MAIN ACTIVITY
public class MyActivity() extends Activity
{
onCreate()
{
MyClass myobj=new MyClass();
}
public void Mymethod()
{}
}
//HELPER CLASS IN A SEPARATE FILE
public class MyClass()
{
MyClass(Context context)
{
}
}
I tried to call Mymethod() from an instance of MyClass.
I would really appreciate any help. Thanks.
Why not just pass the activity to the constructor like
public class MyActivity extends Activity {
onCreate(){
MyClass myobj=new MyClass(MyActivity.this);
}
public void myMethod(){
}
}
//HELPER CLASS IN A SEPARATE FILE
public class MyClass{
public MyClass(MyActivity act) {
act.myMethod();
}
}
Make that method as static so you can call without creating the class object
public static void Mymethod()
{}
and call like this way
MainActivity.Mymethod();
This is probably the best way to do it. This is how I'm doing it. It's called a Singleton Design Pattern:
public class MyActivity extends Activity {
private static MainActivity instance;
public static MainActivity getInstance() {
if(instance==null){
setInstance(this);
}
return instance;
}
public static void setInstance(MainActivity instance) {
MainActivity.instance = instance;
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setInstance(this);
}
}
If I'm understanding you correctly I believe you can solve your problems using an interface as a callback.
////ACTIVITY/////////////////////////////////
public class MyActivity() extends Activity {
onCreate()
{
MyClass myObj=new MyClass();
//Set the listener on the object. Created as anonymous
myObj.setListener(new MyClass.Listener() {
myMethod();
});
}
}
public void myMethod(){
}
//////Custom Class//////////////////
public class MyClass {
Listener mListener;
public interface Listener {
public void onInterestingEvent();
}
public void setListener(Listener listener) {
mListener = listener;
}
public void someUsefulThingTheClassDoes() {
//Do your code here and when you're ready to call the activity's method do this
mListener.onInterestingEvent();
}
}
I had an inner class that I wanted to pull out into a more general library "Helper" class. I had the same issue you do. I got around it by making the helper class abstract, with a single abstract method. Then in my project package I extended the helper class with a constructor call in the specific class.
public class MyActivity extends Activity {
onCreate() {
MyHelperClass = new MyHelperClass(this, "foobar");
}
public void myMethod() {
// Code...
}
}
// In a different file
public class MyHelperClass extends HelperClass {
private MyActivity mInstance;
public MyHelperClass(MyActivity act, String data) {
super();
this.mInstance = act;
this.mActivity = act; // Useful for calling generic Activity methods in the HelperClass
this.mData = data;
}
protected void callMyActivityMethod() {
mInstance.myMethod();
}
}
// In a different file
public abstract class HelperClass {
protected Activity mActivity;
protected String mData;
public HelperClass() {
// Subclass will set variables
}
protected abstract void callMyActivityMethod();
// More code for all the other stuff the class does
}
In this way, I have a helper class that contains the vast majority of the "work", and all I have to do is make a subclass with the constructor and one method in order to get access to the calling activity's method of interest.
You have to pass instance of MainActivity into another class, then you can call everything public (in MainActivity) from everywhere.
MainActivity.java
public class MainActivity extends AppCompatActivity {
// Instance of AnotherClass for future use
private AnotherClass anotherClass;
#Override
protected void onCreate(Bundle savedInstanceState) {
// Create new instance of AnotherClass and
// pass instance of MainActivity by "this"
anotherClass = new AnotherClass(this);
}
// Method you want to call from another class
public void myMethod(){
...
}
}
AnotherClass.java
public class AnotherClass {
// Main class instance
private MainActivity mainActivity;
// Constructor
public AnotherClass(MainActivity activity) {
// Save instance of main class for future use
mainActivity = activity;
// Call method in MainActivity
mainActivity.myMethod();
}
}
In MainActivity.class file
You have to pass MainActivity context from MainActivity Class. Then in MyClass you have to Get MainActivity context. Remember Context and MyActivity are two different reference.
public class MyActivity extends Activity
{
onCreate(){
MyClass myobj=new MyClass(MyActivity context);
}
public void Mymethod(){}
}
//HELPER CLASS IN A SEPARATE FILE
public class MyClass()
{
MyActivity context;
MyClass(MyActivity context)
{
this.context = context;
this.context.Mymethod();
//Or you can directly use activity context
context.Mymethod();
}
}
I decided to write the HelperClass MyClass as an inner class of MyActivity class. This allows it full access to parent class but the bad thing is now MyClass is restricted to MyActivity class only.
public class MyActivity() extends Activity
{
onCreate()
{
MyClass myobj=new MyClass();
}
public void myMethod()
{
}
}
//INNER CLASS
public class MyClass
{
public MyClass()
{
}
//I can directly access the MyMethod
myMethod();
}
Related
I have an activity which instantiate a class with an interface. How I can get the android context within MyClass with only the reference to the interface?
public class TestActivity extends Activity implements MyInterface {
#Override
public void onCreate(final Bundle savedInstanceState) {
final MyClass myClass = new MyClass(this);
}
#Override
public void onChange() {
}
}
public interface MyInterface {
void onChange();
}
public class MyClass {
public MyClass(MyInterface myInterface) {
// how to get context from myInterface ???
}
}
public class MyClass {
public MyClass(MyInterface myInterface) {
// Get Context
Context context = null;
if (myInterface instanceOf Context)
context = (Context)myInterface;
}
}
If your Activity (which extends Context) is implementing MyInterface and you pass that to MyClass, you just need to cast it to the appropriate type.
The context is only available in Activity classes or global Context, if you have to use the context, change your code:
public class TestActivity extends Activity implements MyInterface {
#Override
public void onCreate(final Bundle savedInstanceState) {
final MyClass myClass = new MyClass(this);
}
#Override
public void onChange() {
}
}
public interface MyInterface {
void onChange();
}
public class MyClass {
public MyClass(TestActivity activity) {
//now, you can use the context of your activity or do a cast
// to your interface
MyInterface interface = (MyInterface) activity;
}
}
I think you approached it a bit wrong, but I might miss understood your design concept what you want to achieve.
Create your Interface in the Class where you want to obtain the Context from and the use implement like you did in your activity.
YourContextClass() {
private MyInterface interface;
onCreate() {
interface.onChange(this);
}
public interface MyInterface() {
void onChange(Context context);
}
}
Then in your Activity class implement MyInterface, and inside the method, you can obtain the Context.
YourActivity implements MyInterface {
private Context context;
...
void onChange(Context context) {
this.context = context;
}
}
But this is only necessary if you really need the context from Interface... otherwise, in you Activity, I see you are extendingActivity, which gives you access to the Context with getContext();
I know I can use getApplicationContext() to get Context from sub class of ListActivity.
but PublicPar is common class, how can I get Context from this class.
public class SMSMain extends ListActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
Context my=getApplicationContext();
}
}
public class PublicPar {
public static void SetNotification(){
}
}
If you have a common (helper-type) class like your PublicPar class, the best you can do is to pass context as a parameter to each method:
public static void SetNotification(Context context) {
}
Remember to not set this context to any PublicPar class variable to avoid leaking it.
Try this. It should work:
public class SMSMain extends ListActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
// Context my=getApplicationContext();
new PublicPar().SetNotification(SMSMain.this)
}
}
public class PublicPar {
public static void SetNotification(final Context context ){
// You can proceed with using the context here.
}
}
If you don't want to pass the Context around as part of constructor argument, you can expose a static method in the application.
public class MyApplication extends Application {
private static MyApplication myinstance;
public MyApplication() {
myinstance = this;
}
public static Context getAppContext() {
myinstance.getApplicationContext();
}
}
I have an Activity and non Activity class. How to call a method in Activity class from non Activity class
public class MainActivity extends Activity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main2);
DataClass dc = new DataClass();
dc.show();
}
public void call(ArrayList<String> arr) {
// Some code...
}
}
public class DataClass {
public void show(ArrayList<String> array) {
// Here I want to send this ArrayList values into the call
// method in activity class.
MainActivity act = new MainActivity();
act.call(array);
}
}
Just create a callback interface inside the DateClass.
public DateClass {
public interface IDateCallback {
void call(ArrayList<String> arr);
}
private IDateCallback callerActivity;
public DateClass(Activity activity) {
callerActivity = (IDateCallback)activity;
}
...
}
public void show(ArrayList<String> array) {
callerActivity.Call(array);
...
}
//And implements it inside your activity.
public class MainActivity extends Activity
implements IDateCallback {
public void call(ArrayList<String> arr) {
}
}
Well there are several things you could do. I think the easiest for you would be to send the Context into DataClass like so:
DataClass dc =new DataClass();
dc.show(this);
And in your DataClass save the context into a global var Context context. Then use it like so:
((MainActivity)context).call(array);
((MainActivity)getContext).array();
Just make a singleton like:
TeacherDashboardSingleton:
public class TeacherDashboardSingleton {
public Teacher_Dashboard aa;
private static final TeacherDashboardSingleton ourInstance = new TeacherDashboardSingleton();
public static TeacherDashboardSingleton getInstance() {
return ourInstance;
}
}
myActivity class:
onCreate(....){
....
TeacherDashboardSingleton.getInstance().aa = this;
....
}
this will create an object of same instance as in activity
now you can use it from anywhere
MyActivity implements a CustomListener defined in MyClass.java. I have a function defined in MyClass that should trigger the listener and do some action(finish() MyActivity) defined in the activity. Somehow, I am getting null reference to the listener. Where am I going wrong?
Please refer to the code below!
MyActivity.java
import com.project.MyClass.CustomListener;
public class MyActivity extends Activity implements CustomListener {
Context context;
CustomListener listener;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
context = this;
myClass = new MyClass(context);
myClass.setOnCustomListener(listener);
}
public void doThisWhenTriggered()
{
...
}
}
MyClass.java
public class MyClass{
private Contect ctx;
ArrayList<CustomListener> listeners = new ArrayList<CustomListener>();
public MyClass(Context context)
{
super();
this.ctx = context
}
public interface CustomListener
{
public void doThisWhenTriggered();
}
public void setOnCustomListener(CustomListenerListener listener)
{
this.listeners.add(listener);
}
public void generateTrigger()
{
CustomListener listener = listeners.get(0);
if(listener != null)
listener.doThisWhenTriggered();
else
Log.d("MyAPP", "Listener is NULL");
}
}
MyBroadcastReceiver.java
public void onReceive(Context context, Intent intent) {
...
callMyClass(Context context)
}
public void callMyClass(Context context)
{
MyClass myClass= new myClass(context);
myClass.generateTrigger(context);
}
EDIT
The problem was BECAUSE of accessing different instances of MyClass in BroadcastReceiver and Listeners list as correctly pointed out by #Binyamin Sharet
The solution is to declare the listener list as static and also public void generateTrigger() as static so that the receiver's callMyClass looks like :
public void callMyClass(Context context)
{
MyClass.generateTrigger(context);
}
You never instantiate listener (declared as CustomListener listener;) and therefore its always null, you just need to set the activity as the listener, as it implements the interface:
myClass.setOnCustomListener(this);
As seen in your code, you create a new instance of the class in the receiver, so the listener you set does not exist in the listeners list of new instance, since the list is not static.
Its because
MyClass myClass = new myClass(context);
in MyBroadcastReceiver.java. This will create a new instance.
So I think it will be better to use MyClass.java as Singleton.
public class MyClass {
private Contect ctx;
ArrayList<CustomListener> listeners = new ArrayList<CustomListener>();
private static final MyClass singletonMyClass = new MyClass();
private MyClass() {
}
public static CustomListner getInstance() {
return singletonMyClass;
}
public interface CustomListener {
public void doThisWhenTriggered();
}
public void setOnCustomListener(CustomListenerListener listener) {
this.listeners.add(listener);
}
public void generateTrigger() {
CustomListener listener = listeners.get(0);
if (listener != null)
listener.doThisWhenTriggered();
else
Log.d("MyAPP", "Listener is NULL");
}
}
from MyActivity.java you can call
MyClass myClass = MyClass.getInstance();
myClass.setOnCustomListener(listener);
and similarly in MyBroadcastReceiver.java
public void callMyClass(Context context)
{
MyClass myClass= MyClass.getInstance();
myClass.generateTrigger();
}
Hope this helps!!!.
I have an activity which creates an object instance of my class:
file MyActivity.java:
public class MyActivity extends Activity {
TextView myView = (TextView)findViewById(R.id.myView);
...
Points myPoints new Points();
...
}
--------------------------------------------------------------
file Points.java:
private class Points {
...
HOW TO USE myView HERE ???
...
}
--------------------------------------------------------------
How do I use the UI objects in my class (which does not extend an
Activity)? Should I pass some context to my Points class? How do I do, exactly?
see you post, i've edited it , to fix the problem
hope it helps :=)
here is the Edit :
file MyActivity.java:
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("Hello World !!!");
}
}
--------------------------------------------------------------
file Points.java:
private class Points {
protected MyActivity context;
//add a constructor with the Context of your activity
public Points(MyActivity _context){
context = _context;
}
public void displayMsg( final String msg){
context.runOnUiThread(new Runnable() {
#Override
public void run() {
context.myView.setText(msg);
}
});
}
}
Your Points can't be a private class without being an inner class. So your code doesn't even compile...
Pass the view as parameter to the constructor of your Points class:
public class MyActivity extends Activity {
TextView myView = (TextView)findViewById(R.id.myView);
Points myPoints new Points(myView);
private class Points {
public Points(TextView view) {
// todo
}
}
}
You should do everything and pass back the value to the activity to handle UI instead of doing any UI related stuff in the point stuff.
You can pass the main Activity's context (using Points(getApplicationContext());) to the class as a constructor parameter. You could also pass the specific UI elements you want to manipulate.
A better way to do it, however, may be to have Points not know about the Activity. Have your Activity call Points methods and take the necessary actions based on the method output.
You could just pass the view to your class.
Points myPoints = new Points(myView);
private class Points
{
private TextView mTextView;
Points(TextView textView)
{
this.mTextView = textView;
}
}
i was in same trouble..
i found the simple way..
make a static variable and function ...
call from other class..
TestActivity.java
public class TestActivity extends Activity {
static EditText edit_text1;
public void onCreate(Bundle savedInstanceState)
{
.....
edit_text1 = (EditText) findViewById(R.id.edit_text1);
.....
}
public static void setMSG(String str)
{
edit_text1.setText(str);
}
}
Test2.java
TestActivity.setMSG("this is text");
Could work using an interface
file MyActivity.java:
public class MyActivity extends Activity implements Points.MyListener {
TextView myView;
... onCreate(...){
myView = (TextView)findViewById(R.id.myView);
Points myPoints = new Points();
//pass in MyActivity's instance of the listener
myPoints.addListener(this);
}
#Override
public void updateTextView(String message){
myView.setMessage(message);
}
}
file Points.java:
public class Points {
public Points(){
}
public interface MyListener{
void updateTextView(String message);
}
MyListener myListener;
public void addListener(MyListener listener){
myListener = listener;
}
public void updatePoints(){
//do some operations in calculatePoints()
String points = calculatePoints();
//update views using MyActivity's implementation of updateTextView()
myListener.updateTextView(points);
}
}
Doing it this way, events can be fired / messages sent, for lack of better terms, from the external class to update the Activity UI. This might be overkill if all sb need is to call a method in the Points class that returns something