addView(createNewTextView(messaggio));
aggiornaScroll();
}
public void AggiungiTextInviatoALlayout(String messaggio){
mLayout.addView(createNewTextViewSent(messaggio));
aggiornaScroll();
}
public void aggiornaScroll(){
scroll.post(new Runnable() {
#Override
public void run() {
scroll.fullScroll(View.FOCUS_DOWN);
}
});
}
}
This is my AsynTask class:
public class LavoraDietro extends AsyncTask<Void, Void, Socket> {
Socket connessione;
boolean vediSeDeviPartire;
Messaggi2 mess = new Messaggi2();
public LavoraDietro(Socket connessione){
this.connessione = connessione;
}
#Override
protected Socket doInBackground(Void... params){
try {
InetAddress local = InetAddress.getByName("192.168.1.71");
connessione = new Socket(local , 7000);
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
return null;
}catch(Exception e){
e.printStackTrace();
}
return connessione;
}
#Override
protected void onPostExecute(Socket result) {
super.onPostExecute(result);
if(result != null){
vediSeDeviPartire = true;
mess.AggiungiTextALlayout("Sono connesso al server");
mess.AggiungiTextALlayout("I canali sono aperi..");
}
else{
mess.AggiungiTextALlayout("ERRORE CONNESSIONE AL SERVER ");
}
}
}
Using this code when I start my app the connection is established and then it crashes. What I see on my Logcat is this Exception:
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
So I tried to delete the content of my onPostExecute and everything works perfect. So the mistake is to try to call the method AggiungiTextAlLayout on my AsyncTask class.
Can someone help me with this? Can someone suggest me something? I'm new in this field so I know that this is a stupid thing but I need help.
Thanks guys in advance
EDITED WITH THE SOLUTION
Thanks to Ataulm I got the problem and I solved it I changed the costructor of my LavoraDietro class (unfortunatly I can't change the name of variables and classes in English. But next time I ll use english Name of course )
LavoraDietro Class
public class LavoraDietro extends AsyncTask<Void, Void, Socket> {
Socket connessione;
boolean vediSeDeviPartire;
Messaggi2 action;
public LavoraDietro(Socket connessione, Messaggi2 action){
this.connessione = connessione;
this.action = action;
}
#Override
protected Socket doInBackground(Void... params){
try {
InetAddress local = InetAddress.getByName("192.168.1.71");
connessione = new Socket(local , 7000);
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
return null;
}catch(Exception e){
e.printStackTrace();
}
return connessione;
}
#Override
protected void onPostExecute(Socket result) {
super.onPostExecute(result);
if(result != null){
vediSeDeviPartire = true;
action.AggiungiTextALlayout("Sono connesso al server");
action.AggiungiTextALlayout("I canali sono aperi..");
}
else{
action.AggiungiTextALlayout("ERRORE CONNESSIONE AL SERVER ");
}
}
}
And in the Messaggi2 class I changed the call of the constructor in this:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.messaggi2);
mLayout = (LinearLayout) findViewById(R.id.LinearScrollLayout);
scroll = (ScrollView) findViewById(R.id.scrollView2);
scriviMessaggi = (EditText) findViewById(R.id.Scrivi);
invia = (Button) findViewById(R.id.Invia);
LavoraDietro asd = new LavoraDietro(connessione, this);
asd.execute();

Your AsyncTask has a reference to mess which is an object of type Messaggi2.
Messaggi2 is a subclass of Activity. You attempt, inside your AsyncTask, to create a new instance of that class.
The Android system has no awareness of this object; it has called none of the life cycle methods, such as onCreate() where the activity's layout would typically be inflated. This means that none of your views are inflated nor even initialised.
When you call mess.AggiungiTextALlayout("Sono connesso al server");, mLayout is null.
The NPE you see may likely not even be this one.
TL;DR: don't instantiate your Activity objects like Java objects; use them as specified within the Android framework.
I suspect you have this Activity starting correctly somewhere. The mistake is that you've not associated that activity with your Asynctask. When you create LavoraDietro, you pass a reference to the Socket in the constructor; you can also pass a reference to your activity, and assign that to the mess field, instead of calling new Messaggi2(). I'm not advocating this structure. But that is the issue at hand.
A few general tips to help you avoid this in future / or spot it faster:
be consistent with your naming; it's difficult to read your code when you're switching between English and Italian.
it's equally difficult for others to read your code if you don't maintain follow Java conventions with class/method names.
When you're extending Activity, it's typical to append the word "Activity" after your class; in this example new Messaggi2Activity() would have been easier to spot.
Where you're able, pass a Class's dependencies as parameters in the constructor; don't rely on constructing these dependencies yourself inside that class. Once you do this, you can begin to draw lines around what your class is responsible for; the less it's responsible for, the harder it is for your class to mess up.

That problem is for put a variable with no "data", verify your variables

Alter canvas with a button click in the main activity

I am struggling with the logic behind this, so any tips would be appreciated. I have two classes, one in which the fragment is created and one in which my custom view is created, and I am trying to do some animation. In the main layout, I have an edit text field and a button. What I want to do is to add to the custom view when a button is clicked, the text within the edit text will be added to the custom view. Thinking about HOW to do this, I am drawing a blank, and I am beginning to think it is not possible. Should I just create the edit text within the custom view? Here is the code showing what I am doing (but stuck on a next step, or whether or not I should scrap this approach and try a different one)
The main fragment
public class DestroyerView extends Fragment
{
private Context mContext;
Paint paint = new Paint();
private AnimatedNegative PositiveAnimatedNegative;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
mContext = this.getActivity();
View view = inflater.inflate(R.layout.activity_destroyer, container, false);
final Button fire = (Button) view.findViewById(R.id.destroy);
PositiveAnimatedNegative = (AnimatedNegative) view.findViewById(R.id.anim_view);
fire.setOnClickListener(new OnClickListener()
{
#Override
public void onClick(View arg0)
{
// logic here?
}
});
return view;
}
}
public AnimatedNegative(Context context, AttributeSet attrs)
{
super(context, attrs);
mContext = this.getContext();
h = new Handler();
mCalendarDbHelper=new CalendarDbAdapter(mContext);
mCalendarDbHelper.open();
}
private Runnable r= new Runnable()
{
#Override
public void run()
{
invalidate();
}
};
protected void onDraw (Canvas canvas)
{
String word = "This is a sentence";
paint.setColor(Color.parseColor("#1E90FF"));
paint.setStyle(Style.FILL);
canvas.drawPaint(paint);
paint.setColor(Color.BLACK);
paint.setTextSize(20);
x = this.getWidth()/2;
y = this.getHeight()/2;
canvas.drawText(word, x, y, paint);
}
}
... Now this would be much easier if I could reference the button inside of the custom view, but it doesn't seem I can do that, or if I could simply add to the custom view inside of the main activity class, but it doesn't seem that I can do that either (not without creating a new canvas, which seems to be doing too much for what it is that I want to do (just add the words)). So, finally, is the way I am currently trying to do this a dead end? Any help would be appreciated.

I think I got it. I'll call invalidate with the the AnimatedNegative object defined in my main activity, and then pass in the word from the edit text and a true value, so that I can check for it in the view and redraw. Added code shown below:
Within the main activity:
public void onClick(View arg0)
{
PositiveAnimatedNegative.invalidate();
PositiveAnimatedNegative.add = true;
PositiveAnimatedNegative.positive_word = "This is a positive word";
}
And within the custom view:
if (add == true)
{
canvas.drawText(positive_word, x,y, paint);
}

Accessing the members of a simple class in Android

I have a simple Java class which extends View in another package, and I am making a custom view using this class. I want to use it as a View in XML from another class, which is an Activity.
My custom View needs some data from that class, so I created an object of Pt class, which extends Activity. The object is created, but when I am use that object for accessing the members of the class that extends Activity, it does not show any members. Am I doing something wrong, or there is a better way to do it?
Here is my code. I have shown what I am expecting within the comments.
public class PlotView extends View {//class to make a custom view
Plot_View obj_plot = new Plot_View();
obj_plot.// here i am expecting it to show the members of that Plot_View class which is extending Activity
class Pt{
float x, y;
Pt(float _x, float _y){
x = _x;
y = _y;
}
}
Pt[] myPath = { new Pt(100, 100), new Pt(200, 200), new Pt(200, 500),
new Pt(400, 500), new Pt(400, 200) };
public PlotView(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
}
public PlotView(Context context) {
super(context);
// TODO Auto-generated constructor stub
}
#Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
Paint paint = new Paint();
paint.setColor(Color.BLUE);
paint.setStrokeWidth(3);
paint.setStyle(Paint.Style.STROKE);
Path path = new Path();
path.moveTo(myPath[0].x, myPath[0].y);
for (int i = 1; i < myPath.length; i++){
path.lineTo(myPath[i].x, myPath[i].y);
}
canvas.drawPath(path, paint);
}
}//
and here is my Plot_View Activity .i want to access these Arraylists defined here in this activity
public class Plot_View extends Activity implements OnClickListener {
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.plotview);
calculationForPlot();
findViewById(R.id.btn_measure).setOnClickListener(this);
initMirrorMatrix();
drawMatrix();
}
private void calculationForPlot(){
ArrayList<String> al_edit_A_ft = new ArrayList<String>();
ArrayList<String> al_edit_A_inch=new ArrayList<String>();
ArrayList<String>al_edit_B_ft=new ArrayList<String>();
ArrayList<String>al_edit_B_inch= new ArrayList<String>();
float x=0;
AndroidOpenDbHelper androidOpenDbHelperObj = new AndroidOpenDbHelper(this);
SQLiteDatabase sqliteDatabase = androidOpenDbHelperObj.getReadableDatabase();
String q="SELECT * FROM ab_measurement WHERE job_id=" +"\""+Settings.jobid +"\"";
Cursor cursor = sqliteDatabase.rawQuery(q,null);
if (cursor.moveToNext()) {
System.out.println(cursor.getCount());
m=Integer.parseInt(cursor.getString(4));
do {
try{
float a = 0,b = 0;
a=(float) Double.parseDouble(cursor.getString(6));
String number =String.valueOf(a);
System.out.println("aaa ggg"+number);
String int_part =number.substring(0,number.indexOf("."));
String float_part=number.substring(number.lastIndexOf(".")+1,number.length());
System.out.println("aaa values"+int_part);
System.out.println("aaa values"+float_part);
al_edit_A_ft.add(int_part);
al_edit_A_inch.add(float_part);
b= (float) Double.parseDouble(cursor.getString(7));
String number_b =String.valueOf(b);
System.out.println("aaa ggg"+number_b);
String int_part_b =number_b.substring(0,number_b.indexOf("."));
String float_part_b=number_b.substring(number_b.lastIndexOf(".")+1,number_b.length());
System.out.println("aaa values"+int_part_b);
System.out.println("aaa values"+float_part_b);
al_edit_B_ft.add(int_part_b);
al_edit_B_inch.add(float_part_b);
x= (float) Double.parseDouble(cursor.getString(3));
String ft_base =String.valueOf(x);
System.out.println("aaa ggg"+ft_base);
String int_part_ft =ft_base.substring(0,ft_base.indexOf("."));
String float_part_inch=ft_base.substring(ft_base.lastIndexOf(".")+1,ft_base.length());
System.out.println("aaa values"+int_part_ft);
System.out.println("aaa values"+float_part_inch);
}
catch (Exception e) {
}
} while (cursor.moveToNext());

Try this....
Create an object reference variable of Your_Activity type in the Java class, and initialize it in the contructor with the Context passed to it.
Activity class:
public class MyActivity extends Activity {
TextView myView ;
protected void onCreate(android.os.Bundle savedInstanceState) {
myView = (TextView)findViewById(R.id.myView);
Points myPoints = new Points(this);
myPoints.displayMsg("MY NAME IS VIVEK");
}
}
Java class:
private class Points {
public MyActivity mcontext;
////---------- a constructor with the Context of your activity
public Points(MyActivity context){
mcontext = context;
}
public void displayMsg( final String msg){
context.runOnUiThread(new Runnable() {
#Override
public void run() {
mcontext.myView.setText(msg);
}
});
}
}

From the way your commented line of code is incomplete, I assume you are using an auto-complete feature of your IDE.
My first suggestion is to change the name Plot_View to PlotActivity. This will help you avoid confusion when you return to this project in the future. Also, it will help avoid confusion when you ask questions here.
As for your actualy question, I assume you are referring to the following ArrayLists:
ArrayList<String> al_edit_A_ft = new ArrayList<String>();
ArrayList<String> al_edit_A_inch=new ArrayList<String>();
ArrayList<String>al_edit_B_ft=new ArrayList<String>();
ArrayList<String>al_edit_B_inch= new ArrayList<String>();
First you need to realize that these are not members of the Plot_View class. They are declared locally in the calculationForPlot() method. Although, it appears that you have not posted the entire Plot_View class, so you may have declared other ArrayLists elsewhere. If you are indeed referring to the ArrayLists that I pasted above, you will need to declare them as member variables in Plot_View rather than as local variables in calculationForPlot(). Then you can create getter methods to allow your View class to access them.