[Pager] Re-write Pager on top of LazyRow|Column

sample/src/main/AndroidManifest.xml

@@ -126,6 +126,17 @@
             </intent-filter>
         </activity>
 
+        <activity
+            android:name=".pager.HorizontalPagerLoopingSample"
+            android:label="@string/horiz_pager_title_looping"
+            android:exported="false">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="com.google.accompanist.sample.SAMPLE_CODE" />
+            </intent-filter>
+        </activity>
+
+
         <activity
             android:name=".pager.HorizontalPagerTabsSample"
             android:label="@string/horiz_pager_title_tabs"

sample/src/main/java/com/google/accompanist/sample/pager/HorizontalPagerLoopingSample.kt

@@ -0,0 +1,110 @@
+/*
+ * Copyright 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.accompanist.sample.pager
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.aspectRatio
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.material.MaterialTheme
+import androidx.compose.material.Scaffold
+import androidx.compose.material.Surface
+import androidx.compose.material.Text
+import androidx.compose.material.TopAppBar
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.unit.dp
+import com.google.accompanist.pager.ExperimentalPagerApi
+import com.google.accompanist.pager.HorizontalPager
+import com.google.accompanist.pager.rememberPagerState
+import com.google.accompanist.sample.AccompanistSampleTheme
+import com.google.accompanist.sample.R
+
+class HorizontalPagerLoopingSample : ComponentActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+
+        setContent {
+            AccompanistSampleTheme {
+                Surface {
+                    Sample()
+                }
+            }
+        }
+    }
+}
+
+@OptIn(ExperimentalPagerApi::class)
+@Composable
+private fun Sample() {
+    Scaffold(
+        topBar = {
+            TopAppBar(
+                title = { Text(stringResource(R.string.horiz_pager_title_looping)) },
+                backgroundColor = MaterialTheme.colors.surface,
+            )
+        },
+        modifier = Modifier.fillMaxSize()
+    ) {
+        Column(Modifier.fillMaxSize()) {
+            // Display 10 items
+            val pageCount = 10
+
+            // We start the pager in the middle of the raw number of pages
+            val startIndex = Int.MAX_VALUE / 2
+            val pagerState = rememberPagerState(initialPage = startIndex)
+
+            HorizontalPager(
+                // Set the raw page count to a really large number
+                count = Int.MAX_VALUE,
+                state = pagerState,
+                // Add 32.dp horizontal padding to 'center' the pages
+                contentPadding = PaddingValues(horizontal = 32.dp),
+                // Add some horizontal spacing between items
+                itemSpacing = 4.dp,
+                modifier = Modifier
+                    .weight(1f)
+                    .fillMaxWidth()
+            ) { index ->
+                // We calculate the page from the given index
+                val page = (index - startIndex).floorMod(pageCount)
+                PagerSampleItem(
+                    page = page,
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .aspectRatio(1f)
+                )
+            }
+
+            ActionsRow(
+                pagerState = pagerState,
+                modifier = Modifier.align(Alignment.CenterHorizontally)
+            )
+        }
+    }
+}
+
+private fun Int.floorMod(other: Int): Int = when (other) {
+    0 -> this
+    else -> this - floorDiv(other) * other
+}

sample/src/main/res/values/strings.xml

@@ -26,6 +26,7 @@
     <string name="horiz_pager_title_basics">Horizontal Pager: Basic</string>
     <string name="horiz_pager_with_indicator_title">Horizontal Pager: Indicator</string>
     <string name="horiz_pager_with_transition_title">Horizontal Pager: Transition</string>
+    <string name="horiz_pager_title_looping">Horizontal Pager: Looping</string>
     <string name="horiz_pager_title_tabs">Horizontal Pager: Tabs</string>
     <string name="horiz_pager_title_scroll_content">Horizontal Pager: Scrolling content</string>