android.support.v4.content.FileProvide找不到的解决方法

在AndroidManifest.xml中加入下面这段话后，

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
    }

2）修改BoXinApplication,重写attachBaseContext方法
BoxinApplication默认的命名方式是：BaseApplication

@Override 
protected void attachBaseContext(Context base) { 
super.attachBaseContext(base); 
MultiDex.install(base); 
}

加入后成功运行项目到手机。