DataSnapshot.getValue 无法解析类型 T答案

【问题标题】：DataSnapshot.getValue Could not resolve type TDataSnapshot.getValue 无法解析类型 T
【发布时间】：2016-09-24 04:32:55
【问题描述】：

这是我扩展 ScoutMetric<ArrayList<String>> 的微调器类：

public class ScoutSpinner extends ScoutMetric<ArrayList<String>> {
    private int mSelectedValue;

    public ScoutSpinner() {
    }

    public ScoutSpinner(String name, ArrayList<String> values, int selectedValue) {
        super(name, values);
        mSelectedValue = selectedValue;
    }

    public int getSelectedValue() {
        return mSelectedValue;
    }

    public void setSelectedValue(int selectedValue) {
        mSelectedValue = selectedValue;
    }

    public void setSelectedValue(DatabaseReference databaseReference, int selectedValue) {
        databaseReference.child("selectedValue").setValue(selectedValue);
        mSelectedValue = selectedValue;
    }
}

这是我的 ScoutMetric 课程：

public class ScoutMetric<T> {
    private String mName;
    private T mValue;
    private int mType;

    public ScoutMetric() {
    }

    public ScoutMetric(String name, T value) {
        setName(name);
        mValue = value;
    }

    public String getName() {
        return mName;
    }

    public void setName(String name) {
        mName = name;
    }

    public T getValue() {
        return mValue;
    }

    public void setValue(T value) {
        mValue = value;
    }

    public void setValue(DatabaseReference databaseReference, T value) {
        databaseReference.child(Constants.FIREBASE_VALUE).setValue(value);
        mValue = value;
    }

    public int getType() {
        return mType;
    }

    public void setType(Integer type) {
        mType = type;
    }

    public ScoutMetric<T> setType(int type) {
        mType = type;
        return this;
    }
}

我正在尝试获取这样的值：

return snapshot.getValue(new GenericTypeIndicator<ScoutSpinner>() {});

它应该可以工作，因为我明确地创建了 ArrayList 类型：ScoutMetric<ArrayList<String>>

我做错了什么？或者这是 Firebase 中的错误？（顺便说一句，使用 v9.6.0）

PS：这是我为了规避这个问题而处理的那种恶心（不好玩）：

new ScoutSpinner(
  snapshot.child("name").getValue(String.class),
  snapshot.child("value").getValue(new GenericTypeIndicator<ArrayList<String>>() {}),
  snapshot.child("selectedValue").getValue(Integer.class)
).setType(Constants.SPINNER);

这是我的完整例外：

09-23 21:20:35.913 19310-19310/? E/AndroidRuntime: FATAL EXCEPTION: main
                                                   Process: com.supercilex.robotscouter.debug, PID: 19310
                                                   java.lang.IllegalStateException: Could not resolve type T
                                                       at com.google.android.gms.internal.zzamy$zza.zza(Unknown Source)
                                                       at com.google.android.gms.internal.zzamy$zza.zze(Unknown Source)
                                                       at com.google.android.gms.internal.zzamy$zza.zzce(Unknown Source)
                                                       at com.google.android.gms.internal.zzamy.zze(Unknown Source)
                                                       at com.google.android.gms.internal.zzamy.zzb(Unknown Source)
                                                       at com.google.android.gms.internal.zzamy.zza(Unknown Source)
                                                       at com.google.android.gms.internal.zzamy.zza(Unknown Source)
                                                       at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
                                                       at com.supercilex.robotscouter.scout.ScoutFragment$1.parseSnapshot(ScoutFragment.java:91)
                                                       at com.supercilex.robotscouter.scout.ScoutFragment$1.parseSnapshot(ScoutFragment.java:67)
                                                       at com.supercilex.robotscouter.FirebaseRecyclerAdapter.getItem(FirebaseRecyclerAdapter.java:155)
                                                       at com.supercilex.robotscouter.scout.ScoutFragment$1.getItemViewType(ScoutFragment.java:139)
                                                       at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5017)
                                                       at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4970)
                                                       at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2029)
                                                       at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1414)
                                                       at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1377)
                                                       at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:578)
                                                       at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3315)
                                                       at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3124)
                                                       at android.support.v7.widget.RecyclerView.consumePendingUpdateOperations(RecyclerView.java:1549)
                                                       at android.support.v7.widget.RecyclerView$1.run(RecyclerView.java:305)
                                                       at android.view.Choreographer$CallbackRecord.run(Choreographer.java:871)
                                                       at android.view.Choreographer.doCallbacks(Choreographer.java:683)
                                                       at android.view.Choreographer.doFrame(Choreographer.java:616)
                                                       at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:857)
                                                       at android.os.Handler.handleCallback(Handler.java:751)
                                                       at android.os.Handler.dispatchMessage(Handler.java:95)
                                                       at android.os.Looper.loop(Looper.java:154)
                                                       at android.app.ActivityThread.main(ActivityThread.java:6077)
                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

【问题讨论】：

标签： java android generics firebase firebase-realtime-database

【解决方案1】：

我在我的应用程序中遇到了同样的问题。我在这个答案中与杰克逊一起解决了：

Android Firebase Exception "Could not resolve type T"

像这样：

ObjectMapper mapper = new ObjectMapper();
ScoutSpinner spinner = mapper.convertValue(dataSnapshot.getValue(), ScoutSpinner.class);

【讨论】：