我正在尝试构建一个应用程序，用户可以在其中发布带有图像和描述的内容，这些内容单独包含在 CardView 中的 RecyclerView 中。所以我遇到了三个问题
1.当id(userId)用作子项，然后我发布数据时，它会被旧数据替换，而不是添加新数据(如果帖子有多个具有相同ID的子项，那么我的卡片应该显示，但ID每次都会被替换时间)
NullPointerException 到方法 getDesc() 甚至生成
尽管我已经进行了空检查。之前，为了存储帖子，我使用的子项是 id(userId) ，但帖子被替换而不是添加新帖子，因此我使用了随机字符串生成器并尝试从中获取信息。
HomeFragment.java
public class HomeFragment extends Fragment {
private RecyclerView rv;
private TextView username,date,desc;
private CircleImageView postImage;
private ImageView postBigImage;
private CardView postCard;
private List<PostActivity> postItems;
private DatabaseReference dr;
private StorageReference sr;
private FirebaseUser user;
//FirebaseRecyclerAdapter<PostActivity, userViewHolder> fra;
private PostAdapter pa;
public HomeFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_home, container, false);
sr = FirebaseStorage.getInstance().getReference();
user = FirebaseAuth.getInstance().getCurrentUser();
String id = user.getUid();
AddPost ap = new AddPost();
dr =
FirebaseDatabase.getInstance().getReference().child("Posts")
.child(ap.getUni());
postItems = new ArrayList<>();
pa = new PostAdapter(postItems);
rv =view.findViewById(R.id.rvPostItems);
rv.setLayoutManager(new LinearLayoutManager(getActivity()));
rv.setAdapter(pa);
dr.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot ds : dataSnapshot.getChildren()){
//postItems.add(ds.getValue(PostActivity.class));
PostActivity pa =dataSnapshot.getValue(PostActivity.class);
postItems.add(pa);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
return view;
}
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
PostAdapter.java
package com.pappu5.navigation;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.util.List;
public class PostAdapter extends RecyclerView.Adapter<PostAdapter.ViewHolder> {
public List<PostActivity> postItems;
public PostAdapter(List<PostActivity> postItems) {
this.postItems = postItems;
}
@NonNull
@Override
public PostAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.post_items,parent,false);
return new ViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull final PostAdapter.ViewHolder holder, int position) {
String descTe = postItems.get(position).getDesc();
if(descTe!=null) {
holder.setDesc(descTe);
}else{
String def = "This is NULL";
holder.setDesc(def);
}
}
@Override
public int getItemCount() {
return postItems.size();
}
public class ViewHolder extends RecyclerView.ViewHolder{
private TextView desc;
private View mView;
public ViewHolder(View itemView) {
super(itemView);
mView = itemView;
}
public void setDesc(String descText){
desc = mView.findViewById(R.id.postDesc);
desc.setText(descText);
}
}
}
AddPost.java
package com.pappu5.navigation;
public class AddPost extends AppCompatActivity {
private Toolbar toolbar;
private ImageView postImage;
private Button postButton;
private EditText postDesc;
private static final int gallery_no = 1;
private ProgressDialog pd;
private FirebaseUser user;
private StorageReference sr;
private DatabaseReference dr;
private Uri postImageUri = null;
private Bitmap compressor;
String date = new SimpleDateFormat("yyyy-MM-dd", Locale.getDefault()).format(new Date());
protected String getSaltString() {
String SALTCHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
StringBuilder salt = new StringBuilder();
Random rnd = new Random();
while (salt.length() < 18) { // length of the random string.
int index = (int) (rnd.nextFloat() * SALTCHARS.length());
salt.append(SALTCHARS.charAt(index));
}
String saltStr = salt.toString();
return saltStr;
}
String uni = getSaltString();
public String getUni(){
return this.uni;
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add_post);
toolbar = findViewById(R.id.postBar);
setSupportActionBar(toolbar);
getSupportActionBar().setTitle("Add New Post !");
postImage = findViewById(R.id.postImage);
postDesc = findViewById(R.id.inputDesc);
postButton = findViewById(R.id.post);
sr = FirebaseStorage.getInstance().getReference();
user = FirebaseAuth.getInstance().getCurrentUser();
String id = user.getUid();
dr = FirebaseDatabase.getInstance().getReference().child("Posts").child(uni);
dr.keepSynced(true);
postImage.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent gallery = new Intent();
gallery.setType("image/*");
gallery.setAction(Intent.ACTION_GET_CONTENT);
startActivityForResult(Intent.createChooser(gallery,"Select Image"),gallery_no);
}
});
postButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String desc = postDesc.getText().toString();
if(!TextUtils.isEmpty(desc) && postImageUri!=null ){
pd = new ProgressDialog(AddPost.this);
pd.setTitle("Uploading..");
pd.setMessage("Please Wait ..");
pd.setCanceledOnTouchOutside(false);
pd.show();
final String id = user.getUid();
File thumb = new File(postImageUri.getPath());
try {
compressor = new Compressor(AddPost.this)
.setMaxWidth(200)
.setMaxHeight(200)
.setQuality(75)
.compressToBitmap(thumb);
} catch (IOException e) {
e.printStackTrace();
}
ByteArrayOutputStream baos = new ByteArrayOutputStream();
compressor.compress(Bitmap.CompressFormat.JPEG, 100, baos);
final byte[] thumb_byte = baos.toByteArray();
final StorageReference path = sr.child("Post_Images").child(id + ".jpg");
final StorageReference thumb_nail = sr.child("Post_Images").child("Thumb_Nails").child(id+".jpg");
path.putFile(postImageUri).addOnCompleteListener(new OnCompleteListener<UploadTask.TaskSnapshot>() {
@Override
public void onComplete(@NonNull Task<UploadTask.TaskSnapshot> task) {
if (task.isSuccessful()) {
path.putFile(postImageUri).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
@Override
public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
path.getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
@Override
public void onSuccess(Uri uri) {
final String down_url = uri.toString();
UploadTask uploadTask = thumb_nail.putBytes(thumb_byte);
uploadTask.addOnCompleteListener(new OnCompleteListener<UploadTask.TaskSnapshot>() {
@Override
public void onComplete(@NonNull Task<UploadTask.TaskSnapshot> task) {
thumb_nail.putFile(postImageUri).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
@Override
public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
thumb_nail.getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
@Override
public void onSuccess(Uri uri) {
final String thumb_down_url = uri.toString();
Map <String,Object> update_map = new HashMap<>();
update_map.put("image", down_url);
update_map.put("thumb_image", thumb_down_url);
update_map.put("desc",desc);
update_map.put("timestamp", date);
dr.updateChildren(update_map).addOnCompleteListener(new OnCompleteListener<Void>() {
@Override
public void onComplete(@NonNull Task<Void> task) {
if (task.isSuccessful()) {
Toast.makeText(AddPost.this, "Uploaded !", Toast.LENGTH_SHORT).show();
Intent intent = new Intent(AddPost.this,MainActivity.class);
startActivity(intent);
finish();
pd.dismiss();
} else {
Toast.makeText(AddPost.this, "Error in uploading thumbnail!", Toast.LENGTH_SHORT).show();
pd.dismiss();
}
}
});
}
});
}
});
}
});
}
});
}
});
} else {
Toast.makeText(AddPost.this, "Error!", Toast.LENGTH_SHORT).show();
pd.dismiss();
}
}
});
}
}
});
}
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == gallery_no && resultCode == RESULT_OK) {
Uri imageUri = data.getData();
CropImage.activity(imageUri).setAspectRatio(1, 1).setMinCropWindowSize(500, 500)
.start(AddPost.this);
}
if (requestCode == CropImage.CROP_IMAGE_ACTIVITY_REQUEST_CODE) {
CropImage.ActivityResult result = CropImage.getActivityResult(data);
if (resultCode == RESULT_OK) {
postImageUri = result.getUri();
postImage.setImageURI(postImageUri);
} else if (resultCode == CropImage.CROP_IMAGE_ACTIVITY_RESULT_ERROR_CODE) {
Exception error = result.getError();
}
}
}
}
post_items.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<android.support.v7.widget.CardView
android:id="@+id/postCard"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="8dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.56"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<de.hdodenhof.circleimageview.CircleImageView
android:id="@+id/postImage"
android:layout_width="65dp"
android:layout_height="65dp"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:src="@drawable/default_avatar"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/postUsername"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:text="Username"
android:textStyle="bold"
app:layout_constraintStart_toEndOf="@+id/postImage"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/postDate"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:text="Datee"
android:textStyle="italic"
app:layout_constraintStart_toEndOf="@+id/postImage"
app:layout_constraintTop_toBottomOf="@+id/postUsername" />
<ImageView
android:id="@+id/postBigImage"
android:layout_width="0dp"
android:layout_height="256dp"
android:scaleType="centerCrop"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/postImage"
tools:srcCompat="@tools:sample/avatars[3]" />
<TextView
android:id="@+id/postDesc"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:layout_marginBottom="16dp"
android:text="TextViewTextViewTextViewTextViewTextViewTextViewTextViewTextViewTextView"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/postBigImage" />
</android.support.constraint.ConstraintLayout>
</android.support.v7.widget.CardView>
</android.support.constraint.ConstraintLayout>
最佳答案
要修复 NullPointerException，请检查 postItems.get(position) 的 null 值，而不是 postItems.get(position).getDesc() ，即
@Override
public void onBindViewHolder(@NonNull final PostAdapter.ViewHolder holder, int position) {
if(postItems.get(position) != null) {
String descTe = postItems.get(position).getDesc();
holder.setDesc(descTe);
} else {
String def = "This is NULL";
holder.setDesc(def);
}
}
此外，您正在使用空白的 postItems 列表初始化 PostAdapter，即
postItems = new ArrayList<>();
pa = new PostAdapter(postItems);
项目随后添加到 ValueEventListener 的 onDataChange() 方法中。您必须为新更新的 List postItems 更新 PostAdapter 并通知适配器。像这样。
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot ds : dataSnapshot.getChildren()){
//postItems.add(ds.getValue(PostActivity.class));
PostActivity pa =dataSnapshot.getValue(PostActivity.class);
postItems.add(pa);
}
pa.notifyDataSetChanged();
}
对于未显示的卡片，您可以分享 post_items.xml 文件的代码吗？
关于java - Android Firebase - 卡未在 RecyclerView 和 NullPointerException 中显示，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/56680332/