我在Adapter和RecyclerView中设置了方法：setClickListener（），当点击项目时，它将转换到另一个活动。
我的Recycler类：
public class CategoryCarActivity extends AppCompatActivity implements AbsListView.OnScrollListener, AbsListView.OnItemClickListener, ItemClickListener {
RecyclerViewCategoryAdapter recyclerViewAdapter;
RecyclerView recyclerView;
RecyclerView.LayoutManager recyclerViewLayoutManager;
private LinearLayout linearLayoutScroll;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.recycler_category_adapter); // activity_sgv
recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
recyclerView.setHasFixedSize(true);
recyclerViewLayoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(recyclerViewLayoutManager);
// Loading tracks in Background Thread
new LoadCategoryCars().execute();
recyclerViewAdapter.setClickListener(this);
}
@Override
public void onClick(View view, int position) {
Intent i = new Intent(getApplicationContext(), DetailListCarActivityDemo1.class);
String album_id = ((TextView) view.findViewById(R.id.manufacturer_id)).getText().toString();
String price = ((TextView) view.findViewById(R.id.price)).getText().toString();
Toast.makeText(getApplicationContext(), "Car Id: " + car_id + ", Price: " + price, Toast.LENGTH_SHORT).show();
i.putExtra("car_id", car_id);
i.putExtra("price", price);
Log.i("Car ID: ", car_id);
Log.i("Price: ", price);
startActivity(i);
}
// Initialize Toolbar the first time
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.map_icon_toolbar, menu);
return true;
}
@Override
public void onScroll(final AbsListView view, final int firstVisibleItem, final int visibleItemCount, final int totalItemCount) {
Log.d(TAG, "onScroll firstVisibleItem:" + firstVisibleItem +
" visibleItemCount:" + visibleItemCount +
" totalItemCount:" + totalItemCount);
// our handling
if (!mHasRequestedMore) {
int lastInScreen = firstVisibleItem + visibleItemCount;
if (lastInScreen >= totalItemCount) {
Log.d(TAG, "onScroll lastInScreen - so load more");
mHasRequestedMore = true;
// onLoadMoreItems();
}
}
}
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
Toast.makeText(this, "Item Clicked: " + position, Toast.LENGTH_SHORT).show();
}
/**
* Background Async Task to Load all tracks under one album
* */
class LoadCategoryCars extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
protected String doInBackground(String... args) {
...
}
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(CategoryCarActivity.this);
pDialog.setMessage("Loading cars ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected void onPostExecute(String result) {
super.onPostExecute(result);
recyclerViewAdapter = new RecyclerViewCategoryAdapter(carsList, CategoryCarActivity.this);
recyclerViewAdapter.notifyDataSetChanged();
recyclerView.setAdapter(recyclerViewAdapter);
// dismiss the dialog after getting all manufacturers
if (pDialog.isShowing())
pDialog.dismiss();
}
}
}
我的适配器类：
public class RecyclerViewCategoryAdapter extends RecyclerView.Adapter<RecyclerViewCategoryAdapter.ViewHolder> {
Context context;
ArrayList<HashMap<String, String>> getCarData; // getDataAdapter
ImageLoader imageThumbLoader;
private ItemClickListener clickListener;
public RecyclerViewCategoryAdapter(ArrayList<HashMap<String, String>> getCarData, Context context){
super();
this.getCarData = getCarData;
this.context = context;
}
@Override
public RecyclerViewCategoryAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_car_info, parent, false);
RecyclerViewCategoryAdapter.ViewHolder viewHolder = new RecyclerViewCategoryAdapter.ViewHolder(v);
return viewHolder;
}
@Override
public void onBindViewHolder(RecyclerViewCategoryAdapter.ViewHolder viewholder, int position) {
HashMap<String,String> map = getCarData.get(position);
imageThumbLoader = ServerImageParseAdapter.getInstance(context).getImageLoader();
viewholder.price.setText(map.get(CategoryCarActivity.TAG_PRICE));
}
public void setClickListener(ItemClickListener itemClickListener) {
this.clickListener = itemClickListener;
}
private boolean isPositionHeader(int position) {
return position == 0;
}
class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
public NetworkImageView imageThumb;
public TextView price;
public ViewHolder(View itemView) {
super(itemView);
titleName = (TextView) itemView.findViewById(R.id.titleName);
imageThumb = (NetworkImageView) itemView.findViewById(R.id.imageThumb);
price = (TextView) itemView.findViewById(R.id.price);
itemView.setOnClickListener(this);
}
@Override
public void onClick(View view) {
if (clickListener != null) clickListener.onClick(view, getAdapterPosition());
}
}
}
我已经调试并发现构建时出现问题。
Logcat消息：
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.totoroads.android.app, PID: 3676
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.totoroads.android.app/com.totoroads.android.app.CategoryCarActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.totoroads.android.app.RecyclerViewCategoryAdapter.setClickListener(com.totoroads.android.app.ItemClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.totoroads.android.app.RecyclerViewCategoryAdapter.setClickListener(com.totoroads.android.app.ItemClickListener)' on a null object reference
at com.totoroads.android.app.CategoryCarActivity.onCreate(CategoryCarActivity.java:175)
at android.app.Activity.performCreate(Activity.java:6679)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
如何解决问题？非常感谢！
答案 0 :(得分：0)
您异步执行任务然后在onCreate中尝试访问尚未为null的recycleview适配器，因为在异步任务中执行任务，因此必须在onPostExecute中设置适配器，如下所示：
public class CategoryCarActivity extends AppCompatActivity implements AbsListView.OnScrollListener, AbsListView.OnItemClickListener, ItemClickListener {
RecyclerViewCategoryAdapter recyclerViewAdapter;
RecyclerView recyclerView;
RecyclerView.LayoutManager recyclerViewLayoutManager;
private LinearLayout linearLayoutScroll;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.recycler_category_adapter); // activity_sgv
recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
recyclerView.setHasFixedSize(true);
recyclerViewLayoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(recyclerViewLayoutManager);
// Loading tracks in Background Thread
new LoadCategoryCars().execute();
}
@Override
public void onClick(View view, int position) {
Intent i = new Intent(getApplicationContext(), DetailListCarActivityDemo1.class);
String album_id = ((TextView) view.findViewById(R.id.manufacturer_id)).getText().toString();
String price = ((TextView) view.findViewById(R.id.price)).getText().toString();
Toast.makeText(getApplicationContext(), "Car Id: " + car_id + ", Price: " + price, Toast.LENGTH_SHORT).show();
i.putExtra("car_id", car_id);
i.putExtra("price", price);
Log.i("Car ID: ", car_id);
Log.i("Price: ", price);
startActivity(i);
}
// Initialize Toolbar the first time
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.map_icon_toolbar, menu);
return true;
}
@Override
public void onScroll(final AbsListView view, final int firstVisibleItem, final int visibleItemCount, final int totalItemCount) {
Log.d(TAG, "onScroll firstVisibleItem:" + firstVisibleItem +
" visibleItemCount:" + visibleItemCount +
" totalItemCount:" + totalItemCount);
// our handling
if (!mHasRequestedMore) {
int lastInScreen = firstVisibleItem + visibleItemCount;
if (lastInScreen >= totalItemCount) {
Log.d(TAG, "onScroll lastInScreen - so load more");
mHasRequestedMore = true;
// onLoadMoreItems();
}
}
}
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
Toast.makeText(this, "Item Clicked: " + position, Toast.LENGTH_SHORT).show();
}
/**
* Background Async Task to Load all tracks under one album
* */
class LoadCategoryCars extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
protected String doInBackground(String... args) {
...
}
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(CategoryCarActivity.this);
pDialog.setMessage("Loading cars ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected void onPostExecute(String result) {
super.onPostExecute(result);
recyclerViewAdapter = new RecyclerViewCategoryAdapter(carsList, CategoryCarActivity.this);
recyclerViewAdapter.notifyDataSetChanged();
recyclerView.setAdapter(recyclerViewAdapter);
recyclerViewAdapter.setClickListener(this);
// dismiss the dialog after getting all manufacturers
if (pDialog.isShowing())
pDialog.dismiss();
}
}
}
答案 1 :(得分：0)
recyclerViewAdapter为空。你在呼叫recyclerViewAdapter.setClickListener(this);
在设置完成执行new LoadCategoryCars().execute();
删除此行recyclerViewAdapter.setClickListener(this);