一.清單檔案<application>內新增如下；

 <provider
            android:name="android.support.v4.content.FileProvider"
            android:authorities="包名.fileProvider"
            android:exported="false"
            android:grantUriPermissions="true">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/rc_file_path" />
        </provider>

二.res內建立XML資料夾新增一個rc_file_path.xml檔案如下；

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

三.mainactivity內程式碼如下；

 private void installApk() {
        String fileStoreDir = this.getExternalCacheDir().getPath();
        String fileName = "test" + "001" + ".apk";
        File file = new File(fileStoreDir, fileName);
        Intent intent = new Intent(Intent.ACTION_VIEW);
        if (Build.VERSION.SDK_INT >= N) {
            Uri apkUri = FileProvider.getUriForFile(MainActivity.this, "包名.fileProvider", file);
            intent.setDataAndType(apkUri, "application/vnd.android.package-archive");
            intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
        } else {
//                            intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            intent.setDataAndType(Uri.fromFile(file), "application/vnd.android.package-archive");
        }
        startActivity(intent);
    }