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 b90079595f33f58fece04026a97faa0d243acdb1
Author: Yuichi Araki <yaraki@google.com>
Date: Wed Sep 18 16:55:49 2019

Change the way to detect mismatch between POJO and query

This fixes cursor mismatch warnings with expandProjection.

Bug: 140759491
Test: QueryMethodProcessorTest
Change-Id: I7659002e5e0d1ef60fc1af2a625c0c36da0664d8

M room/compiler/src/main/kotlin/androidx/room/processor/QueryMethodProcessor.kt
M room/compiler/src/main/kotlin/androidx/room/solver/TypeAdapterStore.kt
M room/compiler/src/main/kotlin/androidx/room/solver/query/result/PojoRowAdapter.kt
M room/compiler/src/test/kotlin/androidx/room/processor/QueryMethodProcessorTest.kt
M room/compiler/src/test/kotlin/androidx/room/testing/TestProcessor.kt

https://android-review.googlesource.com/1123258

https://goto.google.com/android-sha1/b90079595f33f58fece04026a97faa0d243acdb1

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

The following changes were cherrypicked through Coastguard (

https://android-build.googleplex.com/coastguard/)
Release Track: (

https://android-build.googleplex.com/coastguard/dashboard/6093116828680192/#/cherrypickHistory/all)
Created: 2019-10-14 17:23:42.610596+00:00
Changes: aosp/1123258

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

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

commit bdde5a1a970ddc9007b28de4aa29d60ffa588f08
Author: Yigit Boyar <yboyar@google.com>
Date: Thu Apr 16 16:47:05 2020

Re-factor how errors are dismissed when query is re-written

This CL changes how we handle errors/warnings if query is
re-written.
There was a bug in expandProjection where we would report warnings
for things that Room already fixes automatically (

b/140759491

).
The solution to that problem (I7659002e5e0d1ef60fc1af2a625c0c36da0664d8)
solved it by deferring validating of columns until after re-write
decision is made. Unfortunately, this required changing PojoRowAdapter
to have a dummy mapping until it is validating, make it hard to use
as it does have a non-null mapping which is not useful.

This CL partially reverts that change and instead rely on the log
deferring logic we have in Context. This way, we don't need to break
the stability of PojoRowAdapter while still having the ability to
drop warnings that room fixes. This will also play nicer when we
have different query re-writing options that can use more information
about the query results.

Bug: 153387066
Bug: 140759491
Test: existing tests pass
Change-Id: I2ec967c763d33d7a3ff02c1a13c6953b460d1e5f

M room/compiler/src/main/kotlin/androidx/room/log/RLog.kt
M room/compiler/src/main/kotlin/androidx/room/processor/QueryMethodProcessor.kt
M room/compiler/src/main/kotlin/androidx/room/solver/TypeAdapterStore.kt
M room/compiler/src/main/kotlin/androidx/room/solver/query/result/PojoRowAdapter.kt

https://android-review.googlesource.com/1288456

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