Develop Reference

Are too many views in XML bad?

I have an XML file with about 150 views. Yes, I know it is a lot and I did get a message from Android Studio saying I can't exceed 80 views. But I can't drop views any lower than 150. I considered using list view but it works the way I wanted it to.
The question is, will this many views make the app crash/slow the device? I've tried it on my s7 and it works perfectly fine. My lowest API is 17 which is 4.2. Wouldn't 4.2 devices be able to handle this XML without any problem?
Thanks.

The problem with having an excessively large number of Views is that Android often needs to measure, layout, and draw them, and it will traverse the entire View hierarchy to do this. If the number of Views is so large that this traversal takes more time than the screen refresh rate, you will skip frames and your UI might appear to lag or be choppy.
If not all of those Views need to be on screen at once (for example, if you are using a ScrollView to hold a very large container that the user can scroll through), then you should probably switch to using RecyclerView.
If all of those views need to be on screen at once, then you might consider writing custom Views that can display your content all at once instead of having individual Views that draw individual things. This can drastically reduce the time and complexity of the measure/layout/draw traversals.
It's difficult to suggest an approach without knowing more specifics about your UI, but hopefully that explains the issue.

How to do an infinite horizontal sliding scroll of images on Android using Delphi XE 5?

We want to show in an Android app a list of images in the similar manner with many gallery apps: horizontal sliding by using a gesture to show the next/previous image.
Also the image viewer should support zoom/pinch (besides other features).
Images can came from a database or from a directory and can be as much as 200-300.
The question is: Which is the best way to implement the slide-show part from the environment described above?
Through animations of a two TImage? There exist a specialized component for this? By using Horizontal Scroll box?

Stick 10 TRectangle objects in a THorzScrollBox. It could be more or less than 10 depending on the memory that the device has. Align them all to alTop. Load the images for display in TRectangle.Fill.Bitmap.Bitmap.
When the user scrolls down and is near the bottom of the ten, move the top rectangle to the bottom of the chain and load the newest image from your list into the new bottom one.
When the user scrolls up and is near the top of the ten, move the bottom rectangle to the top of the chain and load the newest image from your list into the new top one.
The reason behind doing it this way is that TRectangle is a really light image display container and you are recycling the TRectangle objects instead of deleting and creating them all the time.
It is possible that you will experience a display pop when you move the next TRectangle object to the top of the chain or when you move it to the bottom of the chain. You will have to create code to take care of this either by setting the position on THorzScrollBox or decreasing and increasing the height of the TRectangle as it leaves or enters the view until it is full size.

If you have installed samples with your Delphi instalation then you can find several examples of how to do this in:
Samples\FireMonkey\Fireflow
Samples\FireMonkey\MetropolisUIFlipViewDemo
Maybe there are even more of them. I haven't checked every sample so far.

How is the number of views limited?

I want to figure out the main effectivity issues of the Android layouts and views. I'm doing a research now but maybe somebody has answers already.
I have a RelativeLayout that is populated with views dynamically. Basically, the application loads a forum thread in XML and then renders the discussion tree so each message is displayed in its own group of views. I've decided not to use WebView because I want to implement some client-side functions that should be easier to do on custom views than on HTML page.
However this approach has a major flaw: it's heavy.
The first problem (which I've solved) was nesting of views. This is not an issue now, my layout is almost flat so the maximum depth is 10-12 (counting from the very top PhoneWindow$DecorView, the actual depth depends on data).
Now I've reached the next limit that is somehow connected to (or caused by) resource consumption of the views. After loading the data, the application hangs for a while to build the layout (creates the views and populates them with the data), and the hang time seems to grow linear with the data size; and if the data is large enough, the view will never appear (eventually the system suggests closing the application because it isn't responding).
Now the questions:
Does memory consumption depend significantly on the view class? In other words, is there any major difference between a Button and a TextView, or an ImageView? I can attach a click handler to any view so they don't differ much in usage.
Do background images affect the performance? If the same image is set in N views, will it make the layout N times heavier? (I understand that this question may look silly but anyway.)
Are nine-patch images significantly heavier than regular ones? What is better: to create N views where each has some background images, or to make one view that is N times wider and has a repeating background?
Given some layouts, what should be optimized first: overall number of views, nesting levels, or something else?
The most interesting. Is that possible to measure or at least estimate the resources consumed by the activity and its views? If I make some change, how could I see that I'm going the right way?
UPDATE
Thanks to User117, some questions that I asked above are now answered. I've used the Hierarchy Viewer and optimized my layout: compared to what I had before, the overall number of views is now reduced almost twice, and the nesting is also reduced.
However the application still hangs on a large forum thread.
UPDATE 2
I've connected the debugger to my device and found that the application gets out of memory.
But what is very unexpected for me is that the error occurs after I populate the layout. The sequence is as follows:
All my views are added. I can see a slight slow down as they are being added.
Almost nothing happens for a couple of seconds. During that time, a few info messages are spawned in the log, they are identical: [global] Loaded time zone names for en_US in XXXXms, the only difference is number of milliseconds.
The out of memory error message is spawned: [dalvikvm-heap] Out of memory on a N-byte allocation (the actual size varies). The long error reporting starts.
What does this mean? Looks like the rendering have its own demands that may be considerable.
UPDATE 3
At last I've found the core issue. Here is a screenshot from my application, see an explanation below the image.
Each message consists of a round button that shows or hides the replies and a red content frame to the right of the button. This is very simple and requires only 6 views including the layouts.
The problem is the indentation with these connection lines that show which message is related to which.
In my current implementation, the indentation is built of small ImageView's, each containing a square image that shows either empty space, or a vertical line, or a T-like connector, or a L-like corner. All these views are aligned to each other within the large RelativeLayout that holds the whole discussion tree.
This works fine for small and medium trees (up to few hundreds of messages), but when I try to load a large tree (2K+ messages), I get the result explained in UPDATE 2 above.
Obviously, I have two problems here. I spawn large number of views that all consume memory, and these views are ImageView's that require more memory for rendering because they render a bitmap and therefore create graphics caches (according to explanation given by User117 in the comments).
I tried disabling loading the images into the indentation views but got no effect. It seems like adding that huge number of views is quite enough to eat all available memory.
My other idea was to create an indentation image for each message that would contain all pipes and corners, so each message would have the only indentation view instead of 10 or 20. But this is even more consuming: I've got out of memory in the middle of populating the layout. (I cached the images in a map so two bitmaps with identical sequence of images weren't created, that didn't help.)
So I'm coming to conclusion that I'm in a dead end. Is it ever possible to draw all these lines at once?

Different View's are different kinds of Object. Some only draw() light weight stuff, some can hold large Bitmap Objects, and handler Objects and so on. So, yes different View's will consume different amount of RAM.
If same Bitmap object is shared among views, There's only one Object in RAM, each View will have a reference variable pointing to that object. But, not so when View draws: Drawing same Bitmap n times at n places on screen will consume n times CPU and generate n different bitmap_cache for each View.
Each side of a 9-patch image is actually bigger by 2 pixels from the original image. They are not much different as a file. When they are drawn, both can be scaled and will take almost equal space. The only difference is that 9-Patch are scaled differently.
Setting the background of the larger, parent view is better when the child views are transparent, and background will show through.
You can save a small image and set a tiled background so that it can fill a large area.
Nesting is to be optimized first, because all of the views might not be visible at a given time, let's say only a few views are visible in scrolling layout. Then you can cut down on total number of views used. Take cues from ListView: Given that user will be only seeing a sub set of total data at a time, it re-cycles the views. and saves a lot of resources.
SDK provides Hierarchy Viewer tool for this purpose. It shows a full tree structure of a running Layout, also places red flags for the sluggish parts of the layout.
A good layout is that which:
Easy to be measured (avoid complex weighted widths, heights and alignments). For
example instead of doing layout_gravity="left" for each each child, parent can have gravity="left".
Has less depth, each overlapping view adds another layer to be composited while screen is drawn. Each nested View Structure, asks for a chained layout call.
Is smart and re-cycles Views rather than create all of them.
Reuses its parts: tags like <merge> and <include>.
Update:
Answers to this question, show many approaches for a tree view in android.

Create large content grid in Android

I want to create a large grid for a android phone application where the size of the grid may vary from e.g. 10x10 to up to around 300x300. The content of each cell will be a test and some background (grid will eventually become skinnable).
I developed this earlier for iOS using UIScrollView and CATextLayers for labels, where the cells' content were loaded/unloaded based on their distance from the the visible section of the screen so that memory-wise it was always within a decent range.
What is the equivalent to this in Android applications?
I will be developing for 2.3 (and later for 4.0) and it should run both on phones and on tablets.

Some info before making a decision:
While in iOS UIScrollView goes in both axis, android's ScrollView just go in one direction.
In Android you have a GridView, but, once again, I don't think you can scroll in both axis.
In Android, widgets that work like a UITableView needs an Adapter that takes care of creating each of the views.
If I were you I would start reading:
How androidbigimage project handles the scrolling through all the screen.
How the GridView positions it's item in a grid and how it handles the variation of the grid size.
Once you get all that info, create a custom view similar to the GridView and start placing items using an Adapter.
PS: When you finish it, make it open source :)

Need to create spreadsheet like control, what should I extend ListView or GridView?

I am an experienced developer, but I'm inexperienced on the Android platform. So I am seeking some advice from developers with more experience with Android.
I am building a Honeycomb application using Fragments. One of the fragments calls for a vertically scroll-able read-only "HTML table-like" view with dynamically loaded data. Similar to a spreadsheet, I should have clickable headers which I can implement server-side requests to filter/sort the data.
I am pretty sure this Control doesn't exist yet, am I right? Do I have to build it?
Assuming I have to build it, which existing widget should I extend? ListView, Table, GridView?
I assume I would have one widget for the header, and then wrap the body of the table in a scrollable layout to handle scrolling while keeping the header visible. I am concerned that I might not be able to guarantee that the headers line up with the columns.
Thanks in advance,
Tim

Android layouts are pretty basic - there are not any shipped layouts that will really do what you are looking for automatically, but you could probably do what you want with a heavily controlled gridView. Android is also pretty bad about controlling multiple elements to fit within the screen size, as it's goal is to support multiple screen sizes and densities.
From what I understand your desire to be, I think the best solution is to create a nx2 grid view dynamically, and control the width of the view based on the device size. You would have n number of headers on the top, and you could fill the lower half of the grid with your textViews, or whatever data you wanted. The hard part would be keeping the widths of the grid elements under control and on the screen. In addition, you will probably find that you can only fit a small number of header items on the screen because of the phone's small size, so you may discover a better layout to fit your needs.