解决android.support.v4.content.FileProvide找不到的问题

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
 }

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。

来源：https://blog.csdn.net/boxin1101/article/details/89643396