Use our own homemade paging library for conversation paging.

I made the lib, and Alan made the build actually work.

Co-authored-by: Alan Evans <alan@signal.org>

paging/app/src/main/java/org/signal/pagingtest/MainActivity.java

@@ -0,0 +1,135 @@
+package org.signal.pagingtest;
+
+import androidx.annotation.NonNull;
+import androidx.appcompat.app.AppCompatActivity;
+import androidx.lifecycle.ViewModelProvider;
+import androidx.recyclerview.widget.LinearLayoutManager;
+import androidx.recyclerview.widget.RecyclerView;
+
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.TextView;
+
+import org.signal.paging.PagingController;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class MainActivity extends AppCompatActivity {
+
+  @Override
+  protected void onCreate(Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+    setContentView(R.layout.activity_main);
+
+    MyAdapter           adapter       = new MyAdapter();
+    RecyclerView        list          = findViewById(R.id.list);
+    LinearLayoutManager layoutManager = new LinearLayoutManager(this);
+
+    list.setAdapter(adapter);
+    list.setLayoutManager(layoutManager);
+
+    MainViewModel viewModel = new ViewModelProvider(this, new ViewModelProvider.NewInstanceFactory()).get(MainViewModel.class);
+    adapter.setPagingController(viewModel.getPagingController());
+    viewModel.getList().observe(this, newList -> {
+      adapter.submitList(newList);
+    });
+
+    findViewById(R.id.invalidate_btn).setOnClickListener(v -> {
+      viewModel.getPagingController().onDataInvalidated();
+    });
+
+    findViewById(R.id.down250_btn).setOnClickListener(v -> {
+      int target = Math.min(adapter.getItemCount() - 1, layoutManager.findFirstVisibleItemPosition() + 250);
+      layoutManager.scrollToPosition(target);
+    });
+
+    findViewById(R.id.up250_btn).setOnClickListener(v -> {
+      int target = Math.max(0, layoutManager.findFirstVisibleItemPosition() - 250);
+      layoutManager.scrollToPosition(target);
+    });
+
+    findViewById(R.id.append_btn).setOnClickListener(v -> {
+      viewModel.appendItems();
+    });
+  }
+
+  static class MyAdapter extends RecyclerView.Adapter<MyViewHolder> {
+
+    private final static int TYPE_NORMAL      = 1;
+    private final static int TYPE_PLACEHOLDER = -1;
+
+    private PagingController controller;
+
+    private final List<String> data = new ArrayList<>();
+
+    public MyAdapter() {
+      setHasStableIds(true);
+    }
+
+    @Override
+    public int getItemViewType(int position) {
+      return getItem(position) == null ? TYPE_PLACEHOLDER : TYPE_NORMAL;
+    }
+
+    @Override
+    public int getItemCount() {
+      return data.size();
+    }
+
+    @Override
+    public long getItemId(int position) {
+      return position;
+    }
+
+    @Override
+    public @NonNull MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
+      switch (viewType) {
+        case TYPE_NORMAL:
+          return new MyViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false));
+        case TYPE_PLACEHOLDER:
+          return new MyViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false));
+        default:
+          throw new AssertionError();
+      }
+    }
+
+    @Override
+    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
+      holder.bind(getItem(position));
+    }
+
+    private String getItem(int index) {
+      if (controller != null) {
+        controller.onDataNeededAroundIndex(index);
+      }
+      return data.get(index);
+    }
+
+    void setPagingController(PagingController pagingController) {
+      this.controller = pagingController;
+    }
+
+    void submitList(List<String> list) {
+      data.clear();
+      data.addAll(list);
+      notifyDataSetChanged();
+    }
+  }
+
+  static class MyViewHolder extends RecyclerView.ViewHolder {
+
+    TextView textView;
+
+    public MyViewHolder(@NonNull View itemView) {
+      super(itemView);
+      textView = itemView.findViewById(R.id.text);
+    }
+
+    void bind(@NonNull String s) {
+      textView.setText(s == null ? "PLACEHOLDER" : s);
+    }
+  }
+}

paging/app/src/main/java/org/signal/pagingtest/MainViewModel.java

@@ -0,0 +1,74 @@
+package org.signal.pagingtest;
+
+import androidx.annotation.NonNull;
+import androidx.lifecycle.LiveData;
+import androidx.lifecycle.ViewModel;
+
+import org.signal.paging.PagedDataSource;
+import org.signal.paging.PagingController;
+import org.signal.paging.PagingConfig;
+import org.signal.paging.PagedData;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class MainViewModel extends ViewModel {
+
+  private final PagedData<String> pagedData;
+  private final MyDataSource      dataSource;
+
+  public MainViewModel() {
+    this.dataSource = new MyDataSource(1000);
+    this.pagedData = PagedData.create(dataSource, new PagingConfig.Builder().setBufferPages(3)
+                                                                            .setPageSize(25)
+                                                                            .build());
+  }
+
+  public @NonNull LiveData<List<String>> getList() {
+    return pagedData.getData();
+  }
+
+  public @NonNull PagingController getPagingController() {
+    return pagedData.getController();
+  }
+
+  public void appendItems() {
+    dataSource.setSize(dataSource.size() + 1);
+    pagedData.getController().onDataInvalidated();
+  }
+
+  private static class MyDataSource implements PagedDataSource<String> {
+
+    private int size;
+
+    MyDataSource(int size) {
+      this.size = size;
+    }
+
+    public void setSize(int size) {
+      this.size = size;
+    }
+
+    @Override
+    public int size() {
+      return size;
+    }
+
+    @Override
+    public List<String> load(int start, int length, @NonNull CancellationSignal cancellationSignal) {
+      try {
+        Thread.sleep(500);
+      } catch (InterruptedException e) {
+        e.printStackTrace();
+      }
+
+      List<String> data = new ArrayList<>(length);
+
+      for (int i = 0; i < length; i++) {
+        data.add(String.valueOf(start + i) + "     (" + System.currentTimeMillis() + ")");
+      }
+
+      return data;
+    }
+  }
+}