如何处理卡片视图中不同的按钮点击和传递意图?

Question

我有一个卡片视图，它用标题、日期等显示即将发生的事件，并且有两个图像视图应该用作按钮：如果单击其中一个，它应该转到参与确认活动，如果在另一个上，则转到详细信息活动。这两者都应该使用意图(名称、日期、用户 ID、令牌(传递信息。我遵循了本教程，因为这是最接近我的问题的解决方案，但它仍然不起作用。无论我改变什么，这些都是我得到的错误：尝试在空对象引用上调用虚拟方法'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener('(这是我调用setButtons函数时给出的(，或者如果onclick以某种方式工作，意图不会传递，我得到一个空指针异常。我确保我使用了正确的ID和名称。 附加信息：我正在使用拉拉维尔和改造。活动活动：

public class EventsActivity extends AppCompatActivity {
private static final String TAG = "EventsActivity";
private static final int ACTIVITY_NUM = 1;
private static final String PREFS_NAME = "LoginPrefs";
public static final String EVENT_DETAIL = "EVENT_DETAIL";
private Context mContext = EventsActivity.this;
private Event mEvent = new Event();
private String token, name;
private int id;
private EventAdapter adapter;
private RecyclerView recyclerView;
private List<Event> eventList = new ArrayList<>();
private List<Response> result;
private TextView noEvents;
private Button add, more;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_events);
//Get token and id from shared preferences
SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
token = settings.getString("token", "");
id = settings.getInt("id", 0);
Log.d(TAG, "onResponse: id " + id + "token " + token);
noEvents = findViewById(R.id.noEvents);
recyclerView = findViewById(R.id.event_recyclerview);
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(mContext);
recyclerView.setLayoutManager(layoutManager);
adapter = new EventAdapter(mContext, eventList);
recyclerView.setAdapter(adapter);
adapter.setOnItemClickListener(new EventAdapter.OnItemClickListener() {
@Override
public void onAddClicked(int position) {
addClick(position);
}
@Override
public void onMoreClicked(int position) {
moreClick(position);
}
});
loadData();
setButtons();
}
public void addClick(int position){
final Event event = eventList.get(position);
Intent i = new Intent(EventsActivity.this, EventInvitationActivity.class);
i.putExtra("name", event.getName());
i.putExtra("name", event.getDescription());
i.putExtra("name", event.getDate());
i.putExtra("name", event.getLocation());
Log.i("hello", event.getName());
startActivity(i);
}
public void moreClick(int position){
final Event event = eventList.get(position);
Intent i = new Intent(EventsActivity.this, EventDetailActivity.class);
i.putExtra("name", event.getName());
Log.i("hello", event.getName());
startActivity(i);
}
void setButtons() {
add = findViewById(R.id.add_icon);
more = findViewById(R.id.more_icon);
Log.d(TAG, "setButtons: called");
add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.d(TAG, "onClick: add onclicklistener");
int position = Integer.parseInt(v.getTag().toString());
addClick(position);
}
});
more.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int position = Integer.parseInt(v.getTag().toString());
moreClick(position);
}
});
}
//Listing events
private void loadData(){
ApiEvents service = RetrofitBuilder.getRetrofitInstance().create(ApiEvents.class);
Call<List<Event>> call = service.listEvents("Bearer" + token, id);
call.enqueue(new Callback<List<Event>>() {
@Override
public void onResponse(@NonNull Call<List<Event>> call, @NonNull Response<List<Event>> response) {
if (response.isSuccessful() && response.body()!=null) {
Log.d(TAG, "onResponse: loadData called");
eventList = response.body();
adapter = new EventAdapter(mContext, eventList);
recyclerView.setAdapter(adapter);
adapter.setOnItemClickListener(new EventAdapter.OnItemClickListener() {
@Override
public void onAddClicked(int position) {
addClick(position);
}
@Override
public void onMoreClicked(int position) {
moreClick(position);
}
});
}
else if(response.body() == null){
noEvents.setVisibility(View.VISIBLE);
}
else{
Log.d(TAG, "onResponse: " + response.body());
}
}
@Override
public void onFailure(@NonNull Call<List<Event>> call, @NonNull Throwable t) {
Log.d("Response", "onFailure: " + t.toString());
}
});
}

}

事件适配器

public class EventAdapter extends RecyclerView.Adapter<EventAdapter.MyViewHolder> {
private Context mContext;
private List<Event> eventList;
private static final String TAG = "EventDetailActivity";
private OnItemClickListener clickListener;
public EventAdapter(Context mContext, List<Event> eventList){
this.mContext = mContext;
this.eventList = eventList;
}
public interface OnItemClickListener {
void onAddClicked(int position);
void onMoreClicked(int position);
}
public void setOnItemClickListener(OnItemClickListener clickListener) {
this.clickListener = clickListener;
}
@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.event_layout, parent, 
false);
return new MyViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull final MyViewHolder holder, int position) {
Event event = eventList.get(position);
holder.itemView.setTag(event);
holder.title.setText(eventList.get(position).getName());
holder.description.setText(eventList.get(position).getDescription());
holder.date.setText(eventList.get(position).getDate());
holder.location.setText(eventList.get(position).getLocation());
holder.add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if(clickListener != null){
int position = (int)v.getTag();
clickListener.onAddClicked(position);
final Event event = (Event)v.getTag();
if(event!= null){
Intent i = new Intent(mContext, EventInvitationActivity.class);
i.putExtra("EVENT_DETAIL", event);
v.getContext().startActivity(i);
}
}
}
});
holder.more.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if(clickListener != null){
int position = (int)v.getTag();
clickListener.onMoreClicked(position);
final Event event = (Event)v.getTag();
if(event!= null){
Intent i = new Intent(mContext, EventDetailActivity.class);
i.putExtra("EVENT_DETAIL", event);
v.getContext().startActivity(i);
}
}
}
});

@Override
public int getItemCount() {
return eventList.size();
}
public class MyViewHolder extends RecyclerView.ViewHolder {
TextView title, description, date, location;
Button add, more;
public MyViewHolder(@NonNull View itemView) {
super(itemView);
title = itemView.findViewById(R.id.event_name);
description = itemView.findViewById(R.id.event_description);
date = itemView.findViewById(R.id.event_date);
location = itemView.findViewById(R.id.event_location);
add = itemView.findViewById(R.id.add_icon);
}
}

这就是我试图在两个活动中获取传递意图的方式：

//Getting resources
mName = findViewById(R.id.eventName);
mDescription = findViewById(R.id.description);
mLocation = findViewById(R.id.location);
mDate = findViewById(R.id.date);
mEvent = Objects.requireNonNull(getIntent().getExtras()).getParcelable(EVENT_DETAIL);
if(mEvent != null){
mName.setText(mEvent.getName());
mDescription.setText(mEvent.getDescription());
mLocation.setText(mEvent.getLocation());
mDate.setText(mEvent.getDate());
}

下面是卡片视图中的按钮示例：

<Button
android:id="@+id/add_icon"
android:layout_width="80dp"
android:layout_height="40dp"
android:layout_below="@+id/image"
android:layout_gravity="center_horizontal"
android:layout_marginTop="5dp"
android:layout_toEndOf="@id/event_description"
android:drawableStart="@drawable/ic_add_black_24dp"
android:scaleType="centerCrop"
android:transitionName="img"
android:visibility="visible"
android:textColor="@color/colorAccent"
/>

所以问题是，我怎样才能做到这一点？

编辑我已经弄清楚了问题所在：添加和更多图像视图作为 CardView 的一部分在event_layout上，而不是在程序正在寻找它们的activity_events上。但是，当它们放在CardView上时，我真的不知道如何使这两个按钮工作。

Answer 1

在MyViewHolder构造函数中，您没有初始化more因此将为 null，因此会引发空引用异常

Answer 2

我假设崩溃的点击是more按钮点击侦听器，如果是，那是因为你没有初始化按钮more：

public MyViewHolder(@NonNull View itemView) {
super(itemView);
title = itemView.findViewById(R.id.event_name);
description = itemView.findViewById(R.id.event_description);
date = itemView.findViewById(R.id.event_date);
location = itemView.findViewById(R.id.event_location);
add = itemView.findViewById(R.id.add_icon);
//here you must initialize more also
more = itemView.findViewById(.......);
}

现在要传递数据并在其他活动中获取它们，我建议您传递单个数据：

holder.add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if(clickListener != null){
int position = (int)v.getTag();
clickListener.onAddClicked(position);
final Event event = (Event)v.getTag();
if(event!= null){
Intent i = new Intent(mContext, EventInvitationActivity.class);
i.putExtra("name", event.getName());
i.putExtra("date", event.getDate());
i.putExtra("description", event.getDescription());
i.putExtra("location", event.getLocation());
v.getContext().startActivity(i);
}
}
}
});

//do the same for more button

在EventInvitationActivity：

...........
//get the data
String name = getIntent().getStringExtra("name");
String date = getIntent().getStringExtra("date");
String description = getIntent().getStringExtra("description");
String location = getIntent().getStringExtra("location");
//set the data
mName.setText(name);
mDescription.setText(description);
mLocation.setText(location);
mDate.setText(date);
.........