Volley 中的 JsonArrayRequest 不会将任何值传递给 ListView

Question

我正在尝试在我的项目中使用Volley，我曾经从PHP中获取JSON数组编码并将其改编为.我遵循了此页面的教程：https://www.androidhive.info/2014/07/android-custom-listview-with-image-and-text-using-volley/JsonArrayRequest()ListView我的应用程序崩溃了，下面是错误。2019-03-18 15:34:51.706 14999-14999/com.example.smartparkingapp E/AndroidRuntime: FATAL EXCEPTION: main    Process: com.example.smartparkingapp, PID: 14999    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.app.Activity.getSystemService(java.lang.String)' on a null object reference        at com.example.smartparkingapp.adapter.CarListAdapter.getView(CarListAdapter.java:48)        at android.widget.AbsListView.obtainView(AbsListView.java:3180)        at android.widget.ListView.makeAndAddView(ListView.java:2197)        at android.widget.ListView.fillDown(ListView.java:824)        at android.widget.ListView.fillFromTop(ListView.java:885)        at android.widget.ListView.layoutChildren(ListView.java:1924)        at android.widget.AbsListView.onLayout(AbsListView.java:2952)        at android.view.View.layout(View.java:21054)        at android.view.ViewGroup.layout(ViewGroup.java:6440)        at android.support.constraint.ConstraintLayout.onLayout(ConstraintLayout.java:1915)        at android.view.View.layout(View.java:21054)        at android.view.ViewGroup.layout(ViewGroup.java:6440)        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1791)        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1635)        at android.widget.LinearLayout.onLayout(LinearLayout.java:1544)        at android.view.View.layout(View.java:21054)        at android.view.ViewGroup.layout(ViewGroup.java:6440)        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)

Answer 1

您正在尝试在适配器中使用空值。将活动对象从调用活动传递到 CarListAdapter 构造函数中activity

类似的东西：在你的家庭碎片

carListAdapter = new CarListAdapter(this, carList, getActivity());

并在您的 CarListAdapter 中：

public class CarListAdapter extends BaseAdapter {

    private Activity activity;

    private Fragment fragment;

    private LayoutInflater layoutInflater;

    private List<Car> carItems;

    public CarListAdapter(Fragment fragment, List<Car> carItems, Activity activity) {

        this.fragment = fragment;

        this.carItems = carItems;

        this.activity = activity;

    }

.....

这是根据您显示的错误