Android资源文件中特殊字符未转义引起的编译错误

     给一使用了Android做上位机的操作系统的机器人写安卓代码+JNI代码以访问电机硬件设备，代码写了一堆编译时出如下的错，错误里没说明白原因是什么，clean+build或直接rebuild之类的折腾了没效果，琢磨了一阵没想到是什么原因，郁闷抓狂不已：

org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':RobotExam:mergeDebugResources'.
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:100)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:70)
    at org.gradle.api.internal.tasks.execution.OutputDirectoryCreatingTaskExecuter.execute(OutputDirectoryCreatingTaskExecuter.java:51)
    at org.gradle.api.internal.tasks.execution.SkipUpToDateTaskExecuter.execute(SkipUpToDateTaskExecuter.java:62)
    at org.gradle.api.internal.tasks.execution.ResolveTaskOutputCachingStateExecuter.execute(ResolveTaskOutputCachingStateExecuter.java:54)
    at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:60)
    at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:97)
    at org.gradle.api.internal.tasks.execution.CleanupStaleOutputsExecuter.execute(CleanupStaleOutputsExecuter.java:87)
    at org.gradle.api.internal.tasks.execution.ResolveTaskArtifactStateTaskExecuter.execute(ResolveTaskArtifactStateTaskExecuter.java:52)
    at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:52)
    at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:54)
    at org.gradle.api.internal.tasks.execution.ExecuteAtMostOnceTaskExecuter.execute(ExecuteAtMostOnceTaskExecuter.java:43)
    at org.gradle.api.internal.tasks.execution.CatchExceptionTaskExecuter.execute(CatchExceptionTaskExecuter.java:34)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker$1.run(DefaultTaskGraphExecuter.java:248)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:336)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:328)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:199)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:110)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker.execute(DefaultTaskGraphExecuter.java:241)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker.execute(DefaultTaskGraphExecuter.java:230)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker.processTask(DefaultTaskPlanExecutor.java:123)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker.access$200(DefaultTaskPlanExecutor.java:79)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker$1.execute(DefaultTaskPlanExecutor.java:104)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker$1.execute(DefaultTaskPlanExecutor.java:98)
    at org.gradle.execution.taskgraph.DefaultTaskExecutionPlan.execute(DefaultTaskExecutionPlan.java:626)
    at org.gradle.execution.taskgraph.DefaultTaskExecutionPlan.executeWithTask(DefaultTaskExecutionPlan.java:581)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker.run(DefaultTaskPlanExecutor.java:98)
    at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63)
    at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55)
    at java.lang.Thread.run(Thread.java:745)
Caused by: com.android.build.gradle.tasks.ResourceException: Error: java.util.concurrent.ExecutionException: com.android.builder.internal.aapt.v2.Aapt2Exception: AAPT2 error: check logs for details
    at com.android.build.gradle.tasks.MergeResources.doIncrementalTaskAction(MergeResources.java:392)
    at com.android.build.gradle.internal.tasks.IncrementalTask.taskAction(IncrementalTask.java:110)
    at sun.reflect.GeneratedMethodAccessor235.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:73)
    at org.gradle.api.internal.project.taskfactory.IncrementalTaskAction.doExecute(IncrementalTaskAction.java:46)
    at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:39)
    at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:26)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$1.run(ExecuteActionsTaskExecuter.java:121)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:336)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:328)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:199)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:110)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:110)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:92)
    ... 32 more
Caused by: Error: java.util.concurrent.ExecutionException: com.android.builder.internal.aapt.v2.Aapt2Exception: AAPT2 error: check logs for details
    at com.android.ide.common.res2.MergedResourceWriter.end(MergedResourceWriter.java:332)
    at com.android.ide.common.res2.DataMerger.mergeData(DataMerger.java:301)
    at com.android.ide.common.res2.ResourceMerger.mergeData(ResourceMerger.java:412)
    at com.android.build.gradle.tasks.MergeResources.doIncrementalTaskAction(MergeResources.java:381)
    ... 47 more
    Suppressed: java.lang.RuntimeException: Some file processing failed, see logs for details
        at com.android.builder.internal.aapt.QueuedResourceProcessor.waitForAll(QueuedResourceProcessor.java:121)
        at com.android.builder.internal.aapt.QueuedResourceProcessor.end(QueuedResourceProcessor.java:141)
        at com.android.builder.internal.aapt.v2.QueueableAapt2.close(QueueableAapt2.java:104)
        at com.android.build.gradle.tasks.MergeResources.doIncrementalTaskAction(MergeResources.java:389)
        ... 47 more
Caused by: java.util.concurrent.ExecutionException: java.util.concurrent.ExecutionException: com.android.builder.internal.aapt.v2.Aapt2Exception: AAPT2 error: check logs for details
    at com.google.common.util.concurrent.AbstractFuture.getDoneValue(AbstractFuture.java:503)
    at com.google.common.util.concurrent.AbstractFuture.get(AbstractFuture.java:482)
    at com.google.common.util.concurrent.AbstractFuture$TrustedFuture.get(AbstractFuture.java:79)
    at com.android.ide.common.res2.MergedResourceWriter.end(MergedResourceWriter.java:327)
    ... 50 more
Caused by: java.util.concurrent.ExecutionException: com.android.builder.internal.aapt.v2.Aapt2Exception: AAPT2 error: check logs for details
    at com.google.common.util.concurrent.AbstractFuture.getDoneValue(AbstractFuture.java:503)
    at com.google.common.util.concurrent.AbstractFuture.get(AbstractFuture.java:462)
    at com.google.common.util.concurrent.AbstractFuture$TrustedFuture.get(AbstractFuture.java:79)
    at com.android.builder.internal.aapt.v2.QueueableAapt2.lambda$compile$0(QueueableAapt2.java:136)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    ... 1 more
Caused by: com.android.builder.internal.aapt.v2.Aapt2Exception: AAPT2 error: check logs for details
    at com.android.builder.png.AaptProcess$NotifierProcessOutput.handleOutput(AaptProcess.java:443)
    at com.android.builder.png.AaptProcess$NotifierProcessOutput.err(AaptProcess.java:395)
    at com.android.builder.png.AaptProcess$ProcessOutputFacade.err(AaptProcess.java:312)
    at com.android.utils.GrabProcessOutput$1.run(GrabProcessOutput.java:104)

后来把错误展开仔细看错误中的每行，发现这句：

Caused by: com.android.build.gradle.tasks.ResourceException: Error: java.util.concurrent.ExecutionException: com.android.builder.internal.aapt.v2.Aapt2Exception: AAPT2 error: check logs for details
    at com.android.build.gradle.tasks.MergeResources.doIncrementalTaskAction(MergeResources.java:392)

     这里反复提到了resource，看来似乎跟resource文件有关，于是把UI代码中跟resource有关的代码都注释掉，把对应的res/layout/下的 xml文件备份后删掉，再build发现过了，看来应该是这个layout xml文件内容写得有毛病，里面控件很多啊，问题处在哪里呢？初看似乎没啥问题，语法都是正确的，控件在设计模式下都能正常显示出来，奇怪，于是用了个笨办法，把一个个控件删掉，每次删掉一个控件后都编译一次，知道编译成功或出现另外都错误，果然发现，把下面的textview控件删掉后:

        android:id="@+id/tv_rpm"
        android:layout_width="88dp"
        android:layout_height="36dp"
        android:layout_toRightOf="@+id/btn_startmotor"
        android:layout_marginTop="20dp"
        android:layout_marginLeft="20dp"
        android:width="100dp"
        android:text="rpm(<350)"
        android:visibility="visible" />

报的错误就不一样了：

      错误: 找不到符号
      符号:   变量 btn_stopmotor
      位置: 类 id

      错误: 找不到符号
      符号:   变量 tv_state
      位置: 类 id

      错误: 找不到符号
      符号:   变量 tv_state_rpm
      位置: 类 id

上面这些错误好说，都是因为我把他们在layout xml里的定义删掉了，这就说明删掉上面的textview控件后编译可以过了，那说明这个textview的定义有毛病，于是再仔细看了一下，其他的地方没啥怀疑的，唯一值得怀疑的就是"rpm(<350)"，于是把<符号删掉试试，果然，整个项目都可以编译过了！靠，原来大意掉坑里了！我知道特殊字符可能需要转义，这里都有提到过：

https://www.utf8-chartable.de/unicode-utf8-table.pl?number=1024&utf8=0x

https://www.jianshu.com/p/b6c3502bf4ba

不过以前我在textview之类控件都text属性里直接使用= 或 > 也没见编译错误，偏这个<就不行，改成"rpm(<350)"果然编译没问题了！ 以后得记住这个坑不能懒不能大意，否则找错误浪费时间啊！另外，res/values/string.xml之类文件里定义文本字符串时也需要注意同样的问题哦。