Actually, I want to pass a Variable type and Id into a class to initialize the variable.
Like, Button myButton=new MyClass(Button, myButtonId);
Here Button is variable type, and myButtonId is a id from xml.
And the class (method) will return something like that (Button)findViewById(R.id.myButtonId);
For this I wrote
Button myButton=new MyClass(Button, myButtonId);
And Android Studio Suggest me
private class MyClass extends Button {
public MyClass(Object p, Button myButtonId) {
super();
}
}
There is an error at super(); line.
I have no idea to do more.
Any suggestion?
You need to put at least one (context) parameter in the super function
Please check the public constructors for the Button class here:
Button public constructors
UPDATE
You need to pass an context to your class which is extending Button, something like this:
MyClass myButton = new MyClass(getApplicationContext());
And then in your MyClass:
public class MyClass extends Button {
public MyClass(Context context) {
super(context);
}
}
Related
I have been looking for a long time for a simple way to pass data (string type) from class to activity.
I found some tutorials about passing data from activity to class but is it possible to do the opposite, passing data from class to activity ?
if you import the class in your activity (which is also a class by the way) you can easily access the classes attributes.
example: MyClass.java
package edu.user.yourappname;
public class MyClass {
public string infoToPass = "whatever";
}
MyActivity.java
package edu.user.yourappname;
import edu.user.yourappname.MyClass
public class MyActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my);
String myString = MyClass.infoToPass;
}
}
i have no IDE to type this in atm it might contain some errors :S but i hope you get the idea.
if you need more specific help you have to provide a code sample.
also, what do you want to achieve exactly? maybie there's a different approach.
cheers!
Create Interface and implement that in your activity. Pass the activity instance in your class and and call that instance with interface method whenever you like.
To be more clear, create an interface and use it as following:
public interface SomeInterface{
public void passValue(String value);
}
public SomeActivity extends Activity implements SomeInterface{
// place any code you want in your activity, onCreate, onResume, etc.
private void someMethod(){
// Wherever in your activity, initialize your class with your activity.
SomeClass someClass = new SomeClass(this);
someClass.someMethod();
}
public void passValue(String value){
// do whatever you want with your value
}
}
public class SomeClass{
private SomeInterface someInterfaceInstance;
public SomeClass(SomeInterface someInterfaceInstance){
this.someInterfaceInstance = someInterfaceInstance;
}
public void someMethod(){
// Some code...
someInterfaceInstance.passValue("Hello World!");
// Some more code...
}
}
Here is a easy way of doing it -
By defining static variables
In your class, make the String whose value you want to pass public static like this -
public static String pass;
And then in you activity, you can directly access it since it's a public variable like this -
String receive = className.pass;
I have two Classes. Class A is an Activity that has integer variables that need to be used in Class B (not an Activity). I have been able to use Bundles to transfer data of variables from one Activity to another Activity before. The problem is that this time, Class B is not an Activity and extends ImageView so that the draw() function can be used. Because of this, I am unable to use normal Activity functions, such as Bundle-Intents or SharedPreferences to transfer data in primitive variables from Class A to my Class B. I receive an error saying that "getIntent() is undefined for type".
So my question is, how can Class B use the variables in Class A if I am unable to bundle? Is there another way?
Someone said they did not understand my question so hopefully the below example will help demonstrate better.
public Class1 extends Activity {
//so Class1 has some primitive data, and is an Activity w/layout
int var1;
int var2;
Bitmap bitmap;
#Override
protected void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.view);
}
}
A different class needs to draw onto canvas, but also needs to use the
information in var1 and var2 to be able to draw properly. But how to obtain that information?
public Class2 extends ImageView {
/*I am unable to use normal Activity functions, so I
*cannot onCreate, for example. I also cannot bundle,
*getIntent(), or use getSharedPreferences(). So how do I get var1
*and var2 value? */
}
Update: I was able to get this to work using getters. I attempted this before, but it was not returning the correct values. If anyone else ever gets stuck with this similar issue, remember to setup your variables with "static". I'm still learning all the differences, but without static my getter was not working. Once I added static to my variables, everything worked out. So that's one observational tip (even without fully understanding the logic as to why). Thank you to all the responders for your tips.
You can do this in different way.
First of all you can use static variable to do this. Such that you can declare a variable in class A public static String variable; and from class B you can get the value of this variable like this way ClassA.variable.
Another way you can use by passing a context of class A to B and then use SharedPreference.
Or create a new class which extends android Application. From class A you can set different variable value in application class. Now you can retreive those values from Application class. Hope this can help you.
Some code Sample using static variable
public Class1 extends Activity {
public static int var1 =20;
public static int var2 = 30;
}
Now get the variable value from class two
public Class2 extends ImageView {
Class1.var1;
Class.var2;
}
Second way using getter.
public Class1 extends Activity{
int var1 =10;
int var2 =20;
public int getVar1() {
return var1;
}
public int getVar2() {
return var2;
}
}
Now you can get the variable value in Class2
public Class2 extends ImageView {
Class1 class1= new Class1();
class1.getVar1;
class1.getVar2;
}
Also you can use SharedPreference. Hope it can help you. Thanks.
Various options exist:
The Activity can pass the information to Class B:
class B {
public void tellMeInformat(int usefulNumber) {
// Do something
}
}
Or, you can pass the Activity to the ImageView:
class A {
initiation {
B mySpecialImageView = /* Set it upo */;
B.setParentActivity(this);
}
}
class B {
private myA = null;
public void setParentActiviy {
myA = A;
}
private void doSomething {
int usefulNumber = A.getUsefulNumbner();
// Do something
}
}
I have created a custom application class like this:
class A extends android.app.Application{
public String abc = "xyz";
}
And I have a simple java class
class B {
private appContext;
// This constructor is called from activity.
B(Context ctx){
this.appContext = ctx;
}
private void foo(){
// want to access Class A's abc String vairable Here...HOW TO DO THAT?????
}
}
How to access Class A's abc String vairable in foo method.
You can get the Application class with getApplicationContext from Context with the good casting
((A) this.ctx.getApplicationContext()).abc;
The Application class in Android is a singleton and therefore so is your derived class. Android will create just one instance of your class A when it starts your application. Just change
class A extends android.app.Application {
public String abc = "xyz";
}
to
class A extends android.app.Application {
public static String abc = "xyz";
}
and you can reference it from anywhere like this:
String foo = A.abc;
Instead of passing a Context, try passing an instance of the Application class instead.
Something like:
class B {
private Application app;
// This constructor is called from activity.
B(Application ctx){
this.app = ctx;
}
private void foo(){
app.abc; //Do what you want
}
}
And call B like:
B b = new B(getApplication());
Make sure that this is in onCreate() or later.
Looks like you are already passing the application context as a parameter and initializing it in the constructor. So all you have to now is to use the context variable to access abc of A like the following way: ((A) this.appContext).abc;
i'm new here so still very blur with some certain things here.
& i'm a bit confuse with following codes.
public class SmsActivity extends ListActivity {
private String[] mSmsReceiver;
public SmsActivity(){
mSmsReceiver = new SmsReceived();
setListAdapter(new ArrayAdapter<String>(this, R.layout.main,mSmsReceiver));
my understanding: (should be wrong)
line 1: Class SmsActivity under a superclass ListActivity
line 2: i introduce a string array term name:mSmReceiver
line 3: calling method SmsActivity()
line 4: inside SmsActivity method, mSmsReceiver(a string array) call method SmsReceived
line 5: ArrayAdapter(in string form, loaded with the info. of mSmsReceiver) loaded into setListAdapter
My question:
pls correct my understanding upon code above.
line 5, what is this refers to?
(i checked on internet & books, it always says context. but i'm totally no idea what is context exactly means, anyone can explain what is context refering here?)
full codes:
import...
....
public class SmsActivity extends ListActivity {
private String[] mSmsReceiver;
public SmsActivity(){
mSmsReceiver = new SmsReceived();
setListAdapter(new ArrayAdapter<String>(this, R.layout.main,mSmsReceiver));
ListView listView = getListView();
listView.setTextFilterEnabled(true);
//---method is call when listitem is clicked---
listView.setOnItemClickListener(new OnItemClickListener() {edit later});
}
private class SmsReceived extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent)
{..... }
}
}
Basically this is a definition of a class named SmsActivity.
You are right about line 1 and line 2. More precisely, mSmReceiver is a private number of class SmsActivity.
Line 3 should be the constructor which I am not sure because I'm not an android developer and I heard it use onCreate instead in Activity. But anyway it wouldn't be calling the method just definition of it. The constructor will be used to initialize the class.
And line 4 mSmsReceiver(a string array) call method SmsReceived. Not the case, it would be initialize mSmsReceiver with an object, which is an instance of class SmsReceived.
Line 5 this refers to the class SmsActivity. In classes this almost always refers to the class it's in. And this provide a context so you can use this.someMumber or this.someFunction.
The keyword "this" in Java is basically a reference to the Class that its in. For example:
public class MyClass {
MyClass myVar = this;
}
This will put an instance of the class MyClass in that variable. It gives you an instance of whatever class your in. If you call it in a method:
public void myMethod() {
MyClass m = this;
}
This will give you an instance of whatever class invoked myMethod. Weather its an instance of MyClass or an instance of a subclass of MyClass. Whatever instance used to invoke the method will be placed in the m variable.
So when you call "this" in an Activity it gives you an instance of that Activity.
I have a problem to test my non activity-class which need the context of a activity class.
The class Card extends ImageView and have a few methods:
public class Card extends ImageView {
public Card(Context context, int cardID) {
super(context);
this.cardID = cardID;
this.turnback = 0;
backImage = getResources().getDrawable(R.drawable.backimage);
setBackgroundDrawable(backImage);
}
}
I would like to test this class as a standalone class, is there an opportunity to create an Dummy Context?
The simple answer is no. The reason being that you are extending a view. The only way to test a view is to view it. To do that you need an activity. This is android fundamentals.