hello, Ron!

how can I help you today?

Hi Mark!

I am trying to display a web view from an Activity started from another activity. I want the user to be able to return to the original activity via the back button. The problem is that it takes two back button taps to achieve this. I can't seem to catch the first one on any callback.

Hi :)

I am not aware that a WebView automatically grabs the BACK button

(BTW, hello, Gabriele -- be with you shortly!)

no problem, just reading :P

I don't have any question :)

Ron: what OS level are you using, and what callbacks did you try?

I have onBackPressed and onPause, but these seem to catch the second one. It occurs on 2.3.6 and 4.2.

Is it something the webpage is setting?

does it make a difference what, if anything, the user has done in the WebView itself?

There isn't much to do in the webview but look at it.

Very reproduceable

so you get this even though the user has not clicked any links, etc.?

Correct. Just on entry.

I have not run into this personall

er, personally

for example, in the APK edition of my book, bringing up help does not require multiple BACK presses to return

The first back button generates a blank screen.

On mine.

I would use Hierarchy View and/or uiautomatorviewer to determine where you are at that point in time (blank screen)

(BTW, hello, EGHDK, be with you shortly!)

IOW, what activity are you on, what widgets are visible, etc.

for example, are you *sure* that what you are reading the Web content in is actually your app?

I can definitely see your scenario occurring if a server redirect caused the content that you thought was coming up in a WebView to go into the user's default browser

let me take questions from the others, and I can swing back to you in a bit

Gabriele: just double-checking -- do you have a question?

OK, EGHDK: do you have a question?

Okay, so I have a problem in my application. It's released for API level 15+ so it works fine on thsoe devices. I have a problem with 2.3 devices (API 10). For some reason every time I press the back button once I drilled deeper down into the application, I go back to the previous activity and the entire screen is white. And it stays there. If I click any button on that screen, the onCLick of that buttons fire appropriately. I don't know how to begin to debug. I have tried heirchy viewer

The button fires appropriately, and the screen comes back into view.

so, until the first touch event, the screen is white, and once you touch something, it draws?

Yeah it won't draw until I otuch something.

But I have to touch a button, hitting "white space" doesn't do anything.

not sure how you are getting into that state

try calling invalidate() on your top-level container, or the FrameLayout known as android.R.id.content, and see if that helps

It happens on every 2.x device.

call that in onResume(), or perhaps onStart()

onStart? I will try that. It doesn't only happen on the main drawer activity though

what I suggested was a hack, just to temporarily get you past the problem

Main drawer activity is activity A. I click a button to go to activity B, and I click another button to go to activity C. If I press back (to get to B) I will still get a white screen on B.

And B has nothing to do with the drawer at all.

well, I never implied anything about a drawer

I have never seen the behavior that you are describing, though, and so I don't have any particular recommendations on a more permanent fix

Anything else that I could try?

play around with some other project for a bit

such as any of my book samples

To debug? The only other information is that I have a bunch of libraries.

if you do see this behavior in the other samples, then there's something up with your device(s)

That I'm using. I have thought about slowly removing libraries to see if that will fix anything.

if you do not see this behavior in the other code, start adding in stuff of note until the behavior pops up

No, I've tried my own sample applications. And it works fine.

It's only in my one app, but I was always testing on a gnex, so I never noticed the problem.

right

ah

yeah, unfortunately, this tends to be a bit of "debugging by weedwhacker" at this point

I thought that maybe it was a listView issue so I tried cacheColorHint, but nothing came from that.

it feels like something is interfering with the normal redraw when you come back into the foreground

and I have no idea what would do that or how

other than it is probably something that you are using in all affected activities

let me swing back to the others, and I'll return to you in a bit

Ron: do you have another question?

Back on webviews. I may be off on terminology. Not a lot of experience with webview. I specify a webview layout and do a loadUrl into it.

and that's fine, so long as the URL does not result in a redirect request from the server

if the server sends back a 301 or 304 or something, the default behavior of a WebView is to load the redirected-to URL in the default browser

you can use WebViewClient and shouldOverrideUrlLoading() to control this behavior

OK, thanks. I'll look into it.

Sean: hi! do you have a question?

hi! yeah, i had a quick question on using SQLLite

in my application, i've been storing data in a flat file and also holding it all in memory to reduce how often i need to read from the disk

and recently i've been considering switching to SQLLite and maybe a content provider

OK... but what is your question?

i was reading your section about using SQLLite with listviews... so does it query the DB (and read from disk) every time it refreshes the listview?

that is one approach, and usually the default one

same thing happens with a ContentProvider and a CursorLoader

okay, if that's standard then i might go with that... i just wasn't sure, i thought reading from disk so often might be bad

well, the first rule of disk I/O is to do it on a background thread

which reduces the impact

yeah, i need to make that change... i just found out about StrictMode and i've been reading on the main thread

keeping a live copy of an in-memory cache up to date and synchronized properly with the database and all other users of the data gets complicated

i also have a map view... would it be easy to integrate with the DB as well?

well, that depends on what you mean by integrating a MapView with a database

each instance has its own coordinates so the mapview displays the same number that the listview does

you mean that you are using markers on the map, one per database entry?

yeah, sorry

that should not be especially hard, though the devil is in the details

in particular, things get messy if you need to display information in an info window that you do not already have in memory (e.g., as columns in the Cursor)

I'll have some stuff on that particular problem in the next book update

let me take questions from the others, and I'll be back with you in a bit

Jeff: hi! do you have a question?

okay

hi Mark

I'm drawing what should be a simple screen: header/title, list fragment, and edit text

when I use linear layout, then a large number of list entries pushes the edit text off the screen

use weights to control

give the ListView a height of 0 and a weight of 1

give the EditText a height of wrap_content (and the default weight of 0)

relative layout solves that problem using align bottom and below

that too can work

but the relative layout fills the screen with the edit text when the list is empty

oh, sorry, misunderstood how you were using the RelativeLayout

change the EditText to be alignParentBottom=true and no other RelativeLayout rules

change the ListView to be alignParentTop=true and above=@id/yourEditText

ahh - above

you want to have the EditText be its natural height, and stretch the ListView to fill available space

exactly

I see

thanks

I felt like I was taking the long way around the barn

Gabriele: if you come up with a question, chime in!

well, sometimes, it's a rather large barn :-)

EGHDK: do you have another question?

Not really. Unless my original question marinated in your head long enough for you to pose another plan of attack.

I will add in the invalidate onstart. I just wish I knew when this problem started happening.

not really, no, sorry

this is one advantage of a service like Apkudo

free monkey testing across a lot of devices

can you repeat the problem?

running that every so often would help catch these things before a manual test might

Yes I can repeat the problem.

btw, I use apkudo and like it - not perfect but helpful

Jeff: his problem was that on a BACK press, his activities were coming up visually blank until tapping on something

It happens every time in my app. I thought maybe it was Action bar sherlock. but nothing on SO points to that.

yeah, lots of my samples use ABS, and I have not had that problem on Android 2.x

Anyway. Okay, so other question is a programming one. Since I don't really understand some of the more general concepts in OOP/java.

do you override onStop() and onPause()?

@ Jeff. Yes I do.

bummer

Just weird that it works perfectly on 2.3

So Mark, "What is a callback?" I hear that a lot, and I feel like I know what it means. But your definitions have been helpful to clear things up as well.

in the context of Android, a "callback" is some method of yours being invoked by the framework

this will either be something you are overriding from a parent class, or a method on an interface that you are implementing

so, onCreate(), onClick(), onListItemClick(), would all be considered callbacks

Gotcha.

What about onPause onStop?

same thing

again, if *Android* is calling *you*, a common convenience term for that is a callback

it's not the most scientific term out there

but, it's a convenient shorthand

Gotcha. Cool. That's what my idea of a callback was, so that's good. lol

Sean: do you have another question?

just one followup: you said earlier that things get tricky if you want to display info that's not in memory... did you mean things not held in the Cursor?

or including columns in the Cursor

yes, and I mean *specifically* for an info window to be displayed when the user taps on a marker

okay... the info displayed in the info window would be within the Cursor, so i'll get to researching and implementing

thanks for your help

Jeff: do you have another question?

EGHDK: do you have another question?

OK, if anyone has a question, feel free to chime in

I guess I'm having a tough time learning what an interface is. I've read a ton about them, but I've never found a use for them in java or android (yet) but I hear them talked about a lot. Any examples you can throw at me? Or any github resources on it from you?

refresh my memory: what other programming languages do you know?

Erm... none really.

ah

OK

an interface is pretty much just what the name implies

it is a basket of method signatures, that implementers of that interface must implement

you use this for things like polymorphism

so, for example, to respond to a click on a widget, you need to call setOnClickListener() on the View

Yeah, so I kinda know what it means. I have seen youtube videos explaining it, but I guess in the context of Android, do you have any more examples with it?

you pass in an implementation of an OnClickListener interface

the View does not care *what* the actual underlying object is, from a class standpoint

all it knows and cares about is that the object implements the OnClickListener interface

and therefore we can call onClick() on it

you can think of the standard US 3-prong AC outlet as being an interface to the power in your home

But I've never done MainActivity extends Activity implements OnClickListener. And I have setOnClickListeners on thousands of views.

the outlet does not care whether you are plugging in a television, a toaster, or a teakettle, so long as it has those three prongs

*every* time you called setOnClickListener(), you passed in an implementation of the OnClickListener interface

whether you implement OnClickListener on the Activity, on the Fragment, or on something else is largely up to you

(garbage collection and OO design considerations aside for the moment)

Interesting. Okay, where would I find "proof" that I'm passing an implementation of the OnCLickListener interface when I set it on a view?

Is that interface implemented in the View object?

if you don't, your code will not compile

no, View does not implement OnClickListener

Hmm... okay. I still don't understand where I'm implementing it then.

I thought setOnCLickListener was just a mthod of a view.

it is

myButton.setOnClickListener(foo);

Foo is the interface?

foo must implement the OnClickListener interface for this code to compile, assuming that myButton is an implementation of the android.view.View class

here, foo is a parameter being passed to setOnClickListener()

you *really* need to step away from Android development for a while and read a book on Java

Gotcha. Okay, if you have any more examples where I would use "... extends Activity implements XYZ" in Android. Let me know. I see a couple of people online that voice strong opinions about interfaces, and I'm just sitting here like... I've never implemented an interface.

Yeah, I guess I might purchase that head first java book.

what you are probably seeing in terms of "strong opinions" is *where* you implement the interface

You think head first java will cover java timers and threads etc?

I would hope it would cover threads

Timer is largely deprecated, and usually not the right choice in Android anyway

Hrm... I was thinking about doing a project with Timers. What would be the right choice in Android?

SInce timers were in java, I thought I'd go with them.

well, it depends on what you are trying to do

Yeah, I guess it can go a few ways. But if I was just trying to keep count of something, I thought java timers sounded good enough

usually, to count, an integer is enough

and that's a wrap for today's chat

Yeah. Alright, looks like we're closing up.

Thanks Mark

the chat transcript will be posted to http://commonsware.com/office-hours/ shortly

the next chat is Thursday at 7:30pm Eastern

have a pleasant day, all!

thank you, bye :)

you too!