在AndroidManifest.xml中加入下面这段话后，

<provider
      android:name="android.support.v4.content.FileProvider"
      android:authorities="com.boxin.forklift.fileprovider"
      android:exported="false"
      android:grantUriPermissions="true" 
      <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_paths" / 
    </provider 

在Android4.4.2版本的手机出现了下面的错误提示

E/AndroidRuntime: FATAL EXCEPTION: main
  Process: com.boxin.forklift, PID: 7106
  java.lang.RuntimeException: Unable to get provider android.support.v4.content.FileProvider: java.lang.ClassNotFoundException: Didn't find class "android.support.v4.content.FileProvider" on path: DexPathList[[zip file "/data/app/com.boxin.forklift-1.apk"],nativeLibraryDirectories=[/data/app-lib/com.boxin.forklift-1, /vendor/lib, /system/lib, /data/datalib]]
    at android.app.ActivityThread.installProvider(ActivityThread.java:5045)
    at android.app.ActivityThread.installContentProviders(ActivityThread.java:4631)
    at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4571)
    at android.app.ActivityThread.access$1700(ActivityThread.java:143)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1304)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:136)
    at android.app.ActivityThread.main(ActivityThread.java:5291)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:515)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
    at dalvik.system.NativeStart.main(Native Method)
   Caused by: java.lang.ClassNotFoundException: Didn't find class "android.support.v4.content.FileProvider" on path: DexPathList[[zip file "/data/app/com.boxin.forklift-1.apk"],nativeLibraryDirectories=[/data/app-lib/com.boxin.forklift-1, /vendor/lib, /system/lib, /data/datalib]]
    at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:497)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:457)
    at android.app.ActivityThread.installProvider(ActivityThread.java:5030)
    at android.app.ActivityThread.installContentProviders(ActivityThread.java:4631) 
    at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4571) 
    at android.app.ActivityThread.access$1700(ActivityThread.java:143) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1304) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:136) 
    at android.app.ActivityThread.main(ActivityThread.java:5291) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665) 
    at dalvik.system.NativeStart.main(Native Method) 

解决方案：

第一：可能是添加MultiDex分包，但未初始化的原因，在Application中重写attachBaseContext函数，对MultiDex初始化即可。

1）首先修改Gradle配置文件，启用MultiDex并包含MultiDex支持：

   defaultConfig {
     multiDexEnabled true
  }

项目完整写法：

android {
  compileSdkVersion 27
  defaultConfig {
    applicationId "com.boxin.forklift"
    minSdkVersion 19
    targetSdkVersion 27
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    multiDexEnabled true