So I have a main class and another class that has a variable I need to pull out into the main class. I have tried some of the ways posted on the answered questions like this, but I'm still failing to get it right.
public class Example extends MapActivity
{
public void OnCreate(Bundle savedInstanceState){
final Button bttn = (Button)findViewById(R.id.button1);
bttn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Toast tulos = Toast.makeText(getBaseContext(),
"Area is: "
+MyItemizedOverlay.alue +""
/*I get the non static variable error here
which I get as it is not yet defined, it will be after the user
inputs values into the program*/
,Toast.LENGTH_LONG);
tulos.show();
}
});
public class MyItemizedOverlay extends ItemizedOverlay<OverlayItem> {
int alue;
//irreleveant stuff (I assume)
public void Calc(Geopoint gp, Mapview map){
//there's some stuff before the variable I want to get like other variables
//not relevant for my problem I hope
alue = (int)Math.round(*formula: derived from user input data*)
}
}
So how can I get a value out of my other class, as it doesn't seem to be able to get it now? Or is this maybe an indication of a bigger problem?
There are two way
1 - make alue static but that will show the error that satic variable can't be accesses in non static function Calc so either make function Calcalso static as well or go to point 2
2-try this new MyItemizedOverlay().alue with making alue public as below
public class Example extends MapActivity
{
public void OnCreate(Bundle savedInstanceState){
final Button bttn = (Button)findViewById(R.id.button1);
bttn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Toast tulos = Toast.makeText(getBaseContext(),
"Area is: "
+new MyItemizedOverlay().alue +"" /<--------------------
/*I get the non static variable error here
which I get as it is not yet defined, it will be after the user has input
values into the program*/
,Toast.LENGTH_LONG);
tulos.show();
}
});
public class MyItemizedOverlay extends ItemizedOverlay<OverlayItem> {
public int alue; /<--------------------
//irreleveant stuff (I assume)
public void Calc(Geopoint gp, Mapview map){
//there's some stuff before the variable I want to get like other variables
//not relevant for my problem I hope
alue = (int)Math.round(*formula: derived from user input data*)
}
There is no access modifier for int alue means it is default.
Make it public int alue to be accessible from other classes.
Have a Look At Controlling Access to Members of a Class
Related
If I want to design a button that all java can use it without need to write it in every java,
what should I do?
For Example:
I design a Button.OnClickListener function to search bluetooth devices.
but another java also need to use this Button.OnClickListener function,
I don't want to write same way on two java.
ledWrite.xml:
<Button android:id="#+id/btnScan" />
<ToggleButton android:id="#+id/tBtnWrite" />
bluetoothUtils.java
// Intent request codes
private static final int REQUEST_CONNECT_DEVICE = 1;
private Button button_scan;
button_scan = (Button)findViewById(R.id.button_scan);
button_scan.setOnClickListener(new OnClickListener(){
public void onClick(View v) {
scanbt();
}
});
private void scanbt(){
Intent serverIntent = new Intent(this, DeviceListActivity.class);
startActivityForResult(serverIntent, REQUEST_CONNECT_DEVICE);
}
then I design LedWrite.java:
private ToggleButton digitalOutBtn; //LED On/OFF
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.ledwrite);
digitalOutBtn = (ToggleButton)findViewById(R.id.tBtnWrite);
digitalOutBtn.setOnClickListener(new OnClickListener()
public void onClick(View v){
if(digitalOutBtn.isChecked()){ //sendMessage("D1"); }
else{sendMessage("D0";}
}
How can I use button_scan in LedWrite.java?
If you want to call a method defined is some other Activity on press of a button, then you can make that method as static.
Let's assume that you have a method named searchBluetooth() in MainActvity and you want to call it from SecondActivity.
Define searchBluetooth() in MainActvity like,
public static void searchBluetooth()
Call this method from SecondActivity like,
MainActivity.searchBluetooth()
If you don't want to use static because of memory consumption then try with inheritance.
Create a class CommonActivity which extends Activity class
class CommonActivity extends Activity
{
// here define your searchBluetooth method
public void searchBluetooth()
{
// your code here
}
}
If you want to make use of it in Second Activity then
class SecondActivity extends CommonActivity
{
// here you can access `searchBluetooth()` method
}
enclosure a BluetoothListener class?
public BluetoothListener implements OnClickListener {
#Override
public void onClick(View v) {
do something you want...
}
}
then invoke the class in two different class, eg,
button.setOnClickListener(new BluetoothListener());
I recently started learning android and this answer may have some error, if so, please let me know, Thanks.
I'm new to android and I am making an app as part of an assignment, and can't get this function to return a value - the app closes and I get an error message: "Unfortunately, APP has stopped".
I have two classes, one is the MainActivity and one is a class that I am wanting to use to do arithmetic, and they are:
import com.calc.Calculation;
public class MainActivity extends Activity {
private Calculation util;
calculate = (Button) findViewById(R.id.btnCalc);
private TextView tvMultiply;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tvMultiply = (TextView) findViewById(R.id.tvMult);
}
btnCalc.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
tvMiltiply.setText(String.valueOf(util.CalculateMult(4,6)));
}
});
}
and
package com.calc;
public class Calculation{
public int CalculateMult(int numOne, int numTwo)
{
return numOne * numTwo;
}
}
I've tried a few alternatives but to no avail. It's going to be something simple that I am not doing quite right.
Any help appreciated.
Thanks
You need to create instance to the class before acccessing the member.
private Calculation util = new Calculation()
Else make the method in the class as static and access without creating instance.
This would be done by defining the class as:
package com.calc;
public class Calculation{
public static int CalculateMult(int numOne, int numTwo)
{
return numOne * numTwo;
}
}
and calling the method as:
Calculation.CalculateMult(4,6)
You should move the line
calculate = (Button) findViewById(R.id.btnCalc);
to the onCreate() function after you have set the content view. You should also move the assignment of the onClickListener to your button to the onCreate() method.
Finally, you should initialize your Calculation object by using the new operator in onCreate(), i.e:
util = new Calculation();
I stuck at this issue many times and I passed the problem in different ways and I'm not sure that I made it in the right way.
I simplified the problem in a the following example. I know that I can pass only the data to the class but I do want to pass the editText cause I have this problem with more difficult UI controls.
mainactivity.java
public class mainactivity extends Activity {
public EditText clickEditText;
int count =0;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
newTxt();
}
public void newTxt() {
txt = new MyText(context);
txt.updateTextEdit("Main Activity");
}
}
myText.java
public class MyText
{
private Context _context;
// constructor
public MyText(Context context)
{
_context = context;
}
public void updateTextEdit(String str)
{
private EditText strEditText;
strEditText= (EditText)findViewById(_context.R.id.editTextClick); // ????
strEditText.setText(str + " and myTxt");
}
}
if you could explain me how to fix the updateTextEdit function. i passed the context of the main activity. How can I change the editText? Thank you very much!!!
If you really want to do this this way, you need to save a reference to Activity, not Context. Like this:
public class MyText
{
private Activity _activity;
// constructor
public MyText(Activity activity)
{
_activity= activity;
}
public void updateTextEdit(String str)
{
private EditText strEditText;
strEditText= (EditText)activity.findViewById(R.id.editTextClick);
strEditText.setText(str + " and myTxt");
}
}
and in newTxt() you will need to change:
txt = new MyText(context);
to:
txt = new MyText(this);
But wouldn't it be easier to just put this method inside your activity? Why do you want it in another class? If it really needs to be in another class, you could make that class an inner class of your activity and you would still have access to the activity's methods and member variables.
There's a similar question here
How to access Activity UI from my class?
You didn't say how you obtained the context, you should use this and get the mainactivity in the other class. not context.
then you can call runOnUIThread to perform UI updates.
I simply have not found a solution to share a real-time data between the activitys. My first activity receives real-time object (type double, a random numbers). And i want to pas this numbers to second activity. It all works, only the second Activity shows only one time the data. I have to refresh the activity by going back to first activity and only then the second activity show the latest data. I implemented a Singelton pattern:
public class FirstActivity extends Activity{
public double xAxis;
public double yAxis;
public static FirstView instance;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.device_view);
handler = new Handler() {
#Override
public void handleMessage(Message msg) {
int data1 = msg.arg1;
xAxis = (double) data1;
dataX.setText(String.valueOf(xAxis));
int data2 = msg.arg2;
yAxis = (double) data2;
dataY.setText(String.valueOf(yAxis));
}
};
secondview.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent nextScreen = new Intent(getApplicationContext(),
SecondActivity.class);
startActivity(nextScreen);
}
});
}
public static void initInstance(){
if(instance == null)
{
instance = new FirstActivity();
}
}
public static FirstActivity getInstance(){
return instance;
}
}
SecondView class
public class SecondActivity extends Activity{
private double valueX;
private double valueY;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.linegraph);
valueX = FirstActivity.getInstance().xAxis;
valueY = FirstActivity.getInstance().yAxis;
}
}
Application class
package com.bluetoothcomm;
import android.app.Application;
public class MyApplication extends Application {
#Override
public void onCreate(){
super.onCreate();
initSingeltons();
}
public void initSingeltons(){
FirstActivity.initInstance();
}
}
You may implement a background service capable of providing the real time data to Activity1 and also to Activity2. I am guessing that your problem ocurrs if you are passing data from Activity1 to Activity2 through an Intent with putExtras, on this way it will only do this at the moment you start Activity2.
I have found my problem and the solution is to use Application. Only this dose not solves my problem. The problem is that the static variable instance public static FirstView instance is bound to the class loader, the first class that initilize that. So when the static variable inside any class has been initilized by an Activity and when the second Activity is started the first Activity is destroyed, so this means the static variable is also uninitilized. Thats why the SecondActivity dose not gets the up to date data or real time data, it catches only static constant data.
I changed my code a littele bit with the combination of Singelton and Application, couse this way the static variable should never be uninitilized when SecondActivity is activated. But i still get the same results, the static variable instance is uninitilized when i swtich to Second Activity. I am doing somethink wrong, does any one sees it. I added my code.
#Max Rasguido, #Orabig
You should use the intent process. docs
How is your data supposed to change when activity2 is shown, if you say that it's received by activity1 ?
However, I would use a preference, or an attribute of your application class (which is a singleton itself), but you give too little informations to fully understand your needs...
my dear friends. Could you help me to figure out where do I have memory leak in my application.
There are two activities.
In first activity I'v got a rather big static ArrayList consists of bitmaps and another needed information. I made it static, because I need to take it from another activity, and It's loading takes to much time.
In another activity, I also have one static field, using as a key for getting data which present in an Intent from previous activity.
If I try to start one activity from another and go back several times, I get shutting down VM.
To be more clear, here is a snippet of my code:
public class MoviesGallery extends Activity
{
...
private static ArrayList<Movie> films = new ArrayList<Movie>();
...
public void contextButtonsClickHandler(View v)
{
switch(v.getId())
{
case R.id.play_button:
Log.d("Context Button", "Play button has clicked");
mContextButtonHasPressed = true;
Intent filmData = new Intent(MoviesGallery.this, MovieInfo.class);
filmData.putExtra(MovieInfo.mPOS,mPOSITION_OF_CLICKED_ITEM);
startActivityForResult(filmData, 1);
break;
...
}
And this is another activity:
public class FilmInfo extends Activity
{
public static String mPOS = "pos";
private int mNumOfFilm = -1;
private LinearLayout mWall;
...
protected void onCreate(Bundle savedInstanceState)
{
Bundle extra = getIntent().getExtras();
mNumOfFilm=extra.getInt(mPOS);
...
Drawable d = new BitmapDrawable(MoviesGallery.getMoviesArray().get(mNumOfFilm).getWall()));
mWall = (LinearLayout) findViewById(R.id.Wall);
mWall.setBackgroundDrawable(d);
...
setResult(0);
}
I would suggest that potentially memory-leak point is in FilmInfo class member:
private LinearLayout mWall;
Layout has reference to Activity, which each time changes.
So to avoid keeping reference to dead Activity just use in FilmInfo class
#Override
public boolean onContextItemSelected(MenuItem item)
{
//blah-blah
mWall=null;
}
Anyway recipe is simple - try to avoid keeping objects which might contain references to Activity/Context objects.