Question

我正在编写一个应用程序，允许用户通过将数据上传到firebase托管的数据库来协作处理库存。我可以写数据给它没问题，但它只是想让我在触发事件时检索数据，例如数据被更改。我想要的只是检索一个我保存到数据库中的字符串，并将其设置为我页面上TextView元素的文本值，我想在单击按钮时发生这种情况。我该怎么做？

这是用户写入数据的页面的代码：

addButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            DatabaseReference mDatabase;
            mDatabase = FirebaseDatabase.getInstance().getReference();

            String dbLocationTag = location.getText().toString();
            String itemInfo = "Item Description: " + itemDescription.getText().toString() + "\n" + "Job Number: " + jobNumber.getText().toString();

            mDatabase.setValue(dbLocationTag, itemInfo);

            Context context = getApplicationContext();
            final Intent inventoryHomeScreen = new Intent();
            inventoryHomeScreen.setClass(context, Inventory_Management.class);
            startActivity(inventoryHomeScreen);
        }
    });

我希望能够检索数据：

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

    final TextView itemInfo = (TextView) findViewById(R.id.itemInfoTextView);

    final Button viewButton = (Button) findViewById(R.id.viewButton);
    assert viewButton != null;
    viewButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            //I would like to set the text of itemInfo to the data I just wrote

        }
    });
}

Answer 1

您需要使用addListenerForSingleValueEvent()来检索数据

DatabaseReference mDatabase;
mDatabase = FirebaseDatabase.getInstance().getReference();
mDatabase.child("<childName>").addListenerForSingleValueEvent(new ValueEventListener(){
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
});

在child中，您需要提及您的子节点名称

如果您想要更改整个数据库，只需删除child，使其看起来像mDatabase.addListenerForSingleValueEvent()

Answer 2

您可以使用addValueEventListener()在触发事件时检索数据。

在onClick()方法中，您可以写：

DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();

// In the database whenever any data is changed then the below code snipped is going to be executed.
mDatabase.child("<dbLocationTag>").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

                // the changed value is going to be stored into the dataSnapshot
                // to retrieve value from dataSnapshot we write

                String value = dataSnapshot.getValue(String.class);
                mValueView.setText(value);

                // NOTE: if you've multiple childs of same node then you can use Map to display all of them : EG: 
                /*Map<String, String> map = dataSnapshot.getValue(Map.class);
                String val1 = map.get("val1");
                String val2 = map.get("val2");
                String val3 = map.get("val3");
                Log.v("TAG", "Value 1 "+val1);
                Log.v("TAG", "Value 2 "+val2);
                Log.v("TAG", "Value 3 "+val3);
*/
            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {

                mValueView.setText(firebaseError.toString());

            }
        });

Answer 3

addButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        DatabaseReference mRef = mDatabaseReference.getDatabase().getReference("users");
        ValueEventListener valueEventListener = new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for (DataSnapshot ds : dataSnapshot.getChildren()) {
                    Log.d(TAG, "" + ds.getKey());
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        };
    }
});
mRef.addListenerForSingleValueEvent(valueEventListener);

以上方法对我有用。希望它对您也有帮助。

按钮点击从firebase数据库中检索数据

3 个答案: