Feature request: Document how to display an empty screen [159054196]

Fixed

Bug

Status Update

No update yet.

Description

ri...@soundcloud.com

created issue #1

Jun 16, 2020 09:13AM

The doc about how to load and display paged data with Paging 3.0 clearly explains how to show progress and error views but it doesn't cover how to handle the case of an empty result. Also the samples seem to not support that case.

I'm new to the Paging library and I find it non trivial to determine what is the right LoadingState to listen to. I assume it's the refresh state, but even there it's not clear how to determine whether the result is empty or not.

Maybe this suggestion should go to a separate issue but I think it would be nice to reuse the same LoadStateAdapter approach as that would allow to build nice reusable loading-empty-error page components.

Comments

le...@gmail.com <le...@gmail.com> #2Jun 16, 2020 01:29PM

Project: platform/frameworks/support
Branch: androidx-master-dev

commit c60f33e229e31ab328ef6b59dab63b264954831c
Author: Alexandre Elias <aelias@google.com>
Date: Fri Jul 10 16:23:09 2020

Semantics no-op cleanups

Partly in response to lmr's broad code review, I did a pass of
superficial API/implementation cleanup. The main changes are:

- I changed each Boolean SemanticsProperty where false is equivalent to
not being present to take "Unit" instead. This is conceptually
clearer: it avoids questions like "can I cancel out a semantics from a
merged child by setting it to false?" Because "property = Unit" looks
weird, I also changed the style of these to "property()".

- I moved the Semantics id generator closer to where it's used, in
SemanticsModifierCore. I made it internal and an AtomicInt.
(Note that integer ids are heavily used in the Android
AccessibilityNodeInfo APIs so I can't simply remove them entirely.)

- I deleted dead code. Some examples include SemanticsHintOverrides,
a public API not connected to anything, and SemanticsPropertyKey
merge() open method which is never called. (In both cases I have
a different plan in mind for accessibility.)

Fixes: 145951226
Fixes: 145955412
Test: existing tests
Relnote: "Single-value semantics properties now use a calling style.
For example, 'semantics { hidden = true }' is now written as:
'semantics { hidden() }'."

Change-Id: Ic1afd12ea22c926babc9662f1804d80b33aa0cfc

M ui/integration-tests/benchmark/src/androidTest/java/androidx/ui/benchmark/test/LayoutNodeModifierBenchmark.kt
M ui/ui-core/api/0.1.0-dev15.txt
M ui/ui-core/api/current.txt
M ui/ui-core/api/public_plus_experimental_0.1.0-dev15.txt
M ui/ui-core/api/public_plus_experimental_current.txt
M ui/ui-core/api/restricted_0.1.0-dev15.txt
M ui/ui-core/api/restricted_current.txt
M ui/ui-core/src/androidAndroidTest/kotlin/androidx/ui/graphics/vector/VectorTest.kt
M ui/ui-core/src/androidAndroidTest/kotlin/androidx/ui/semantics/SemanticsTests.kt
M ui/ui-core/src/androidMain/kotlin/androidx/ui/core/AndroidActuals.kt
M ui/ui-core/src/androidMain/kotlin/androidx/ui/core/AndroidComposeView.kt
M ui/ui-core/src/androidMain/kotlin/androidx/ui/core/AndroidComposeViewAccessibilityDelegateCompat.kt
M ui/ui-core/src/androidMain/kotlin/androidx/ui/core/AndroidPopup.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/Expect.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsConfiguration.kt
D ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsHintOverrides.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsModifier.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsNode.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsOwner.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsWrapper.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/semantics/SemanticsProperties.kt
M ui/ui-foundation/api/0.1.0-dev15.txt
M ui/ui-foundation/api/current.txt
M ui/ui-foundation/api/public_plus_experimental_0.1.0-dev15.txt
M ui/ui-foundation/api/public_plus_experimental_current.txt
M ui/ui-foundation/api/restricted_0.1.0-dev15.txt
M ui/ui-foundation/api/restricted_current.txt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/Clickable.kt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/Dialog.kt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/Scroller.kt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/selection/Selectable.kt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/selection/Toggleable.kt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/semantics/FoundationSemanticsProperties.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/ButtonTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/CardTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/CheckboxScreenshotTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/RadioButtonScreenshotTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/ScaffoldTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/SnackbarTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/SurfaceTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/ripple/RippleIndicationTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/textfield/TextFieldScreenshotTest.kt
M ui/ui-material/src/main/java/androidx/ui/material/AppBar.kt
M ui/ui-material/src/main/java/androidx/ui/material/TextFieldImpl.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/AssertsTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/CallSemanticsActionTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/ErrorMessagesTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/FindersTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/PrintToStringTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/ScrollToTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/TextActionsTest.kt
M ui/ui-test/src/main/java/androidx/ui/test/Actions.kt
M ui/ui-test/src/main/java/androidx/ui/test/Filters.kt
M ui/ui-text/api/0.1.0-dev15.txt
M ui/ui-text/api/current.txt
M ui/ui-text/api/public_plus_experimental_0.1.0-dev15.txt
M ui/ui-text/api/public_plus_experimental_current.txt
M ui/ui-text/api/restricted_0.1.0-dev15.txt
M ui/ui-text/api/restricted_current.txt
M ui/ui-text/src/commonMain/kotlin/androidx/ui/text/CoreTextField.kt
M ui/ui-text/src/commonMain/kotlin/androidx/ui/text/TextSemanticsProperties.kt

https://android-review.googlesource.com/1360099

du...@google.com <du...@google.com> #3Jun 16, 2020 03:14PM

Thanks for this, this is something we are definitely interested in! As a workaround, you can check adapter.itemCount.

cc...@google.com <cc...@google.com> #4Jun 16, 2020 04:06PM

We have a sample snippet showing how to use adapter.itemCount in this way, but forgot to link it in KDocs (whoops): https://cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:paging/samples/src/main/java/androidx/paging/samples/PagingDataAdapterSample.kt;l=141;drc=dd7a076c68069bec9477ca7295562fcd794e696b

Will fix.

du...@google.com <du...@google.com> #5Jun 16, 2020 04:30PM

To be clear, adapter.itemCount will only work if placeholdersEnabled is false.

We held off on this change because we wanted to take some time to properly explore what it would look like to provide a public API to view the PagingState or the internal PageEvent stream, but it's clear there's immediate need for this.

In the meantime, here's an idea for a CL which adds a Boolean to dataRefreshFlow, which we could merge for alpha02: https://android-review.googlesource.com/c/platform/frameworks/support/+/1339857

ap...@google.com <ap...@google.com> #6Jun 16, 2020 04:48PM

Project: platform/frameworks/support
Branch: androidx-master-dev

commit 0deeb4e05177350b8c2b444e6db418b9fc7aa66b
Author: Chris Craik <ccraik@google.com>
Date: Tue Jun 16 08:26:09 2020

Actually link addLoadStateListenerSample in kdocs

Bug: 159054196
Test: Ctrl-Q in Studio

Change-Id: Ieabb25de3625a22f8107f1192af54e986a50d1d3

M paging/runtime/src/main/java/androidx/paging/PagingDataAdapter.kt

https://android-review.googlesource.com/1339856

cc...@google.com <cc...@google.com> Jun 16, 2020 05:11PM

Reassigned to du...@google.com.

ap...@google.com <ap...@google.com> #7Jun 17, 2020 11:33PM

Marked as fixed.

Project: platform/frameworks/support
Branch: androidx-master-dev

commit 38a9eb05e73e822f70348aa22264b36e6790dba8
Author: Dustin Lam <dustinlam@google.com>
Date: Tue Jun 16 09:24:15 2020

Add isEmpty param to dataRefreshFlow / listener

RelNote: "The adapter APIs, dataRefreshFlow and dataRefreshListener
now pass a Boolean to signal whether a PagingData is empty"
Fixes: 159054196
Test: ./gradlew paging:paging-runtime:cC

Change-Id: I6e37e844cf9f947aeefaaa99d22b2672e04f207d

M paging/common/src/main/kotlin/androidx/paging/PagingDataDiffer.kt
M paging/common/src/test/kotlin/androidx/paging/PagingDataDifferTest.kt
M paging/runtime/api/3.0.0-alpha02.txt
M paging/runtime/api/current.txt
M paging/runtime/api/public_plus_experimental_3.0.0-alpha02.txt
M paging/runtime/api/public_plus_experimental_current.txt
M paging/runtime/api/restricted_3.0.0-alpha02.txt
M paging/runtime/api/restricted_current.txt
M paging/runtime/src/main/java/androidx/paging/AsyncPagingDataDiffer.kt
M paging/runtime/src/main/java/androidx/paging/PagingDataAdapter.kt

https://android-review.googlesource.com/1339857