Android开源项目PullToRefresh下拉刷新功能详解

PullToRefresh简介

PullToRefresh是一款在Android平台上使用的可拓展、易定制下拉刷新控件，现在已经迁移至AndroidX。PullToRefresh支持下拉刷新和上拉加载更多功能，非常适用于数据列表的情况。

导入PullToRefresh库

PullToRefresh库可以通过Gradle进行引入，将以下代码添加到项目的build.gradle文件中：

dependencies {
    implementation 'com.scwang.smart:refresh-layout-kernel:2.0.3'
    //如果要使用默认的下拉刷新样式，还需要引入：
    implementation 'com.scwang.smart:refresh-header-classics:2.0.3'
}

布局文件使用示例

在app的布局文件中添加以下代码：

<com.scwang.smartrefresh.layout.SmartRefreshLayout
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/refreshLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:srlEnableLoadMore="false"
    app:srlEnablePureScrollMode="false"
    app:srlDisableContentWhenRefresh="true"
    app:srlDisableContentWhenLoading="true">
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</com.scwang.smartrefresh.layout.SmartRefreshLayout>

以上布局代码包含一个SmartRefreshLayout和一个RecyclerView。其中，srlEnableLoadMore表示是否启用上拉加载更多功能，srlEnablePureScrollMode表示是否开启纯滚动模式，srlDisableContentWhenRefresh表示在刷新时是否禁止操作其他内容，srlDisableContentWhenLoading表示在加载时是否禁止操作其他内容。

代码实现示例

以下是拉取数据时使用SmartRefreshLayout的示例代码：

public class MainActivity extends AppCompatActivity implements OnRefreshListener {
    private SmartRefreshLayout refreshLayout;
    private RecyclerView recyclerView;
    private RecyclerViewAdapter recyclerViewAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        refreshLayout = findViewById(R.id.refreshLayout);
        refreshLayout.setOnRefreshListener(this);
        recyclerView = findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerViewAdapter = new RecyclerViewAdapter(this, getData());
        recyclerView.setAdapter(recyclerViewAdapter);
    }

    private List<String> getData() {
        List<String> dataList = new ArrayList<>();
        for (int i = 0; i < 20; i++) {
            dataList.add("item" + i);
        }
        return dataList;
    }

    @Override
    public void onRefresh(@NonNull RefreshLayout refreshLayout) {
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                List<String> dataList = new ArrayList<>();
                for (int i = 0; i < 20; i++) {
                    dataList.add("new item" + i);
                }
                recyclerViewAdapter.setData(dataList);
                refreshLayout.finishRefresh();
            }
        }, 2000);
    }
}

该示例中，onCreate方法中初始化了SmartRefreshLayout和RecyclerView，并通过RecyclerViewAdapter显示数据，getData方法获取数据，onRefresh方法表示当PullToRefresh被触发时，将刷新数据并调用finishRefresh方法结束刷新。

另一示例

以下是通过代码使用SmartRefreshLayout设置自定义Header和Footer的示例代码：

public class MainActivity extends AppCompatActivity implements OnRefreshLoadMoreListener {
    private SmartRefreshLayout refreshLayout;
    private RecyclerView recyclerView;
    private RecyclerViewAdapter recyclerViewAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        refreshLayout = findViewById(R.id.refreshLayout);
        refreshLayout.setOnRefreshLoadMoreListener(this);
        refreshLayout.setRefreshHeader(new ClassicsHeader(this));
        refreshLayout.setRefreshFooter(new ClassicsFooter(this));
        recyclerView = findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerViewAdapter = new RecyclerViewAdapter(this, getData());
        recyclerView.setAdapter(recyclerViewAdapter);
    }

    private List<String> getData() {
        List<String> dataList = new ArrayList<>();
        for (int i = 0; i < 20; i++) {
            dataList.add("item" + i);
        }
        return dataList;
    }

    @Override
    public void onLoadMore(@NonNull RefreshLayout refreshLayout) {
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                int size = recyclerViewAdapter.getItemCount();
                List<String> dataList = new ArrayList<>();
                for (int i = size; i < size + 20; i++) {
                    dataList.add("new item" + i);
                }
                recyclerViewAdapter.addMoreData(dataList);
                refreshLayout.finishLoadMore();
            }
        }, 2000);
    }

    @Override
    public void onRefresh(@NonNull RefreshLayout refreshLayout) {
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                List<String> dataList = new ArrayList<>();
                for (int i = 0; i < 20; i++) {
                    dataList.add("new item" + i);
                }
                recyclerViewAdapter.setData(dataList);
                refreshLayout.finishRefresh();
            }
        }, 2000);
    }
}

该示例中，onCreate方法中使用refreshLayout.setRefreshHeader设置自定义下拉刷新头部，使用refreshLayout.setRefreshFooter设置自定义上拉加载更多尾部，onLoadMore方法表示当pull-to-loading被触发时，将新增数据并调用finishLoadMore方法结束加载更多。