Android Idioms -- Part I

[Jeffrey Peacock]

There are 2 basic ways to assign an onClick() listener to a button, or other View's that accept clicks.  The 1st is the old programmatic way:

final Button button = (Button) findViewById(R.id.button_id);
button.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {
        // onClick implementation
    }
});

The other mechanism is to declare the listener method using the attribute:

    android:onClick=”methodName”

in the layout XML that contains the Button.  Then define the method in the Activity that uses the layout like this:

/**
 **  onClick listener for ??? button
 **
 **  @param view the view the that received the click
 */
public void methodName(final View view) {
    // onClick implementation
}

So, which do you prefer?  Recommend?  What is the compelling argument for either or both?

Thanks.

/J

[Wolf Paulus]

Usually I’m very much in favor of a declarative approach, especially if it serves the separation of concerns. E.g. we are building the static UI declaratively in XML and the behavior in (Java) code. Binding the two however, is the tricky part, where should that happen?

I guess, if you screw up what you call,  "the old way” (R.id.button_id doesn’t exist) that can be caught at compile time, while using the declarative approach (missing method implementation) problems will only get caught at runtime.

Moreover, and here comes the more important argument, the declarative approach doesn’t work with Fragments, which is very how you should build your Android apps these days. So long story short, the "old programmatic way” is the new way and should be the preferred way to bind event handlers. 

   

Cheers

Wolf

— 

https://wolfpaulus.com

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[Jeffrey Peacock]

Have you verified with Fragments?  I think I did this th other day and it was fine.

/J

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[Ray Tayek]

pardon the top post, i go for the programmatic way.

i need to start some treads that run on the edt (see attached).

thanks

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-- 
Honesty is a very expensive gift. So, don't expect it from cheap people - Warren Buffett
http://tayek.com/

[Wolf Paulus]

http://stackoverflow.com/questions/6091194/how-to-handle-button-clicks-using-the-xml-onclick-within-fragments

Cheers

Wolf

— 

https://wolfpaulus.com

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[Jeffrey Peacock]

Unfortunately, as a comment to the article states, there is a fly in the ointment.

A button in a fragment layout, using the android:onClick=”methodName” attribute, will look for the listener in the Activity to which the fragment is attached. To my way of thinking this only gets us to programmatic definitions in Fragments – let’s not throw out the baby with the bath water.  However, considering that the convention is to name layouts for Activity’s with an ‘activity_’ prefix, and layouts for fragments with a ‘fragment_’ prefix; and the intimate knowledge that Activity’s have about their attached Fragment’s, and the initimate knowledge Fragment’s have about the Activity’s to which they are attached, seems to already allow for liberal cooperation.  This makes me wonder if there isn’t already enough convention and structure in place to allow for an idiom, a set of rules,  which continues to allow onClick methods to be declared in the XML.

I don’t have an immediate answer right now.  I need to think on this a bit.

Ideas?

/J

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[Jeffrey Peacock]

Ray,

We need to talk about some of your code:

    final GuiAdapterABC adapterFor1=new GuiAdapterABC(tablet.model) {
        @Override
        public void setText(final int id,final String string) {
            new Timer().schedule(new TimerTask() {
                @Override
                public void run() {
                    activity.runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            ((CheckBox)gui.idToButton.get(id)).setText(string);
                        }
                    });
                }
            },0);
        }

You're creating a Timer to schedule a Task to be run without delya to run something on the UI thread.  Get rid of the overhead and just do:

                    activity.runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            ((CheckBox)gui.idToButton.get(id)).setText(string);
                        }
                    });

/J

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[Ray Tayek]

On 10/13/2015 1:06 PM, Jeffrey Peacock wrote:

Ray,

We need to talk about some of your code:

    final GuiAdapterABC adapterFor1=new GuiAdapterABC(tablet.model) {
        @Override
        public void setText(final int id,final String string) {
            new Timer().schedule(new TimerTask() {...
            },0);
        }

You're creating a Timer to schedule a Task to be run without delya to run something on the UI thread.  Get rid of the overhead and just do:

                    activity.runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            ((CheckBox)gui.idToButton.get(id)).setText(string);
                        }
                    });

/J

iirc, that gets some error saying that i can not invoke gui stuff on the thread that is calling set text.

thanks

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[Jeffrey Peacock]

I don't know how that can hapen unless the time/sapce continuum is completely out of wack.

The contract of activity.runOnUiThread() is to run the Runnable on the UI thread so the UI can be updated.

/J

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[Ray Tayek]

On 10/13/2015 2:15 PM, Jeffrey Peacock wrote:

I don't know how that can hapen unless the time/sapce continuum is completely out of wack.

The contract of activity.runOnUiThread() is to run the Runnable on the UI thread so the UI can be updated.

/J

if i don't do that, i crash (please see below).

thanks

    --------- beginning of crash
10-13 15:44:01.346    2376-2399/? E/AndroidRuntime﹕ FATAL EXCEPTION: client
    Process: com.tayek.tablet.android, PID: 2376
    java.lang.RuntimeException: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
            at com.tayek.tablet.io.UdpClient.run(UdpClient.java:44)
            at java.lang.Thread.run(Thread.java:818)
     Caused by: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
            at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:6357)
            at android.view.ViewRootImpl.invalidateChildInParent(ViewRootImpl.java:909)
            at android.view.ViewGroup.invalidateChild(ViewGroup.java:4690)
            at android.view.View.invalidateInternal(View.java:11801)
            at android.view.View.invalidate(View.java:11765)
            at android.view.View.invalidate(View.java:11749)
            at android.widget.TextView.checkForRelayout(TextView.java:6858)
            at android.widget.TextView.setText(TextView.java:4057)
            at android.widget.TextView.setText(TextView.java:3915)
            at android.widget.TextView.setText(TextView.java:3890)
            at com.tayek.tablet.android.Build$2.setText(Build.java:33)
            at com.tayek.tablet.io.GuiAdapterABC.update(GuiAdapterABC.java:17)
            at com.tayek.tablet.android.Build.update(Build.java:173)
            at java.util.Observable.notifyObservers(Observable.java:138)
            at com.tayek.tablet.model.ModelBase.setChangedAndNotify(ModelBase.java:20)
            at com.tayek.tablet.model.ModelBase.setState(ModelBase.java:25)
            at com.tayek.tablet.model.Model.setState(Model.java:15)
            at com.tayek.tablet.model.ModelBase.receivedBroadcast(ModelBase.java:30)
            at com.tayek.tablet.model.Tablet.receivedBroadcast(Tablet.java:45)
            at com.tayek.tablet.Mediator.receivedBroadcast(Mediator.java:83)
            at com.tayek.tablet.io.UdpClient.run(UdpClient.java:38)
            at java.lang.Thread.run(Thread.java:818)
1

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