如何在 Android Studio 中从 Firebase 实时数据库中的 URL 检索图像

Question

我正在尝试提取名为“imageUrl”的 URL，以便从 Firebase 实时数据库的 URL 中检索图像，如下所示：

这是 Firebase 实时数据库中的数据库结构：

enter image description here

我有这个数据库：

{
  "Image": {
    "01": {
      "id": "1",
      "name": "img1",
      "imageUrl": "https://www.pexels.com/photo/beach-calm-clouds-coast-457881/"
    },
    "02": {
      "id": "2",
      "name": "img2",
      "imageUrl": "https://www.pexels.com/photo/sea-beach-holiday-vacation-42151/"
    }
  }
}

这是 Android Studio 中的一个 Activity：

    public class BigToePose extends AppCompatActivity {

    private Context context;
    private ImageView img;

    private FirebaseDatabase database;
    private DatabaseReference mReference;
    private DatabaseReference childReference;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.bigtoepose);

        context = this;
        img = findViewById(R.id.imageView);

        database = FirebaseDatabase.getInstance();
        mReference = database.getReference();
        childReference = mReference.child("Image").child("01");
    }

    @Override
    protected void onStart() {
        super.onStart();
        childReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                String url = dataSnapshot.child("imageUrl").getValue(String.class);
                Picasso.with(context)
                        .load(url)
                        .into(img);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }
}

我尝试将此代码作为要从 Android Studio 中的另一个 Activity 移动到的 Activity 执行，但看起来该 Activity 没有显示。我怎样才能让它工作？

Answer 1

由于您试图在执行的方法之外获取 firebase 引用，因此它可能根本不会被执行。 尝试通过更改代码如下：-

public class BigToePose extends AppCompatActivity {

private Context context;
private TextView url;
private ImageView img;

private FirebaseDatabase database ;
private DatabaseReference mReference ;
private DatabaseReference childReference ;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.bigtoepose);

    context = this;
    img = findViewById(R.id.imageView);

   // place here
   database = FirebaseDatabase.getInstance();
   mReference = database.getReference("Image");
   childReference = mReference.child("01");
 }

@Override
protected void onStart() {
    super.onStart();
    childReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            String message = dataSnapshot.child("imageUrl").getValue(String.class);
            Picasso.with(context)
                    .load(message)
                    .into(img);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
      });
  }
}

Answer 2

我有类似的问题，我正在分享我的例子。看看它是如何为我工作的。

{"Questions": {
"1": {
  "question": "One MB is equal to",
  "option1": "1024KB",
  "option2": "1024Byte",
  "option3": "1000KB",
  "option4": "1024GB",
  "answer": "1024KB",
  "hint": "https://www.pexels.com/photo/123-let-s-go-imaginary-text-704767/"
},
"2": {
  "question": "What s used to make computer chips",
  "option1": "copper",
  "option2": "steel",
  "option3": "silicon",
  "option4": "iron",
  "answer": "silicon",
  "hint": "https://www.pexels.com/photo/grayscale-photography-of-railroad-crossing-signage-981294/"
}}}

看看这是我在 Android Studio 中的代码。但是我的图像存储在 firebase 存储中，而您的图像存储在像素上。那是有区别的。

public class Hint extends MainActivity {

private TextView url;
private ImageView img;
DatabaseReference childReference;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_hint);

    url = findViewById(R.id.mURLText);
    img = findViewById(R.id.mHintImage);

    childReference = FirebaseDatabase.getInstance().getReference().child("Questions").child("1").child("Hint");
}

@Override
protected void onStart() {
    super.onStart();
    childReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            String message = snapshot.getValue(String.class);
            url.setText(message);
            Picasso.get()
                    .load(message)
                    .into(img);
        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {

        }
    });
}}

所以在你的情况下你的代码应该是这样的：

public class BigToePose extends AppCompatActivity {

private Context context;
private ImageView img;

private FirebaseDatabase database;
private DatabaseReference mReference;
private DatabaseReference childReference;
private Int url; // for a new TextView you'll have to create which I've mentioned below

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.bigtoepose);

    context = this;
    url = findViewById(R.Id.mURLText); // you will have to add a textView in your XML file and initiate it here, like I did here
    img = findViewById(R.id.imageView);

    database = FirebaseDatabase.getInstance();
    mReference = database.getReference();
    childReference = mReference.child("Image").child("01").child(imageUrl);
}

@Override
protected void onStart() {
    super.onStart();
    childReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            String message = dataSnapshot.getValue(String.class);
            url.setText(message);
            Picasso.get()
                    .load(message)
                    .into(img);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
  }
}

希望对你有帮助。