浅析Android Wear App直接运行在手机上

一、编译&安装Wear Apk

1.1、源码下载

首先可以到Google官网Demo下载源码，本地编译几个WearApk，这里我选用AlwaysOn这个项目，就是展示时间等信息，比较简单。界面样式大概就这样：

img_1.png

1.2、项目结构

img_2.png

可以看到，跟普通的Android项目并没有什么不同，区别就是引入的包：

img_3.png

1.3、编译Apk

跟普通项目一样，通过Gradle编译即可。

1.4、安装

安装方式也是一样，直接通过adb install -r即可。

二、运行效果

经测试，在手机上，应用打开就会直接崩溃。Log如下：

04-27 14:45:35.942 E/AndroidRuntime(10278): Process: com.example.android.wearable.wear.alwayson, PID: 10278
04-27 14:45:35.942 E/AndroidRuntime(10278): java.lang.IllegalStateException: Could not find wearable shared library classes. Please add <uses-library android:name="com.google.android.wearable" android:required="false" /> to the application manifest
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.wear.ambient.SharedLibraryVersion.verifySharedLibraryPresent(SharedLibraryVersion.java:57)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.wear.ambient.WearableControllerProvider.getWearableController(WearableControllerProvider.java:48)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.wear.ambient.AmbientDelegate.onCreate(AmbientDelegate.java:103)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.wear.ambient.AmbientModeSupport.onCreate(AmbientModeSupport.java:198)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.Fragment.performCreate(Fragment.java:2414)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManager.java:1418)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1784)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManager.java:1852)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:802)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManager.java:2625)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2411)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2366)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2273)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManager.java:3273)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:3229)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:201)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:620)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1435)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.app.Activity.performStart(Activity.java:7864)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3366)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:221)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:201)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:173)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2077)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.os.Handler.dispatchMessage(Handler.java:107)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.os.Looper.loop(Looper.java:244)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at android.app.ActivityThread.main(ActivityThread.java:7539)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at java.lang.reflect.Method.invoke(Native Method)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
04-27 14:45:35.942 E/AndroidRuntime(10278):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1020)

三、原因分析

可以看到报错点主要是在SharedLibraryVersion.verifySharedLibraryPresent函数中，我们通过反编译看一下其中究竟做了什么：

public WearableActivityController getWearableController(Activity activity, final AmbientDelegate.AmbientCallback callback) {
        SharedLibraryVersion.verifySharedLibraryPresent();
        WearableActivityController.AmbientCallback callbackBridge = new WearableActivityController.AmbientCallback() {
            public void onEnterAmbient(Bundle ambientDetails) {
                callback.onEnterAmbient(ambientDetails);
            }

            public void onUpdateAmbient() {
                callback.onUpdateAmbient();
            }

            public void onExitAmbient() {
                callback.onExitAmbient();
            }

            public void onInvalidateAmbientOffload() {
                callback.onAmbientOffloadInvalidated();
            }
        };
        verifyAmbientCallbacksPresent();
        return new WearableActivityController(TAG, activity, callbackBridge);
    }

从函数名上，我们可以猜测，该函数是校验共享库是否存在并且可运行状态的。接下来我们来到：

public static void verifySharedLibraryPresent() {
        if (!PresenceHolder.PRESENT) {
            throw new IllegalStateException("Could not find wearable shared library classes. Please add <uses-library android:name=\"com.google.android.wearable\" android:required=\"false\" /> to the application manifest");
        }
    }

可以看到代码中抛出的IllegalStateException正是log中打印的

"Could not find wearable shared library classes. Please add <uses-library android:name="com.google.android.wearable" android:required="false" /> to the application manifest"

那是不是像Log中提示的一样，将这段 uses-library添加到AndroidManifest.xml中就可以运行了呢。我们来看下项目的配置文件：

img_4.png

原来这段代码已经添加，是为了让App跑在android-22之前而声明的，跟现在的报错并没有关系。

我们接着往下看吧，看看PresenceHolder.PRESENT是什么情况下会返回false。

img_5.png

看到这里，真相大白了！这是通过类加载的方式，检查系统预加载库中是否有包括类WearableActivityController，如果没有的话，证明系统中并没有内置wear相关的运行环境库，直接退出就可以了。

四、结论

手机跟手表必须内置Google Wear运行框架，Wear App才可以调用相关接口正常运行。此处可以参考小米手表，其内置了Google Play服务框架，以此来支持Android Wear的开发。这个也是小米手表跟OPPO Watch最大的区别。

而如何开发一个可以在国内正常使用，并且与手机正常通讯的Wear App，可以参考打造中国版 Wear OS 应用