断网使用RycyclerView的jar包，运行时报错

我在android工程的libs文件中加入RecycerView的jar包，运行后出现以下错误：

05-23 11:40:47.179 30641-30641/com.example.fan.uibestpractice E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.fan.uibestpractice, PID: 30641
    java.lang.RuntimeException: Unable to start activity ComponentInfo

{com.example.fan.uibestpractice/com.example.fan.uibestpractice.MainActivity}: 

android.view.InflateException: Binary XML file line #9: Binary XML file line #9: Error inflating class 

android.support.v7.widget.RecyclerView
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3303)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3411)
        at android.app.ActivityThread.-wrap12(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1994)
        at android.os.Handler.dispatchMessage(Handler.java:108)
        at android.os.Looper.loop(Looper.java:166)
        at android.app.ActivityThread.main(ActivityThread.java:7529)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
     Caused by: android.view.InflateException: Binary XML file line #9: Binary XML file line #9: Error 

inflating class android.support.v7.widget.RecyclerView
     Caused by: android.view.InflateException: Binary XML file line #9: Error inflating class 

android.support.v7.widget.RecyclerView
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Constructor.newInstance0(Native Method)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:334)
        at android.view.LayoutInflater.createView(LayoutInflater.java:658)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:801)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:741)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:874)
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:835)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
        at android.support.v7.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:469)
        at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140)
        at com.example.fan.uibestpractice.MainActivity.onCreate(MainActivity.java:21)
        at android.app.Activity.performCreate(Activity.java:7383)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1218)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3256)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3411)
        at android.app.ActivityThread.-wrap12(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1994)
        at android.os.Handler.dispatchMessage(Handler.java:108)
        at android.os.Looper.loop(Looper.java:166)
        at android.app.ActivityThread.main(ActivityThread.java:7529)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
     Caused by: java.lang.NoClassDefFoundError: Failed resolution of: Landroid/support/v7/recyclerview/R

$styleable;
        at android.support.v7.widget.RecyclerView.<init>(RecyclerView.java:691)
        at android.support.v7.widget.RecyclerView.<init>(RecyclerView.java:647)
        at java.lang.reflect.Constructor.newInstance0(Native Method) 
        at java.lang.reflect.Constructor.newInstance(Constructor.java:334) 
        at android.view.LayoutInflater.createView(LayoutInflater.java:658) 
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:801) 
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:741) 
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:874) 
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:835) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:515) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:423) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:374) 
        at android.support.v7.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:469) 
        at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140) 
        at com.example.fan.uibestpractice.MainActivity.onCreate(MainActivity.java:21) 
        at android.app.Activity.performCreate(Activity.java:7383) 
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1218) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3256) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3411) 
        at android.app.ActivityThread.-wrap12(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1994) 
        at android.os.Handler.dispatchMessage(Handler.java:108) 
        at android.os.Looper.loop(Looper.java:166) 
        at android.app.ActivityThread.main(ActivityThread.java:7529) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921) 
    Caused by: java.lang.ClassNotFoundException: Didn't find class "android.support.v7.recyclerview.R

$styleable" on path: DexPathList[[zip file "/data/app/com.example.fan.uibestpractice-

vYH2dgzPueilqQNMspxfSw==/base.apk", zip file "/data/app/com.example.fan.uibestpractice-

vYH2dgzPueilqQNMspxfSw==/split_lib_dependencies_apk.apk", zip file 

"/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_resources_apk.apk", zip 

file "/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_slice_0_apk.apk", zip 

file "/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_slice_1_apk.apk", zip 

file "/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_slice_2_apk.apk", zip 

file "/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_slice_3_apk.apk", zip 

file "/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_slice_4_apk.apk", zip 

file "/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_slice_5_apk.apk", zip 

file "/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_slice_6_apk.apk", zip 

file "/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_slice_7_apk.apk", zip 

file "/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_slice_8_apk.apk", zip 

file "/data/app/com.example.fan.uibestpractice-

vYH2dgzPueilqQNMspxfSw==/split_lib_slice_9_apk.apk"],nativeLibraryDirectories=

[/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/lib/arm64, /system/lib64, 

/vendor/lib64, /product/lib64]]
        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:93)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
        	... 27 more
    	Suppressed: java.io.IOException: No original dex files found for dex location 

/data/app/com.example.fan.uibestpractice-vYH2dgzPueilqQNMspxfSw==/split_lib_resources_apk.apk
        at dalvik.system.DexFile.openDexFileNative(Native Method)
        at dalvik.system.DexFile.openDexFile(DexFile.java:353)
        at dalvik.system.DexFile.<init>(DexFile.java:100)
        at dalvik.system.DexFile.<init>(DexFile.java:74)
        at dalvik.system.DexPathList.loadDexFile(DexPathList.java:374)
        at dalvik.system.DexPathList.makeDexElements(DexPathList.java:337)
        at dalvik.system.DexPathList.<init>(DexPathList.java:157)
        at dalvik.system.BaseDexClassLoader.<init>(BaseDexClassLoader.java:65)
        at dalvik.system.PathClassLoader.<init>(PathClassLoader.java:64)
        at com.android.internal.os.PathClassLoaderFactory.createClassLoader(PathClassLoaderFactory.java:43)
        at android.app.ApplicationLoaders.getClassLoader(ApplicationLoaders.java:75)
        at android.app.ApplicationLoaders.getClassLoader(ApplicationLoaders.java:38)
        at android.app.LoadedApk.createOrUpdateClassLoaderLocked(LoadedApk.java:719)
        at android.app.LoadedApk.getClassLoader(LoadedApk.java:752)
        at android.app.LoadedApk.getResources(LoadedApk.java:1005)
        at android.app.ContextImpl.createAppContext(ContextImpl.java:2489)
        at android.app.ActivityThread.handleBindApplication(ActivityThread.java:6497)
        at android.app.ActivityThread.-wrap2(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
        		... 6 more

看错误中

Caused by: java.lang.ClassNotFoundException: Didn't find class "android.support.v7.recyclerview.R

$styleable" on path:

可知由于编译时在路径中找不到"android.support.v7.recyclerview.R$styleable"报错的，查看我们的jar包已经导入成功，如下图所示：

原来该路径指向的不是Libs文件夹中recyclerview的jar包的路径，而是程序默认的jar包路径。在app/build.grdle文件中引入recyclerview依赖：。

implementation 'com.android.support:recyclerview-v7:28.0.0'

如下图所示：

注意版本号“28.0.0”要与你的项目中的appcompat-v7中的版本号保持一致，我的是28.0.0。此时我的电脑是断网状态的，点击【syn】同步app/buildgradle文件，程序将会把libs包中的recyclerview的jar包自动导入External Libraries目录，如下图：

此时运行仍会报错，因为项目中有两个recyclerview文件资源，编译器在编译时不知道要选哪一个。我们只需要将libs里的recyclerview的jar包删除掉，即：删除下图中的classes.jar。

点击编译，报错如下：

Transform output file D:\WorkSpace1\myDemo\UIBestPractice2\app\libs\classes.jar does not exist.

因为我们已经删除了classes.jar文件，但是没有在project structure的依赖包将它删掉，所以会报错，进入Project Structure将classes.jar依赖包删掉，再运行就没有任何错误了，接下来就可以正常使用recyclerview了。

step：1

step2:

由于我的工程所在的电脑不能联网，所有才使用离线jar包，有网的话直接在app/build.gradle中添加依赖：

implementation 'com.android.support:recyclerview-v7:28.0.0'

就可以用recyclerview了。

         最后，大家可能有个疑问，为什么recyclerview的jar包要放到External libraries路径中才能正常使用，一般离线jar包直接copy到libs文件夹中,再右键【add as library ...】就能用了。我觉得可能是因为Recyclerview涉及到UI操作，将jar包引入后，发现Recyclerview控件的后边存在一个下载的箭头，表示当前Recyclerview控件未下载，直接在布局中引用后运行就会报错。而在app/build.gradle中添加依赖后,Recyclerview控件的后边的下载箭头就消失了，表示Recyclerview控件已将载入到项目中，可以正常引用了。