Android如何确认一个Intent是否存在呢？

 /**
     * Indicates whether the specified action can be used as an intent. This
     * method queries the package manager for installed packages that can
     * respond to an intent with the specified action. If no suitable package is
     * found, this method returns false.
     *
     * @param context The application's environment.
     * @param action The Intent action to check for availability.
     *
     * @return True if an Intent with the specified action can be sent and
     * responded to, false otherwise.
     *  Example:isIntentAvailable(getApplicationContext(),Intent.ACTION_WEB_SEARCH)
     */
    public static boolean isIntentAvailable(Context context, String action) {
    final PackageManager packageManager = context.getPackageManager();
    final Intent intent = new Intent(action);
    List<ResolveInfo> list =
    packageManager.queryIntentActivities(intent,
    PackageManager.MATCH_DEFAULT_ONLY);
    return list.size() > 0;
    }