长按home键，代码调用栈如下：

123.png

主要源码逻辑：

AssistUtils::getAssistComponentForUser
public ComponentName getAssistComponentForUser(int userId) {
        final String setting = Settings.Secure.getStringForUser(mContext.getContentResolver(),
                Settings.Secure.ASSISTANT, userId);
        if (setting != null) {
            return ComponentName.unflattenFromString(setting);
        }

        //start, add by wangsenhao for cts, 2018.10.29
        String defaultSetting = mContext.getResources().getString(R.string.config_defaultAssistantComponentName);
                Log.d("assist", "defaultSetting:"+defaultSetting);
        if(android.os.SystemProperties.get("ro.hct_cts_go_support", "0").equals("1")){
            defaultSetting = "com.google.android.apps.assistant/com.google.android.apps.assistant.go.MainActivity";
        }
        if (defaultSetting != null) {
            return ComponentName.unflattenFromString(defaultSetting);
        }
        //end, add by wangsenhao for cts, 2018.10.29

        // Fallback to keep backward compatible behavior when there is no user setting.
        if (activeServiceSupportsAssistGesture()) {
            return getActiveServiceComponentName();
        }

        final SearchManager searchManager =
            (SearchManager) mContext.getSystemService(Context.SEARCH_SERVICE);
        if (searchManager == null) {
            return null;
        }
        final Intent intent = searchManager.getAssistIntent(false);
        PackageManager pm = mContext.getPackageManager();
        ResolveInfo info = pm.resolveActivityAsUser(intent, PackageManager.MATCH_DEFAULT_ONLY,
                userId);
        if (info != null) {
            return new ComponentName(info.activityInfo.applicationInfo.packageName,
                    info.activityInfo.name);
        }
        return null;
    }

AssistUtils::getAssistComponentForUser中返回的要拉起的component的优先级顺序如下：

第一优先级：从setting provider的数据获取
adb shell settings get secure assistant

第二优先级：从config文件配置获取：目前MTK平台的方式
String defaultSetting = mContext.getResources().getString(R.string.config_defaultAssistantComponentName);
Log.d("assist", "defaultSetting:"+defaultSetting);
Framework/…/Configg.xml

<string name="config_defaultAssistantComponentName" translatable="false">com.google.android.googlequicksearchbox/com.google.android.voiceinteraction.GsaVoiceInteractionService</string>

第三优先级：从mVoiceInteractionManagerService服务获取
if (activeServiceSupportsAssistGesture()) {
return getActiveServiceComponentName();
}

第四优先级，从apk自定义的Action获取#目前语音助手的方式

final Intent intent = searchManager.getAssistIntent(false);
PackageManager pm = mContext.getPackageManager();
ResolveInfo info = pm.resolveActivityAsUser(intent, PackageManager.MATCH_DEFAULT_ONLY,
userId);
if (info != null) {
return new ComponentName(info.activityInfo.applicationInfo.packageName,
info.activityInfo.name);
}
return null;

综上，长按home键应用或者项目建议实现方式：
方式一：语音助手，在手机启动时，去设置secure# assistant的值
方式二：提供配置的patch，提供给各个项目使用
<string name="config_defaultAssistantComponentName" translatable="false">………</string>