Android RecyclerView适配器在单元测试时给出null [英] Android RecyclerView Adapter is giving null on unit testing

问题描述

我正在尝试使用AndroidJunit4测试RecyclerView，这是我的测试代码：

I am trying to test RecyclerView with AndroidJunit4, it is my test code:

package com.kaushik.myredmart.ui;
// all includes
@RunWith(AndroidJUnit4.class)
public class ProductListActivityTest {

    @Rule
    public ActivityTestRule<ProductListActivity> rule  = new  ActivityTestRule<>(ProductListActivity.class);

    @Test
    public void ensureListViewIsPresent() throws Exception {
        ProductListActivity activity = rule.getActivity();
        View viewByIdw = activity.findViewById(R.id.productListView);
        assertThat(viewByIdw,notNullValue());
        assertThat(viewByIdw, instanceOf(RecyclerView.class));
        RecyclerView productRecyclerView = (RecyclerView) viewByIdw;
        RecyclerView.Adapter adapter = productRecyclerView.getAdapter();
        assertThat(adapter, instanceOf(ProductAdapter.class));

    }
}

我正面临检查问题适配器。虽然productRecyclerView传递非空测试和RecyclerView实例，但它在最后一行中跟随错误：

I am facing a problem to check the Adapter. Although productRecyclerView is passing not null test and an instance of RecyclerView, it is following error in last line:

java.lang.AssertionError:
Expected: an instance of com.kaushik.myredmart.adapter.ProductAdapter
but: null
at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
at org.junit.Assert.assertThat(Assert.java:956)
at org.junit.Assert.assertThat(Assert.java:923)
at com.kaushik.myredmart.ui.ProductListActivityTest.ensureListViewIsPresent(ProductListActivityTest.java:45)

代码中有什么问题？

推荐答案

从这一行判断：

预期：com的一个实例.kaushik.myredmart.adapter.ProductAdapter
但是：null

Expected: an instance of com.kaushik.myredmart.adapter.ProductAdapter but: null

可以得出结论：

RecyclerView.Adapter adapter = productRecyclerView.getAdapter();

返回 null ，这可能发生在那里尚未执行 productRecyclerView.setAdapter（适配器）。

returns null, which may happen when there has not been performed productRecyclerView.setAdapter(adapter).

确保在活动生命周期回调中正确设置适配器（即在 onCreate（））。在我看来，你是在一些动作/回调后创建和设置适配器。

Make sure you are correctly setting adapter in activity lifecycle callbacks (i.e. in onCreate()). It seems to me you are creating and setting adapter after some action/callback.

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