Develop Reference

I want a clarification about in Android

I am a .NET developer who is in the beginning stage in Android development. Please explain me the code below.
nine=(Button)findViewById(R.id.b9);
nine.setOnClickListener(this);

nine = (Button) findViewById(R.id.b9);
Look for the view called b9, cast it to button, and assign it to your variable.
nine.setOnClickListener(this);
Add your class as a listener of clicks on that button if we are implementing the OnClickListener interface otherwise we have to create new OnClickListener using like this.
nine.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
}
});
P.S: This is not the way to learn Android.

nine=(Button)findViewById(R.id.b9);
It search the element by id (R.id.b9) and cast it to button and assign that value to the variable nine.
nine.setOnClickListener(this);
variable nine is button type variable so set the OnClickListener on this to fire some event after clicking on it.
and this activity must implement OnClickListener
public class a extends Activity implements OnClickListener {
}

get the activity ovject within action listener

Is there a way to get a pointer of activity which containing object of action Listener?
code snippet:
public class ActivityAsContainer exteneds Activity{
public static ActivityAsContainer _brokeTheAbstractBarier;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
_brokeTheAbstractBarier = this;
setContentView(R.layout.SomeBigLie);
final Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
brokeTheAbstractBarier.dance;
}
}
}
Is there a better way to pass the activity over to the action listener, then use a static global that could break if the object is created twice, and could a view be created twice and still live?

Just use
ActivityAsContainer.this
e.g
button.setOnClickListener(new View.OnClickListener() {
ActivityAsContainer.this.dance;
}

It should not be static.
You can use this definition in OnCreate and then use myActivity in the listener.
final Activity myActivity=this;

Hope you will be able to solve after using this line
_brokeTheAbstractBarier = YoursMainActivity.this;
instead of
_brokeTheAbstractBarier = this;
or you can use
ActivityAsContainer.this
which is
button.setOnClickListener(new View.OnClickListener() {
ActivityAsContainer.this.dance;
}

Android - Button not firing

Need help trying to figure out why the button onCLick event isn't working. I set it in onCreate but it doesn't seem to be working:
public class MainActivity extends Activity implements OnClickListener {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//Setup Refresh button listener.
Button btn = (Button) findViewById(R.id.btnRefresh);
btn.setOnClickListener(btnRefreshClick);
}
private OnClickListener btnRefreshClick = new OnClickListener(){
#Override
public void onClick(View v){
Toast.makeText(getApplicationContext(), "Get Data from Server", Toast.LENGTH_LONG).show();
}
};
}
I even took out the Toast call and tried to write to LogCat but when I put a breakpoint on the Log.e statement, it never gets there.

Your code is valid and works.
You just should remove implements OnClickListener if you don't override the method onClick directly in your activity.
Add your .xml to your question because the problem looks to be here

Are you sure you're pressing the right button? Are you sure you're resource id/layout is correct?

You're specifying an OnClickListener inside your onCreate() method... this isn't right. If your activity is implementing OnClickListener, there should be a derived onClick() method.
Use:
btn.setOnClickListener(this);
instead and pop up the toast from the onClick() method separate from your onCreate().
Otherwise, you can try this instead:
btn.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v){
Toast.makeText(getApplicationContext(), "Get Data from Server", Toast.LENGTH_LONG).show();
}
});
Technically, yours should work though, so make sure you're clicking the right button and that you don't have onClick in your layout xml for the button.

What do I use as a parameter for the setOnClickListener() method?

I'm trying to make multiple OnClickListener methods for 5 buttons in my program, and I've been able to declare them, and I made a switch using the xml id of what was clicked, but I need a parameter for the setOnClickListener method when I call it, and all that will work is null. I have also tried passing in this, so the method has context.
Here's some of the code:
add.setOnClickListener(null);
sub.setOnClickListener(null);
mult.setOnClickListener(null);
div.setOnClickListener(null);
equal.setOnClickListener(null);

The parameter has to be an instance of some object that implements the OnClickListener interface. One way to do it is to use an anonymous inner class:
add.setOnClickListener(new OnClickListener{
public void onClick(View view){
//your event handler code here
}
});
another way is to make your class implement OnClickListener --do that by changing your declaration to look like:
public class MyActivity extends Activity implements OnClickListener{
then define an implementation for the onClick method:
public void onClick(View view){
if(view == add){
//handle add button click
}else if (view == sub){
//handle sub button click
}
//etc
}
then to install the listener you could do:
add.setOnClickListener(this);

You are supposed to pass View.OnClickListener to this function, which is a listener that will get called once the button is clicked.
To do that, you can either:
Declare this listener in the layout XML, with the button, as specified in Button 4 in this site.
Create an instance of View.OnClickListener and pass it to setOnClickListener method as in the example below (Taken from android site which is a great source):
// Create an anonymous implementation of OnClickListener
private OnClickListener mCorkyListener = new OnClickListener() {
public void onClick(View v) {
// do something when the button is clicked
}
};
protected void onCreate(Bundle savedValues) {
...
// Capture our button from layout
Button button = (Button)findViewById(R.id.corky);
// Register the onClick listener with the implementation above
button.setOnClickListener(mCorkyListener);
...
}
Since View.OnClickListener is an interface, your activity may implement it as well, and be itself the listener, in this case, you will pass the activity instance(this) to the setOnClickListener method, but this is just one option, and not that recommended IMHO.

Coming from a .NET background, I struggled with the same thing at first. It's just a different syntax than .NET as java doesn't support properties, or events like I was used to. Here's a simple example of how to do this using a class level click listener variable...
#Override
private void onCreate(Bundle bundle) {
myButton.setOnClickListener(this.genericButtonListener);
}
private OnClickListener genericButtonListener = new OnClickListener() {
#Override
public void onClick(View v) {
//v represents your button
}
};

You need a concrete class here. For example:
imageView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// your code here
}
});

If you look at documentation, you will notice it takes View.OnClickListener as parameter. If you need five separate listeners, which you are not going to use anywhere else, you can pass an anonymous class implementing onClick(View v), like this
add.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v){
//do required actions here
}
});

Android - Two onClick listeners and one button

I have a custom TextView which is clickable. It defines its own onClick handler in order to change its appearance based on clicks. However if I then define a second onClick handler in my activity in order to do something based on the button being clicked, only one of the onClick functions is called. onClick is a void function - is there any way to say I didn't process this click, please pass it on to other onClick handlers?
To be more clear here is the code:
Inside MyCheckButton which extends TextView I have:
setOnClickListener( mClickListener );
private OnClickListener mClickListener = new OnClickListener() {
public void onClick(View v) {
toggle();
}
};
However I include MyCheckButton into my Activity, and of course I need to do something when its clicked so I attach another OnClickListener to it:
MyCheckButton button= (MyCheckButtonButton) findViewById(R.id.cb);
button.setOnClickListener(new OnClickListener(){
#Override
public void onClick(View v) {
// do something in the app
}
});
By calling setOnClickListener twice it appears that I am replacing the original listener so toggle() which changes the appearance is never called. How can I do something in my activity when this button is clicked if it is already using the onClick handler to change its appearance? I thought I would simply see both OnClickListeners getting called.

This is a bit dirty, but the way I would do this if you need multiple listeners is to register one that knows about the other. The first one (the one that's actually registered) will then need to know when to delegate to the other listener based on the conditions of the event. Actually, in reality, there's no real need to have two OnClickListener classes. The second class can implement whatever interface you want. Additionally, there's no need to create a special interface for what you need.
public class MyClickListener implements OnClickListener{
private SomeCustomClass mSecondListener = new SomeCustomClass();
public void onClick(View v){
if (needToForward){
mSecondListener.handleClick(v);
}else{
//handle the click
}
}
}
Then, in your code for your activity, you would do this
MyClickListener lstn = new MyClickListener();
mCheckBox.setOnClickListener(lstn);
Is there a reason this wouldn't work for you?
Alternatively, if you wanted, the second class could also implement the OnClickListener interface.
Additionally, if you need true bubbling, you could define your own interface that supports adding multiple click listeners to an intermediate class that happens to implement the OnClickListener interface. From there, in that class's onClick() method, you would iterate through the registered listeners calling the appropriate method.

A cleaner approach would be to use the CompositeListener pattern.
Taken from:
how can I set up multiple listeners for one event?
You'd have to add this class in your project:
/**
* Aux class to collect multiple click listeners.
*/
class CompositeListener implements OnClickListener {
private List<OnClickListener> registeredListeners = new ArrayList<OnClickListener>();
public void registerListener (OnClickListener listener) {
registeredListeners.add(listener);
}
#Override
public void onClick(View v) {
for(OnClickListener listener:registeredListeners) {
listener.onClick(View v);
}
}
}
Then add this on your MyCheckButton
private CompositeListener clickListener = new CompositeListener();
public MyCheckButton()
{
super.setOnClickListener(clickListener); //multi event listener initialization
}
#Override
public void setOnClickListener(OnClickListener l) {
clickListener.registerListener(l);
}
Both your calls to setOnClickListener would go through this override, get added to the list and get called when the event is fired. Hope it helps.

Since it appears I can only have one onClickListener per View. What I think I have to do is define an interface:
public interface MyOnClickListener {
public void onMyClick(View v);
}
Implement it from my activity and override the onMyClick function to do whatever I want and in the MyCheckButton class I'll need to pass a MyOnClickListener in the constructor save it and call listener.onMyClick inside the onClick handler.
Let me know if theres a better way. I considered using the onTouch handler in either the activity or the MyCheckButton class, but later if I add onTouch or onClick to either one I will get a difficult to notice bug.
My idea doesn't work because I don't know how to get a reference to the activity from my constructor:
public class TVCheckButton extends TextView {
private MyOnClickListener mListener;
public TVCheckButton(Context context, AttributeSet attrs) {
super(context, attrs);
mListener = ???;
}
}

Since only one OnclickListener works on Android 2.1 [I don't know about later versions) make the view private and static and create a static function that can change it e.g.
public class ExampleActivity extends Activity{
private SomeOtherclass someOtherClass;
private static Button b_replay;
public void onCreate(Bundle savedInstanceState){
someOtherClass = new SomeOtherclass();
b_replay = (Button) findViewById(R.id.b_replay);
b_replay.setOnClickListener(someOtherClass);
}
public static void changeReplayText(String text){
b_replay.setText(text);
}
}

A nice generic approach is to use a list of listeners, such as ListenerList and WeakListenerList from the Beryl library.

For some reason I could not use the answers above so here is an alternative:
//I had all of this in one method where I had two buttons, and based on external factors one would be visible and other would not aka 'gone'. So, I had that checked out! Hope it helps someone!!
Button b = (Button) findViewById(R.id.b_reset);
Button breakk = (Button) findViewById(R.id.b_break);
if ((findViewById(R.id.b_reset)).getVisibility() == View.VISIBLE) {
b.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//some code and methods...
}
});
} else if ((findViewById(R.id.b_break)).getVisibility() == View.VISIBLE) {
breakk.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//some code and methods...
}
});
}

In the first class, define a virtual button:
private static Button myVirtualButton = new Button(context);
... and a public method to register it:
public static void registerMyVirtualButton(Button b) { myVirtualButton = b;}
In the OnClickListener do whatever action is desired, and in the end, softclick the virtual button:
if (myVirtualButton!=null) { myVirtualButton.callOnClick(); }
In the second class, define a button and its OnClickListener with whatever action is additionally desired.
Transmit the button to the first class via registerMyVirtualButton.
Upon clicking the object of the first class, both actions will be executed.

You can attach an OnClick listener to the button in the following way :
Button button= (Button) findViewById(R.id.button1);
button.setOnClickListener(new OnClickListener(){
#Override
public void onClick(View v) {
// do something
}
});
Similarily, your TextView should have it's on OnClick listener.