我有一个模特：
12-12 15:01:18.436 27069-27069/com.platinum.hydro E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.platinum.hydro, PID: 27069
java.lang.NoClassDefFoundError: Failed resolution of: Landroid/support/v4/util/ArrayMap;
at com.google.firebase.FirebaseApp.<clinit>(Unknown Source)
at com.google.firebase.provider.FirebaseInitProvider.onCreate(Unknown Source)
at android.content.ContentProvider.attachInfo(ContentProvider.java:1751)
at android.content.ContentProvider.attachInfo(ContentProvider.java:1726)
at com.google.firebase.provider.FirebaseInitProvider.attachInfo(Unknown Source)
at android.app.ActivityThread.installProvider(ActivityThread.java:5319)
at android.app.ActivityThread.installContentProviders(ActivityThread.java:4893)
at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4833)
at android.app.ActivityThread.access$1500(ActivityThread.java:178)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1531)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5631)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754)
Caused by: java.lang.ClassNotFoundException: Didn't find class "android.support.v4.util.ArrayMap" on path: DexPathList[[zip file "/data/app/com.platinum.hydro-2/base.apk"],nativeLibraryDirectories=[/data/app/com.platinum.hydro-2/lib/arm, /vendor/lib, /system/lib]]
at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
at com.google.firebase.FirebaseApp.<clinit>(Unknown Source)
at com.google.firebase.provider.FirebaseInitProvider.onCreate(Unknown Source)
at android.content.ContentProvider.attachInfo(ContentProvider.java:1751)
at android.content.ContentProvider.attachInfo(ContentProvider.java:1726)
at com.google.firebase.provider.FirebaseInitProvider.attachInfo(Unknown Source)
at android.app.ActivityThread.installProvider(ActivityThread.java:5319)
at android.app.ActivityThread.installContentProviders(ActivityThread.java:4893)
at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4833)
at android.app.ActivityThread.access$1500(ActivityThread.java:178)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1531)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5631)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754)
Suppressed: java.lang.ClassNotFoundException: android.support.v4.util.ArrayMap
at java.lang.Class.classForName(Native Method)
at java.lang.BootClassLoader.findClass(ClassLoader.java:781)
at java.lang.BootClassLoader.loadClass(ClassLoader.java:841)
at java.lang.ClassLoader.loadClass(ClassLoader.java:504)
... 18 more
Caused by: java.lang.NoClassDefFoundError: Class not found using the boot class loader; no stack available
据我所知，每次public class Genre : DbObject
{
public string GenreName { get; set; }
public virtual ICollection<Book> Books { get; set; } = new List<Book>();
public virtual int BooksCount => Books.Count;
}
都是对数据库的请求，以计算BooksCount集合中的对象数。也许只有在集合发生变化时才会在数据库中更改属性Books的方法？