android/app/download_model.gradle

task downloadZipFile(type: Download) {
    src 'http://storage.googleapis.com/download.tensorflow.org/models/tflite/coco_ssd_mobilenet_v1_1.0_quant_2018_06_29.zip'
    dest new File(buildDir, 'zips/')
    overwrite false
}


task downloadAndUnzipFile(dependsOn: downloadZipFile, type: Copy) {
    from zipTree(downloadZipFile.dest)
    into project.ext.ASSET_DIR
}


task extractModels(type: Copy) {
    dependsOn downloadAndUnzipFile
}

tasks.whenTaskAdded { task ->
    if (task.name == 'assembleDebug') {
        task.dependsOn 'extractModels'
    }
    if (task.name == 'assembleRelease') {
        task.dependsOn 'extractModels'
    }
}