private void installApk(String apkPath) {
    File apkFile = new File(apkPath);
    if (!apkFile.exists()) {
        Toast.makeText(this, "APK文件不存在", Toast.LENGTH_SHORT).show();
        return;
    }

    Uri apkUri;
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
        apkUri = FileProvider.getUriForFile(this, BuildConfig.APPLICATION_ID + ".provider", apkFile);
        Intent intent = new Intent(Intent.ACTION_INSTALL_PACKAGE);
        intent.setData(apkUri);
        intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        startActivity(intent);
    } else {
        apkUri = Uri.fromFile(apkFile);
        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setDataAndType(apkUri, "application/vnd.android.package-archive");
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        startActivity(intent);
    }
}

<provider
    android:name="androidx.core.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>

<paths>
    <external-path name="external_files" path="." />
</paths>