功能实现：新增“加载全部内容”场景

zengke328 · Jul 9, 2021 · 94cf757 · 94cf757
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diff --git a/README.md b/README.md
@@ -311,6 +311,12 @@ WanJetpack
             - [AndroidSwipeLayout](https://github.com/daimajia/AndroidSwipeLayout)
             - [SwipeRecyclerView](https://github.com/yanzhenjie/SwipeRecyclerView)
             - [Android 简单易上手的下拉刷新控件](https://www.jianshu.com/p/459e611c0f62)
+- 加载状态的几个场景：下拉刷新、上拉加载更多、底部的已加载全部内容、首次进入页面的加载状态（及加载失败提醒）
+    - 下拉刷新、上拉加载更多：略
+    - 首次进入页面的加载状态：
+    - 底部的已加载全部内容：方案比较多，个人比较倾向下面两种方案
+        - 方案一：通过withLoadStateFooter实现，和上拉加载更多用同一套布局，同一个adapter。【参考本demo】
+        - 方案二：通过ConcatAdapter.addAdapter实现，专门显示加载更多
 
 - Animation 动画： 下拉刷新场景通过属性动画实现
     - [官方文档](https://developer.android.google.cn/training/animation)

diff --git a/app/src/main/java/com/longjunhao/wanjetpack/adapter/FooterAdapter.kt b/app/src/main/java/com/longjunhao/wanjetpack/adapter/FooterAdapter.kt
@@ -1,11 +1,7 @@
 package com.longjunhao.wanjetpack.adapter
 
-import android.util.Log
 import android.view.LayoutInflater
 import android.view.ViewGroup
-import android.widget.Button
-import android.widget.ProgressBar
-import android.widget.TextView
 import androidx.core.view.isVisible
 import androidx.paging.LoadState
 import androidx.paging.LoadStateAdapter
@@ -23,43 +19,60 @@ class FooterAdapter(
     private val retry: () -> Unit
 ) : LoadStateAdapter<FooterViewHolder>() {
 
-    override fun onCreateViewHolder(
-        parent: ViewGroup,
-        loadState: LoadState
-    ) = FooterViewHolder(parent, retry)
+    override fun onCreateViewHolder(parent: ViewGroup, loadState: LoadState) =
+        FooterViewHolder(
+            ListItemFooterBinding.inflate(
+                LayoutInflater.from(parent.context),
+                parent,
+                false
+            ),
+            retry
+        )
 
-    override fun onBindViewHolder(
-        holder: FooterViewHolder,
-        loadState: LoadState
-    ) = holder.bind(loadState)
+    override fun onBindViewHolder(holder: FooterViewHolder, loadState: LoadState) {
+        holder.bind(loadState)
+    }
+
+    /**
+     * 1. 如果直接返回true的话，首次进入界面加载时，会执行两次网络请求，且RecyclerView会向下滚动一段距离。
+     *    所以需要加上loadState.endOfPaginationReached= true的条件。
+     *
+     * 2. 注意is的优先级比||、 &&的优先级高，所以：
+     *    a is b && c 是 (a is b) && c 的意思
+     *    a is b || c 是 (a is b) || c 的意思
+     *
+     */
+    override fun displayLoadStateAsItem(loadState: LoadState): Boolean {
+        return loadState is LoadState.Loading
+                || loadState is LoadState.Error
+                || (loadState is LoadState.NotLoading && loadState.endOfPaginationReached)
+    }
 }
 
 class FooterViewHolder(
-    parent: ViewGroup,
+    val binding: ListItemFooterBinding,
     retry: () -> Unit
-) : RecyclerView.ViewHolder(
-    LayoutInflater.from(parent.context)
-        .inflate(R.layout.list_item_footer, parent, false)
-) {
-    private val binding = ListItemFooterBinding.bind(itemView)
-    private val progressBar: ProgressBar = binding.progressBar
-    private val errorMsg: TextView = binding.errorMsg
-    private val retry: Button = binding.retryButton
-        .also {
-            it.setOnClickListener { retry() }
+) : RecyclerView.ViewHolder(binding.root) {
+
+    init {
+        binding.retry.setOnClickListener {
+            retry()
         }
+    }
 
-    /**
-     * todo 遗留问题：当所有数据都加载后，应该在FooterView上显示“已经到底了”之类的。
-     */
     fun bind(loadState: LoadState) {
-        Log.d("FooterAdapter", "bind: ljh loadState=$loadState")
-        if (loadState is LoadState.Error) {
-            errorMsg.text = loadState.error.localizedMessage
+        binding.apply {
+
+            if (loadState is LoadState.Error) {
+                msg.text = loadState.error.localizedMessage
+            } else if (loadState.endOfPaginationReached) {
+                msg.text = binding.root.resources.getString(R.string.load_end)
+            }
+
+            progressBar.isVisible = loadState is LoadState.Loading
+            retry.isVisible = loadState is LoadState.Error
+            msg.isVisible = loadState is LoadState.Error || loadState.endOfPaginationReached
         }
 
-        progressBar.isVisible = loadState is LoadState.Loading
-        retry.isVisible = loadState is LoadState.Error
-        errorMsg.isVisible = loadState is LoadState.Error
     }
 }
diff --git a/app/src/main/res/layout/list_item_footer.xml b/app/src/main/res/layout/list_item_footer.xml
@@ -11,10 +11,11 @@
         android:orientation="vertical"
         android:padding="8dp">
 
-        <TextView
-            android:id="@+id/error_msg"
+        <com.google.android.material.textview.MaterialTextView
+            android:id="@+id/msg"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
+            android:textAppearance="?attr/textAppearanceListItem"
             android:layout_gravity="center_horizontal" />
 
         <ProgressBar
@@ -25,8 +26,8 @@
             android:indeterminateTint="?attr/colorPrimary"
             android:layout_gravity="center" />
 
-        <Button
-            android:id="@+id/retry_button"
+        <com.google.android.material.button.MaterialButton
+            android:id="@+id/retry"
             style="@style/Widget.AppCompat.Button.Colored"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"

diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
@@ -13,5 +13,6 @@
     <string name="register_fail">注册错误，请重重新输入</string>
     <string name="logout">退出登录</string>
     <string name="load_error">加载失败，请点击重试</string>
+    <string name="load_end">已加载全部内容…</string>
     <string name="no_net">请检查网络是否连接…</string>
 </resources>