Android N安装apk报错：android.os.FileUriExposedException

StackOverflow: http://stackoverflow.com/questions/38200282/android-os-fileuriexposedexception-file-storage-emulated-0-test-txt-exposed

1.在AndroidMainifest.xml文件中添加:

<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/provider_paths"/>
</provider>

###:

authorities：app的包名.fileProvider 
grantUriPermissions：true，表示授予 URI 临时访问权限 
exported：false 
resource：下一步添加的文件

2.在res下新建一个名为xml的文件家，再新建文件provider_paths:

<?xml version="1.0" encoding="utf-8"?>
<paths>
    <external-path
        name="files_root"
        path="Android/data/com.example.downloadapk/"/>
    <external-path
        name="external_storage_root"
        path="."/>
</paths>

###：

path：需要临时授权访问的路径（.代表所有路径） 
name：给访问路径命名

3.安装apk文件:

   /**
     * 安装apk文件
     *
     * @param apkFile 安装包所在目录
     */
    private void installApk(File apkFile) {
        Intent intent = new Intent(Intent.ACTION_VIEW);
        try {
            String[] command = {"chmod", "777", apkFile.toString()};
            ProcessBuilder builder = new ProcessBuilder(command);
            builder.start();
        } catch (IOException ignored) {
        }

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            intent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
            Uri contentUri = FileProvider.getUriForFile(getApplicationContext(),
                    BuildConfig.APPLICATION_ID + ".fileProvider", apkFile);
            intent.setDataAndType(contentUri, "application/vnd.android.package-archive");
        } else {
            intent.setDataAndType(Uri.fromFile(apkFile), "application/vnd.android.package-archive");
            intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        }

        startActivity(intent);
    }