android - Android objectBox.getAll()返回null，即使objectBox.count为5

我不明白为什么for循环会破坏我的应用程序。我知道这是一个简单的问题，但我已经盯着这段代码看了好几个小时试图找出答案。我非常确定build.gradle中的所有依赖项都是正确的。如果你需要更多的信息请告诉我。谢谢您。
//app类

package edu.uncw.seahawktours;

import android.app.Application;

import java.util.ArrayList;
import java.util.List;

import io.objectbox.Box;
import io.objectbox.BoxStore;

public class App extends Application {

private BoxStore boxStore;

@Override
public void onCreate() {
    super.onCreate();

    // Initialize the main data access object
    boxStore = MyObjectBox.builder().androidContext(App.this).build();

    // Get the wrapper (Box) for the Book table that lets us store Book objects
    Box<Building> buildingBox = boxStore.boxFor(Building.class);

    // Initialize with some data
    if (buildingBox.count() == 0) {
        List<Building> initialBooks = new ArrayList<>();
        initialBooks.add(new Building("CIS", "https://library.uncw.edu/web/collections/archives/bnl/cis.html", R.drawable.cis));
        initialBooks.add(new Building("Depaolo Hall", "https://library.uncw.edu/web/collections/archives/bnl/6.html", R.drawable.depaolo));
        initialBooks.add(new Building("Trask Coliseum", "https://library.uncw.edu/web/collections/archives/bnl/10.html", R.drawable.trask));
        initialBooks.add(new Building("King Hall", "https://library.uncw.edu/web/collections/archives/bnl/4.html", R.drawable.kinghall2));
        initialBooks.add(new Building("Leutze Hall", "https://library.uncw.edu/web/collections/archives/bnl/17.html", R.drawable.leutzehall));

        // ObjectBox is smart enough to handle CRUD on Collections of entities
        buildingBox.put(initialBooks);
    }

    System.out.println(buildingBox.count());

    for (Building book : buildingBox.getAll()) {
        System.out.println(book.getBuildingName());
    }

}

public BoxStore getBoxStore() {
    return boxStore;
    }
}

//building类

package edu.uncw.seahawktours;

import io.objectbox.annotation.Entity;
import io.objectbox.annotation.Id;

@Entity
public class Building {
    @Id public long id;
    private String buildingName;
    private String description;
    private String url;
    private int imageID;


public Building(String name, String url ,int buildingPictureID){
    this.buildingName = name;
    this.url = url;
    this.imageID = buildingPictureID;
}

public long getId() {
    return id;
}

public String getDescription() {
    return description;
}

public String getBuildingName() {
    return buildingName;
}

public String getUrl() {
    return url;
}

public int getImageID() {
    return imageID;
}

public void setId(long id) {
    this.id = id;
}

public void setBuildingName(String buildingName) {
    this.buildingName = buildingName;
}

public void setDescription(String description) {
    this.description = description;
}

public void setUrl(String url) {
    this.url = url;
}

public void setImageID(int imageID) {
    this.imageID = imageID;
}

@Override
public String toString() {
    return this.buildingName;
    }
}

//project build.gradle项目

// Top-level build file where you can add configuration options common to
all sub-projects/modules.

buildscript {
    ext.objectboxVersion = '2.2.0'
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.2.0'
        classpath "io.objectbox:objectbox-gradle-plugin:$objectboxVersion"


    // NOTE: Do not place your application dependencies here; they belong
    // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

//app build.gradle版本

apply plugin: 'com.android.application'
apply plugin: 'io.objectbox'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "edu.uncw.seahawktours"
        minSdkVersion 19
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.android.support:design:28.0.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support:recyclerview-v7:28.0.0'
    implementation 'com.android.support:cardview-v7:28.0.0'
}

最佳答案

我的答案很糟糕，但objectbox只适合“平面”数据结构。关系实现很糟糕，就像realmdb一样糟糕。为什么我们不能嵌入对象，为什么所有的东西都是关系？还有一个慢得多的选择，Couchbase Mobile。它几乎不被提及，但更像是移动版的MongoDB。我以前试过，不喜欢它-我仍然不喜欢它，但我不必花很多天试图找到文件，使它工作。只需保存数据结构。它不像objectbox那样类型安全（很糟糕）。似乎所有的产品都有不同程度的缺陷。
所以考虑一下：
objectbox对于平面结构和性能来说是最好的，但是与服务器响应的集成是很糟糕的（您必须为很多简单的事情编写大量的boiler plate，比如更新太多的关联-toone，并且文档对于kotlin和java都很糟糕）
realmdb有可怕的多线程问题，它比objectbox慢，但比couchbase mobile快得多。
couchbase移动性能很差，但当您从服务器接收到服务器结构时，可以存储它们。如果couchbase mobile修复了它们的查询/插入性能，那么当它根据需要存储对象结构时（例如，一个映射），它将粉碎其他的性能。
我知道这没用，投我一票，但我花了一段时间玩所有这些，仍然没有一个明确的路径离线存储为基础的应用程序。