Android 如何检索数据?Firebase 3.0数据库
例如,如何从“Compressor_1”中检索所有child Firebase数据库:Android 如何检索数据?Firebase 3.0数据库,android,firebase,firebase-realtime-database,Android,Firebase,Firebase Realtime Database,例如,如何从“Compressor_1”中检索所有child Firebase数据库: "CompresoresEstandar" : { "Compresor_1" : { "Marca" : "SANDEN", "Modelo" : "505/5H09", "Canales" : "PV5",
"CompresoresEstandar" : {
"Compresor_1" : {
"Marca" : "SANDEN",
"Modelo" : "505/5H09",
"Canales" : "PV5",
"Dimametro-MM" : "120",
"Voltios" : "12",
"Conexion" : "V-O",
},
"Compresor_2" : {
"Marca" : "SANDEN",
"Modelo" : "505/5H09",
"Canales" : "PV5",
"Dimametro-MM" : "120",
"Voltios" : "12",
"Conexion" : "V-O",
},
从网络上尝试了此示例,但它显示了以下错误:
com.google.firebase.database.DatabaseException: Class java.util.Map has generic type parameters, please use GenericTypeIndicator instead
更新1
已经尝试了以下内容:
GenericTypeIndicator<Map<String, String>> genericTypeIndicator = new GenericTypeIndicator<Map<String, String>>() {};
Map<String, String> map = dataSnapshot.getValue(genericTypeIndicator );
工作代码
@Override
public void onStart(){
super.onStart();
final FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference compresoresRef = database.getReference("CompresoresEstandar");
compresoresRef.orderByChild("Ref").addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
dataSnapshot.getChildren();
CompresorModel coe = dataSnapshot.getValue(CompresorModel.class);
String modelo = coe.getModelo();
String marca = coe.getMarca();
String canales = coe.getCanales();
textData1.setText(modelo);
textData2.setText(marca);
textData3.setText(canales);
}
如果每个节点都包含与我从JSON文件中看到的相同的子节点,则可以为compressores对象创建一个模型类 在这里:
压缩标准单元类
public class CompresoresEstandarUnit {
String Marca;
String Modelo;
String Canales;
String Dimametro_MM; //Recommend you to change Firebase Node name to Dimametro_MM
String Voltios;
String Conextion;
public CompresoresEstandarUnit() {
//Firebase Empty Constructor
}
public String getCanales() {
return Canales;
}
public void setCanales(String canales) {
Canales = canales;
}
public String getConextion() {
return Conextion;
}
public void setConextion(String conextion) {
Conextion = conextion;
}
public String getDimametro_MM() {
return Dimametro_MM;
}
public void setDimametro_MM(String dimametro_MM) {
Dimametro_MM = dimametro_MM;
}
public String getMarca() {
return Marca;
}
public void setMarca(String marca) {
Marca = marca;
}
public String getModelo() {
return Modelo;
}
public void setModelo(String modelo) {
Modelo = modelo;
}
public String getVoltios() {
return Voltios;
}
public void setVoltios(String voltios) {
Voltios = voltios;
}
}
然后在你的听众中:
@Override
public void onStart(){
super.onStart();
DatabaseReference mRootRef = FirebaseDatabase.getInstance().getReference();
mRootRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
dataSnapshot.getChildren();
CompresoresEstandarUnit coe = dataSnapshot.getValue(CompresoresEstandarUnit.class);
String modelo = coe.getModelo();
mConditionTextView.setText(modelo);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});*/
这种面向对象的方法将为结构提供灵活性。可能重复以前尝试过的解决方案,但没有解决它。显示您使用
GenericTypeIndicator尝试过的内容。
。欢迎使用任何示例,谢谢。出现错误,但大写似乎没有问题。我抄了你的并修改了它。致命异常com.google.firebase.database.DatabaseException:发现两个getter或字段的属性区分大小写冲突:canalesPlease请参阅:@Frank已在此处进行了深入解释。此外,您是否更改了Dimametro MM节点?请看,就序列化实践而言,使用与节点名称完全相同的变量是最好的方法。由于Java不支持-
,我建议您也使用可以序列化为变量的内容更改节点密钥。出现此错误(类似于更新1):无法将Java.lang.String类型的对象转换为compressorModel类型。请更新一次代码好吗?我怀疑你读的是子值而不是compressor的节点。。。
public class CompresoresEstandarUnit {
String Marca;
String Modelo;
String Canales;
String Dimametro_MM; //Recommend you to change Firebase Node name to Dimametro_MM
String Voltios;
String Conextion;
public CompresoresEstandarUnit() {
//Firebase Empty Constructor
}
public String getCanales() {
return Canales;
}
public void setCanales(String canales) {
Canales = canales;
}
public String getConextion() {
return Conextion;
}
public void setConextion(String conextion) {
Conextion = conextion;
}
public String getDimametro_MM() {
return Dimametro_MM;
}
public void setDimametro_MM(String dimametro_MM) {
Dimametro_MM = dimametro_MM;
}
public String getMarca() {
return Marca;
}
public void setMarca(String marca) {
Marca = marca;
}
public String getModelo() {
return Modelo;
}
public void setModelo(String modelo) {
Modelo = modelo;
}
public String getVoltios() {
return Voltios;
}
public void setVoltios(String voltios) {
Voltios = voltios;
}
}
@Override
public void onStart(){
super.onStart();
DatabaseReference mRootRef = FirebaseDatabase.getInstance().getReference();
mRootRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
dataSnapshot.getChildren();
CompresoresEstandarUnit coe = dataSnapshot.getValue(CompresoresEstandarUnit.class);
String modelo = coe.getModelo();
mConditionTextView.setText(modelo);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});*/