Android N调用系统安装APK方法报错缘由整理及解决方案

最近在作App的改版（由系统App改成普通App）过程当中，经原来的静默安装方式改成调用系统普通安装APK的方式时，报错了，堆栈信息以下：

fatal error
java.lang.IllegalArgumentException: Failed to find configured root that contains /storage/emulated/0/Android/data/com.xxx.xxx/cache/com.aaa.bbb.apk
at android.support.v4.content.FileProvider$SimplePathStrategy.getUriForFile(FileProvider.java:738)
at android.support.v4.content.FileProvider.getUriForFile(FileProvider.java:417)
at com.xxx.xxx.service.download.ApkDownloadHelper.installApp(ApkDownloadHelper.java:299)
at com.xxx.xxx.service.download.ApkDownloadHelper.checkForInstall(ApkDownloadHelper.java:233)
at com.xxx.xxx.service.download.ApkDownloadHelper.onSuccess(ApkDownloadHelper.java:220)
at com.xxx.xxx.download.FileDownloader.notifySuccess(FileDownloader.java:246)
at com.xxx.xxx.download.FileDownloader.onResponse(FileDownloader.java:197)
at okhttp3.RealCall$AsyncCall.execute(RealCall.java:153)
at okhttp3.internal.NamedRunnable.run(NamedRunnable.java:32)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
at java.lang.Thread.run(Thread.java:764)

Failed to find configured root that……

这里的意思是说：没有找到根目录的配置。

接下来，咱们查阅FileProvider.java源文件，发现有一个常量定义

private static final String TAG_ROOT_PATH = "root-path";

紧接着，咱们寻找使用这个变量的地方，在文件第620行找到，以下：

private static PathStrategy parsePathStrategy(Context context, String authority)
        throws IOException, XmlPullParserException {
    final SimplePathStrategy strat = new SimplePathStrategy(authority);

    final ProviderInfo info = context.getPackageManager()
            .resolveContentProvider(authority, PackageManager.GET_META_DATA);
    final XmlResourceParser in = info.loadXmlMetaData(
            context.getPackageManager(), META_DATA_FILE_PROVIDER_PATHS);
    if (in == null) {
        throw new IllegalArgumentException(
                "Missing " + META_DATA_FILE_PROVIDER_PATHS + " meta-data");
    }

    int type;
    while ((type = in.next()) != END_DOCUMENT) {
        if (type == START_TAG) {
            final String tag = in.getName();

            final String name = in.getAttributeValue(null, ATTR_NAME);
            String path = in.getAttributeValue(null, ATTR_PATH);

            File target = null;
            
            if (TAG_ROOT_PATH.equals(tag)) {
                target = DEVICE_ROOT;
            } else if (TAG_FILES_PATH.equals(tag)) {
                target = context.getFilesDir();
            } else if (TAG_CACHE_PATH.equals(tag)) {
                target = context.getCacheDir();
            } else if (TAG_EXTERNAL.equals(tag)) {

这个方法主要是“分析路径策略”，主要是解析manifest中配置的provider的meta-data属性中的resource中file_paths文件。

<provider android:name="android.support.v4.content.FileProvider" android:authorities="${applicationId}.provider" android:exported="false" android:grantUriPermissions="true">
    <meta-data android:name="android.support.FILE_PROVIDER_PATHS" android:resource="@xml/file_paths" />
</provider>

Android N开始，Google逐步提升了系统的安全性，其中包括文件的访问。因此从Android N开始，提升了文件访问的门槛，须要再file_paths中增长以下配置：

<?xml version="1.0" encoding="utf-8"?>
<paths>
    <!--Context.getFilesDir()位于/data/data/安装目录-->
    <files-path name="internalPath" path="file" />
    <!--Context.getCacheDir()-->
    <cache-path name="cachePath" path="file" />
    <!--Environment.getExternalStorageDirectory()-->
    <external-path name="externalPath" path="file" />
    <!--Context.getExternalFilesDir(null)-->
    <external-files-path name="externalPath" path="file" />

    <external-cache-path name="externalCachePath" path="file" />
	<!--增长根目录配置，特别注意：此处的path要为空字符串-->
    <root-path name="rootPath" path="" />
</paths>

这样，咱们就能够解决一开始抛出的文件。

欢迎你们在评论区留言，一块儿交流，谢谢。