Android :: Why Add Child Activities To TabActivity Instead Of Simply Using Views
Mar 17, 2010
I've been programming in Android for two years now and just joined an Android project where they are using a TabActivity to host multiple Activities. It's unclear why this is better than rewriting the TabActivity to simply use Views instead.
TabActivity extends ActivityGroup which means TabActivity can host both Activities and Views. But what's the use of this capability? I was under the impression that Activities should be treated as individual screens of an application.
In short, what is an example use case where it's recommended that TabActivity should host multiple Activities rather than multiple Views?
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Jan 6, 2010
I have a simple ListView and on that ListView I have placed a number of custom defined Views. The CustomView has ImageView and two TextViews.
The CustomView also has a "stateful drawable" as background, so that the background image (a 9-patch) changes if you press the Row in the ListView. When pressing the Row, the background image changes to a Red-ish thing.
The problem is that when the background changes from the default greyish, all the Views in the CustomView (ImageView and TextViews) still have their greyish background and thus creates very ugly greay boxes on top of the now redish background.
What is the best way to solve that problem? I hoped that such things were handled automatically (as it is done in for example .NET), but I was wrong it seems.
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Jul 25, 2010
I am using a TabActivity (Main) with 3 TabSpecs
I am using Intents for the content of the 3 Tabs
TabA, TabB, TabC for example.
All these tab activities use common data that is stored in SharedPreferences
In the Main TabActivity I have an options menu which has a refresh option.
CODE:.............
This refresh uses an AsyncTask (updateCommonDataFromWeb) to reload the common data from the web.
I need a way to tell the 3 tab activities to refresh their views and rebuild their content from the newly downloaded data.
When the tab activities are first created they load the data from SharedPreferences like so:
CODE:..............
I thought about making a common method on each of the tab activities
like.... reloadViewData()
I thought maybe I could use the activity manager from the Main TabActivity to get the activity of the current tab like so:
CODE:.............
Unfortunately i cant get this approach to work, whilst activity is the correct instance its an Activity instead of a TabA,TabB or TabC
Maybe i've completely taken the wrong approach to the whole thing.
I have also read alot about not using Activities for tab content instead using views.
However I dont know what view to use to replace my <RelativeLayout /> as i cant use my R.layout.* as views.
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Jan 25, 2010
Is there any way to query a root view of an activity for all of its child views even before the root view or its children have been inflated? I guess what I'm looking for is whether a view knows ahead of time what children it will have before it gets inflated, and can I get that list in some way. Bizarre I realize, but I think it will help me with some unconventional automation testing I'm working on. I haven't found anything in the API like this.
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Feb 10, 2009
I'm trying to implement my own ActivityGroup to mimic TabActivity (without tabs) but I'm having trouble "closing" activities.My ActivityGroup has a ViewFlipper, each housing a separate activity's window.When I attempt to switch "activities" I call ViewFlipper.setDisplayedChild() on the view of choice.However, when I scroll up and down in the view of choice, the OTHER non-visible activities' views are responding to these actions, so it seems like I'm not successfully "switching" the activity fully.When I use a TabActivity to run this code, this doesn't happen; when I scroll up and down in one activity, I don't see any event firing from any of the other activities. I'm wondering what does TabActivity do to handle these activities as separate, individual entities?
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Jul 8, 2010
In my app, I have 5 tabs which contains activities. In each of them, I have to show differents screens. For example, the main activity of a tab is a listview, and when I click on one of its item, I want to display a second screen with an other listview, that will display an other screen when the user will select an item etc.
So I knew that activities in tabs are not easy to manage, but I really think that I needed this solution. Indeed, each screen must contain a back button, which will return to the previous screen, with the previous state (the same position in the list).
To start new activities inside the tabs, I used the technique described here http://gamma-point.com/content/android-how-have-multiple-activities-under-single-tab-tabactivity
It works mostly well, but I encounter a problem to go back to the previous activities. My solution at the moment consists in starting the previous activity like it's described on this website, but without any flag.
So here are my two real problems:
When I try to go back to the first and main activity of the tab, it seems that a new instance is created, even if I use the flag Intent.FLAG_ACTIVITY_CLEAR_TOP. So when I do several roundtrips between this activity and the next one, i obtain a StackErrorOverFlow.
Because the activities are accessible from differents activities, I have to memorize the parents activities all the time, by giving them in the intents. It's really heavy when I have a succession of 5 or 6 screens, I have to memorize the grand grand parent if the activity... I really appreciate if I just could call the last Activity started by the localActivityManager.
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Oct 23, 2010
I am trying to figure out how to add a child view to a parent view so I can use the MotionEvent.ACTION_MOVE feature to move from one child view to the next. Is this possible?
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Sep 7, 2009
I am facing problem in fixing the child in particular place in views or layout.
1) Can I fix the child at the starting and ending of Layout directly?
2) Can I fix the child at the starting or ending of the view directly?
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Aug 29, 2010
I have a number of child views, each child is a TableRow and I need to be able to change the order of the TableRows, such that I can swap the rows into any order. I know there is a method called removeAllViews() but I don't really want to remove and re-create the views if its possible to access and change the order. I really want the display to update as smoothly as possible, taking the minimum amount of time, is it possible?
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Sep 20, 2010
i've got an ExpandableListView with my own layouts for the group and child views. a certain group-type will require a different layout. is that possible - i.e. a ELV with different layouts for a group view. i've got my own sub-class of SimpleExpandableListAdapter.
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Jun 8, 2010
Is it possible to give Focus on listitem chile views , what i need is i have an custom list view , i creating each row using linear layout with two views like button and textview, now i want to get that button click event and have to change the background color while focusing is it possible?
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Aug 31, 2010
Can someone help me with my Syntax/Methodology? I would like to set up a bunch of different views in a viewgroup. My code fails at the addView method.
Unfortunately, I can't find jack for examples (which is how I learn) using the ViewGroup class online.code...
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Feb 28, 2010
ExpandableListView has a setOnChildClickListener method, but lacks of setOnChild*Long*ClickListener method.
When I added setOnLongClickListener() on child view in getChildView(), whole sublist became completely unclickable (despite of parentView.setOnChildClickListener() present and working before).
How can I enable long clicks on child views?
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Sep 27, 2009
I need a LinearLayout to contain 3 TableLayouts, and I can't get it to work. This is where the problem is I'm sure:
mTableLayout.addView(mLinearLayout, LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT); mLinearLayout.addView(nTableLayout, LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT); mLinearLayout.addView(oTableLayout, LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT); mLinearLayout.addView(pTableLayout, LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
How Do I make this work? I can get it to work just find when I only add a single child view, but when I have multiple children view objects my app crashes.
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Apr 19, 2010
When using a View within a View, for example an ImageView within a LinearLayout, both of which have xml drawable resources (the LinearLayout as a background) specifying PNG drawables to use for the on/off states, shouldn't children Views receive the focus state when their parent gets focus? So as far as I understand, both my LinearLayout and ImageView should be switching to their focus states right? Apparently not Or, more likely, apparently my implementation is incorrect.
The focus state works on the LinearLayout but my ImageView never receives focus.. I have both Views set to android:focusable="true".
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May 6, 2009
I am trying to create an activity layout that has a top level vertical linear layout like so:
CODE:................
This works ok as long as the wordDefinition text isn't very long. But, when I set the text to something very long, it pushes the back button off the bottom of the screen. Why? Isn't the ScrollView supposed to scroll the text in the child TextView?
I've tried playing with weights (e.g., giving the top text view a weight of .2, the scroll view a weight of .7 and the button a weight of .1, but to no avail.
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Jul 8, 2010
I am working on an Android app that has multiple screens the user will need to navigate between and I am curious what the best practices are when switching between those screens. I am torn between creating a new Activity for each screen and simply changing the view (setContentView(R.layout.whatever)). The screens all share at least some variable values so I'm leaning toward changing views and using class level variables, but I'm worried a single activity could become very large and confusing with logic for multiple screens in a single file. I'd like to keep the code clean and separated, but I also don't want to be passing several variables around between views if that isn't needed.Being new to Android development, I'm hoping some more experienced members of the community could share their thoughts and let me know how best to handle it
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Aug 3, 2010
I start a browser and from the browser,I start a video which occupies only a small part of the screen,say the bottom right corner.
Now the browser will be pushed to the 2nd position in the window order and Video will come to the first position. Is it possible that browser can have the control for active window and receive the key events though the video is the Top Most window.
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Apr 24, 2009
I've got a activity showing the user a list of songs to play, and when he opens a song I launch an activity which embed a player.
My problem is that when i finish playing i call "this.finish()", but when the user reopen the player, the "onCreate" is launched and it seems that the GUI is building itself "again".
I've tried to not call "this.finish()" and call the Activity.startActivity on the father, but with this way, when I clic on the "back" button on the emulator, I get all the players playing in the same time (they still exist).
So my question, is there a way to make an activity "a singleton" or to freeze it to be retrieved later (It can't be able to retrieve it with "back" button) or a way to cache all the constructions so to not have to do it again ?
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Jul 16, 2010
I am developing a Music Player and I have a view flipper to control all the artist view, album view, so on and so forth. What I am doing now is that I have list view in each view of the view flipper. However, I do not want to put all my codes inside one activity but rather, to have different activities for each view. Is that possible to implement?
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Jul 31, 2010
My situation is the following: I have written one MapActivity class that is able to display a set of places as well as single places. On startup, the application creates an instance of this MapActivity and displays multiple places. If the user clicks on a certain place, then a new Activity is launched that shows the details of the selected place. This activity has a menu item that allows the user to view the place on a map - this causes that a new instance of the MapActivity is created, except that now only this single place is displayed.
The problem now is that if the user navigates back to the first MapActivity (the one that shows multiple places) the tiles won't be loaded anymore + sometimes OutOfMemoryErrors are encountered. According to the Android JavaDocs, it is only possible to have one MapActivity per process. However, I don't want to define my MapActivity as a singleInstance/singleTask, since the user should always be able to navigate back to the first MapActivity that shows multiple places. I have seen that the Google Places app (which has come with Google Map 4.4) for Android uses multiple MapActivity instances. How is this possible?
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Sep 13, 2010
Trying to understand the Android framework model. I have an application that needs to have several threads running. On thread gets GPS fixes, another picks up GPS fixes and pushes them to server, and yet another occasionally polls a server for dispatched orders. Some of these threads update status Views as well.
Since I am new to Android, the application framework model hasn't clicked for me. Where are these threads started? Right now I start the threads in the initial Activity, but if I understand it right, once that Activity goes invisible it is stopped. Furthermore, I have to track GPS and network statistics so that I can have a View which may (or may not) be the active View.
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Jun 10, 2010
I am attempting to learn how to develop on the Android platform but do not quite understand the relationship between Activities and Views, because according to the documentation an Activity is almost always linked to a UI object that the user can interact with, but if this is the case where does the whole idea of Views come in?
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Jan 15, 2010
I have developed some apps for Android, and this questions stays always:
How should I structure my UI? Should I launch activity after activity and leave the phone to make the "back" button, or should I choose more optimized, but more complex to implement, way with switching manually Views and then manually doing the "Back" button functionality?
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Jul 15, 2009
Here is my screen description: It is a TableLayout and it contains multiple Rows. I have set TableRow as clickable, as I want to go to next screen on click of a tableRow. Everything I am doing through Java programming (instead of XML layout, because number of TableRows changes each time) On next screen, I wanted to display all the views of that particular clicked TableRow. Here the problem i am facing is how to capture particular tableRow on onclick() even and how do I get all the textviews of that particular Row. I tried to set id at runtime, and tried to get id of view, but it's not working, giving error resourcenotfoundexception.
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Aug 16, 2010
Are there design guidelines to help decide if an application with multiple views should be designed with multiple activities or just one activity and control the back button itself.
I've tried both. My most complex applications using one activity per screen. However, now that I'm successfully written an app with just one activity and handling the back button myself, I don't see any compelling reason to use multiple activities. The one activity application is much simpler and more straightforward.
What advantages of multiple activities am I missing?
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Feb 18, 2010
I'm working on an application using xml layouts.
I wish to know which is better:
1. Use few activities and change its contentview
2. Use an activity for each 'view' needed
If both works, in which case which option would be better?
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Nov 16, 2010
I am implementing a music player application in Android. My play list selection screen is implemented as a tab selector widget which contains a ListActivity inside each of the tabs: Artist, Albums, Songs.
I want to update the ListView in each of the ListActivity when I delete an item from any of the lists.
i.e. When I long press an item in the Artists list a context menu is drawn with "Delete Artist"
And it should delete all the songs from this artist in the Songs ListView, delete all the albums by this artist in the Albums ListView, and finally delete the entry for the artist in the Artist ListView.
Each of the ListActivity has its own fillData() method, which updates the ListView when the button in the context menu is pressed.
How can I call the fillData() method of the Albums ListActivity after I update the ListView inside of the Artists ListActivity?
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Feb 28, 2010
I want to populate a table, defined in layout xml file through the programmatic way. I have define Table with a single row defining its header, with all the attributes set. Now i want to know a way so that i can just replicate that header row in the table with new content.
I tried using inflator inflate(int,view) method, but at runtime it showed up with error.
Here is the XML code for the layout file defining the table
CODE:.................
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Mar 6, 2010
I have the following XML code:.................
The idea is to change the views, whenever I press one of the radio buttons. When I press a button the first time everything works out fine, but the second time I press a button, I get an IllegalStateException, and I can't quite see why I'm getting this.
Also, the Activity seems to set all my global variables to null, which is why I have to create them every time I switch from portrait to landscape or vice versa. So I would like to know if there is a way I can save my views in the Bundle, or any other way in which I can permanently save my views, so I don't have to add or create them every time, I flip the phone. And whenever I flip the phone, it seems that it rereads the main XML file, causing the RadioGroup to be set to 2D even if the 3D button is checked. This is because I've said the 2D button to be checked from when the app is first created, but I would like to also save the state of that RadioGroup.
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