Question

我正在开发一款应用。我想列出朋友片段中的项目，当我点击该项目然后转到消息片段（另一个片段）。我的代码如下。

FriendsFragment.java

public class FriendsFragment extends android.support.v4.app.Fragment {

CardView cardView;
List<GetDataAdapter> GetDataAdapter1;
RecyclerView recyclerView;
RecyclerView.LayoutManager recyclerViewlayoutManager;
RecyclerView.Adapter recyclerViewadapter;

String GET_JSON_DATA_HTTP_URL = "http://192.168.43.7/work/ecom/2/1.php";
String JSON_IMAGE_TITLE_NAME = "image_title";
String JSON_IMAGE_URL = "image_url";

JsonArrayRequest jsonArrayRequest ;
RequestQueue requestQueue ;
public FriendsFragment() {
    // Required empty public constructor
}
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);


}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_friends, container, false);
    GetDataAdapter1 = new ArrayList<>();
    recyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerview1);
    recyclerView.setHasFixedSize(true);
    recyclerViewlayoutManager = new LinearLayoutManager(getContext());
    recyclerView.setLayoutManager(recyclerViewlayoutManager);



    cardView = (CardView) rootView.findViewById(R.id.cardview1);


    cardView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Log.d("LOGTAG", "clicked");
            MessagesFragment fragment = new MessagesFragment();
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction().replace(R.id.container_body, fragment).commit();


        }
    });


    JSON_DATA_WEB_CALL();



    // Inflate the layout for this fragment
    return rootView;
}

public void JSON_DATA_WEB_CALL(){

    jsonArrayRequest = new JsonArrayRequest(GET_JSON_DATA_HTTP_URL,

            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response) {

                    Log.d("LOGTAG", "Response :"+response);

                    JSON_PARSE_DATA_AFTER_WEBCALL(response);
                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {

                }
            });

    requestQueue = Volley.newRequestQueue(getContext());

    requestQueue.add(jsonArrayRequest);
}


public void JSON_PARSE_DATA_AFTER_WEBCALL(JSONArray array){

    for(int i = 0; i<array.length(); i++) {

        GetDataAdapter GetDataAdapter2 = new GetDataAdapter();

        JSONObject json = null;
        try {

            json = array.getJSONObject(i);

            GetDataAdapter2.setImageTitleNamee(json.getString(JSON_IMAGE_TITLE_NAME));

            GetDataAdapter2.setImageServerUrl(json.getString(JSON_IMAGE_URL));

        } catch (JSONException e) {

            e.printStackTrace();
        }
        GetDataAdapter1.add(GetDataAdapter2);
    }

    recyclerViewadapter = new RecyclerViewAdapter(GetDataAdapter1, getContext());

    recyclerView.setAdapter(recyclerViewadapter);

}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
}

@Override
public void onDetach() {
    super.onDetach();
}
}

当我添加

  cardView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Log.d("LOGTAG", "clicked");
           /* MessagesFragment fragment = new MessagesFragment();
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction().replace(R.id.container_body, fragment).commit();*/


        }
    });

显示错误

FATAL EXCEPTION: main
                                                                Process: com.ecom.fragment2, PID: 21541
                                                                java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.CardView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                    at com.ecom.fragment2.FriendsFragment.onCreateView(FriendsFragment.java:77)
                                                                    at android.support.v4.app.Fragment.performCreateView(Fragment.java:2080)
                                                                    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1108)
                                                                    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1290)
                                                                    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801)
                                                                    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1677)
                                                                    at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:536)
                                                                    at android.os.Handler.handleCallback(Handler.java:739)
                                                                    at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                    at android.os.Looper.loop(Looper.java:135)
                                                                    at android.app.ActivityThread.main(ActivityThread.java:5312)
                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                    at java.lang.reflect.Method.invoke(Method.java:372)
                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)

fragment_friends.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.ecom.fragment2.FriendsFragment">

<android.support.v7.widget.RecyclerView
    android:id="@+id/recyclerview1"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" />

</RelativeLayout>

recyclerview_items.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:id="@+id/cardview1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
card_view:cardElevation="3dp"
card_view:contentPadding="3dp"
card_view:cardCornerRadius="3dp"
card_view:cardMaxElevation="3dp"
>


<RelativeLayout
    android:layout_width="fill_parent"
    android:layout_height="wrap_content">

    <com.android.volley.toolbox.NetworkImageView
        android:id="@+id/VollyNetworkImageView1"
        android:layout_width="150dp"
        android:layout_height="100dp"
        android:src="@mipmap/ic_launcher"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Image Name"
        android:id="@+id/textView_item"
        android:layout_centerVertical="true"
        android:layout_toRightOf="@+id/VollyNetworkImageView1"
        android:layout_toEndOf="@+id/VollyNetworkImageView1"
        android:layout_marginLeft="20dp"/>

</RelativeLayout>

</android.support.v7.widget.CardView>

请帮帮我

Answer 1

问题来自

cardView = (CardView) rootView.findViewById(R.id.cardview1);

线。

因为带有CardView id的R.id.cardview1位于RecyclerView的行布局内，但使用rootView.findViewById尝试从错误的布局fragment_friends访问它。

要解决此问题，请在setOnClickListener类

的onBindViewHolder方法内向CardView添加RecyclerViewAdapter

Answer 2

问题在ρяσѕρєяK的答案中有所解释，但我想补充一点。

对我来说，一个好习惯是创建自定义视图类，这样就可以在构造函数中设置所需的所有侦听器。

然后在您的RecyclerView适配器中，您可以覆盖此方法，如下所示：

@Override public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View v = new MyCustomView();
    return new ViewHolder(v);
}

您的侦听器在MyCustomView实例化期间设置，您可以使用事件方式将事件传递给您的片段。有很多图书馆在做这项工作，一个很好的例子是Otto

Answer 3

我的回答。

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> {

Context context;

List<GetDataAdapter> getDataAdapter;

ImageLoader imageLoader1;

private final View.OnClickListener mOnClickListener = new MyOnClickListener();


public RecyclerViewAdapter(List<GetDataAdapter> getDataAdapter, Context context){

    super();
    this.getDataAdapter = getDataAdapter;
    this.context = context;
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

    View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.recyclerview_items, parent, false);
    v.setOnClickListener(mOnClickListener);
    ViewHolder viewHolder = new ViewHolder(v);

        return viewHolder;
}
@Override
public void onBindViewHolder(ViewHolder Viewholder, int position) {

    GetDataAdapter getDataAdapter1 =  getDataAdapter.get(position);

    Viewholder.ImageTitleNameView.setText(getDataAdapter1.getImageTitleName());

    imageLoader1 = ServerImageParseAdapter.getInstance(context).getImageLoader();

    imageLoader1.get(getDataAdapter1.getImageServerUrl(),
            ImageLoader.getImageListener(
                    Viewholder.networkImageView,//Server Image
                    R.mipmap.ic_launcher,//Before loading server image the default showing image.
                    android.R.drawable.ic_dialog_alert //Error image if requested image dose not found on server.
            )
    );

    Viewholder.networkImageView.setImageUrl(getDataAdapter1.getImageServerUrl(), imageLoader1);

    Viewholder.ImageTitleNameView.setText(getDataAdapter1.getImageTitleName());

}

@Override
public int getItemCount() {

    return getDataAdapter.size();
}

class ViewHolder extends RecyclerView.ViewHolder{



    public TextView ImageTitleNameView;
    public NetworkImageView networkImageView ;

    public ViewHolder(View itemView) {

        super(itemView);

        ImageTitleNameView = (TextView) itemView.findViewById(R.id.textView_item) ;

        networkImageView = (NetworkImageView) itemView.findViewById(R.id.VollyNetworkImageView1) ;

    }
}

private class MyOnClickListener implements View.OnClickListener {

    @Override
    public void onClick(View v) {


        //Log.d("LOGTAG", "clicked");

    }
}
}

无法移动到recycleview中的另一个片段

3 个答案: