java - 具有无限滚动优化的 GridView

Question

我创建了一个简单的应用程序，它从 Pixabay 获取图像，然后将它们显示在具有无限滚动功能的 GridView 中。

我的OnScrollListener:

public class BasicOnScrollListener implements AbsListView.OnScrollListener {

private IOnScroll onScroll;

public BasicOnScrollListener(IOnScroll action) {
    this.onScroll = action;
}

@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}

@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
    if (firstVisibleItem + visibleItemCount >= totalItemCount - visibleItemCount)
        onScroll.onReachedEnd();
}
}

负责数据处理的代码:

private List<Image> images = new ArrayList<>();

....

private void init() {
    this.imageAdapter = new ImageAdapter(this, images);
    this.gridView.setAdapter(imageAdapter);

    populateGridView();
    this.gridView.setOnScrollListener(new BasicOnScrollListener(() -> {
        populateGridView();
    }));
}

private void  populateGridView() {
    if (!isLoading) {
        isLoading = true;
        this.progressBar.setVisibility(View.VISIBLE);
        imagesRepository.getImages(currentPage, PAGE_SIZE, new IOnRepositoryDataReturn<ImagesList>() {
            @Override
            public void onData(ImagesList data) {
                clearIfNeeded();
                images.addAll(data.images);
                imageAdapter.notifyDataSetChanged();
                onFinish();
            }

            @Override
            public void onError(String error) {
                Toast.makeText(getApplicationContext(), error, Toast.LENGTH_LONG).show();
            }

            private void clearIfNeeded() {
                if (images.size() > 1000) {
                    images.subList(0, 300).clear();
                }
            }

            private void onFinish() {
                progressBar.setVisibility(View.INVISIBLE);
                isLoading = false;
                currentPage = currentPage + 1;
            }
        });
    }
}

一切正常，但我想对其进行优化。当 GridView 中已经有超过 1000 个项目时，我想删除前 300 个项目，这样我就不会遇到内存不足的问题。

问题是，当我简单地从列表中删除前 300 项时(如 IOnRepositoryDataReturn 实现中的 clearIfNeeded() 方法所示)，屏幕会移动。我不再看到删除前看到的项目。

示例图像。 images 列表中的第一行(第 1-2 项)被删除的情况。

• 左图 - 删除前的网格
• 居中 - 删除后的网格(就目前而言，删除顶部的项目会将所有项目向上移动)
• 正确 - 我希望它如何表现(移除某处的项目不会影响所见)

黑色方 block 代表 GridView。

我想以某种方式调整 GridView 中的查看位置，这样我仍然会看到与删除之前相同的图像。

布局 xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <ProgressBar
        android:id="@+id/ProgressSpinner"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        app:layout_constraintBottom_toBottomOf="@+id/GridView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/GridView" />

    <GridView
        android:id="@+id/GridView"
        android:layout_width="match_parent"
        android:layout_height="406dp"
        android:layout_marginBottom="8dp"
        android:numColumns="3"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

    </GridView>

Grid View 是否可行，还是我应该寻找其他可能性？

Answer 1

When there are already more than 1000 items in the GridView I'd like to remove the first 300 items, so I won't run into out of memory problems. Is it even possible with Grid View or should I look for some other possibility?

这是我的 2 美分。如果我理解正确，您的关注点似乎是防止 OutOfMemory 异常并提高内存使用率和性能。如果您使用 RecyclerView 和 GridLayoutManager 实现照片网格，它将减少许多内存问题。您尝试删除屏幕外的 300 个项目的方法似乎非常麻烦且容易出错。这是官方文档的摘录，标题为 Create a List with RecyclerView :

回收 View :

The RecyclerView uses a layout manager to position the individual items on the screen and determine when to reuse item views that are no longer visible to the user. To reuse (or recycle) a view, a layout manager may ask the adapter to replace the contents of the view with a different element from the dataset. Recycling views in this manner improves performance by avoiding the creation of unnecessary views or performing expensive findViewById() lookups.

网格布局管理器:

GridLayoutManager arranges the items in a two-dimensional grid, like the squares on a checkerboard. Using a RecyclerView with GridLayoutManager provides functionality like the older GridView layout.

您可以在快速搜索中找到许多这方面的教程，例如:Android GridLayoutManager with RecyclerView