DatabaseException：无法将java.lang.String类型的对象转换为type [英] DatabaseException: Can't convert object of type java.lang.String to type
问题描述
我已经看了一些其他类似问题的答案，但不明白为什么我的工作不起作用。
I've looked at a few other answers for similar problems but don't understand why mine isn't working.
我正在尝试获取我的应用程序从Firebase读取命令并移动无人机。 firebase中的命令来自一个单独的软件。该应用程序构建在Parrot Drone SDK示例代码之上。
I'm trying to get my app to read commands from Firebase and move a drone. The command in firebase comes from a separate software. The app is built on top of the Parrot Drone SDK Sample code.
它似乎能够从命令对象获取文本并将其附加到textview，但是当一个新的孩子被添加它只是崩溃。添加新子项时出现此错误。
It seems to be able to get the text from the command object and append it to a textview, but when a new child is added it just crashes. I'm getting this error when a new child is added.
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.parrot.sdksample, PID: 10592
com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.parrot.sdksample.activity.CommandObject
at com.google.android.gms.internal.zg.zzb(Unknown Source)
at com.google.android.gms.internal.zg.zza(Unknown Source)
at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
at com.parrot.sdksample.activity.MiniDroneActivity$13.onChildAdded(MiniDroneActivity.java:383)
at com.google.android.gms.internal.px.zza(Unknown Source)
at com.google.android.gms.internal.vj.zzHX(Unknown Source)
at com.google.android.gms.internal.vp.run(Unknown Source)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
我在firebase中的数据结构示例如下。
A sample of my data structure in firebase is below.
{
"drones" : {
"commands" : {
"-L-n9HwaQktOdI2VEVlH" : {
"executed" : false,
"text" : "TAKE_OFF",
"timestamp" : 1.512686825309134E9
},
"-L-nAuK5Ifde7Cdnan8K" : {
"executed" : false,
"text" : "LAND",
"timestamp" : 1.512687248764272E9
}
}
}
}
我的活动中从firebase获取数据的函数如下所示。
The function in my activity to get data from firebase looks like this.
private void initFirebase(){
mCommandTextView = (TextView) findViewById(R.id.commandTextView);
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference commandsRef = database.getReference("drones/commands");
ChildEventListener childEventListener = new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String previousChildName) {
Log.d(TAG, "onChildAdded:" + dataSnapshot.getKey());
CommandObject command = dataSnapshot.getValue(CommandObject.class);
mCommandTextView.append(command.text + "\n");
// I've tried commenting out the if statements below this, but it doesn't seem to make a difference.
if ("TAKE_OFF".equals(command.text)) {
mMiniDrone.takeOff();
} else if ("LAND".equals(command.text)) {
mMiniDrone.land();
}
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String previousChildName){
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
public void onChildMoved(DataSnapshot dataSnapshot, String previousChildName){
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
};
commandsRef.addChildEventListener(childEventListener);
}
我的CommandObject类看起来像这样。
My CommandObject class looks like this.
public class CommandObject {
public String text;
public float timestamp;
public boolean executed;
public CommandObject() {
}
public CommandObject(boolean executed, String text, float timestamp){
this.executed = executed;
this.text = text;
this.timestamp = timestamp;
}
}
我也尝试过使用值事件监听器，但同样的问题发生了。
I've also tried using a value event listener instead, but the same problem occured.
推荐答案
您收到此错误：
Can't convert object of type java.lang.String to type com.parrot.sdksample.activity.CommandObject
因为您正在尝试读取 String 类型的数据，其类型为 CommandObject 以及为什么会出现此错误。
Because you are trying to read the data of type String which is of type CommandObject and that why you are getting this error.
获取这些值的更简单方法是使用字符串这样的类：
A more simple way to get those values would be to use the String class like this:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference commandsRef = rootRef.child("drones").child("commands");
ValueEventListener eventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
boolean executed = ds.child("executed").getValue(Boolean.class);
String text = ds.child("text").getValue(String.class);
double timestamp = ds.child("timestamp").getValue(Double.class);
Log.d("TAG", executed + " / " + text + " / " + timestamp);
}
}
@Override
public void onCancelled(DatabaseError databaseError) {}
};
commandsRef.addListenerForSingleValueEvent(eventListener);
这是使用 CommandObject class：
And this the approach using an object of CommandObject class:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference commandsRef = rootRef.child("drones").child("commands");
ValueEventListener eventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
CommandObject commandObject = ds.getValue(CommandObject.class);
Log.d("TAG", commandObject.getExecuted() + " / " +
commandObject.getText() + " / " +
commandObject.getTimestamp());
}
}
@Override
public void onCancelled(DatabaseError databaseError) {}
};
commandsRef.addListenerForSingleValueEvent(eventListener);
在这两种情况下，您的输出将是：
In both cases your output will be:
false / TAKE_OFF / 1.512686825309134E9
false / LAND / 1.512687248764272E9
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