当加载Google时，您可以侦听'loaderror'事件地图图块失败。以下是常规WMS图层的示例（完整示例，位于 http://jsfiddle.net/D3Eha/2/）

You can listen for 'loaderror' event, that will be thrown, when loading of Google Map tile fails. Here is example with regular WMS layer (full example in http://jsfiddle.net/D3Eha/2/)

var wmsLayer, workingOffline = false;

wmsLayer = new OpenLayers.Layer.WMS("OpenLayers WMS",
    "http://vmap0.tiles.osgeo.org/wms/vmap0?",
    {layers: 'basic'},
    {
        attribution: 'Provided by OSGeo',
        tileOptions: {
            eventListeners: {
                'loaderror': function(evt) {
                    if (workingOffline == false) {
                        console.log('Tile load error, switching to offline map');
                        workingOffline = true;
                    }
                }
            }
        }        
    }
);

当计算机再次联机时，检测是非常棘手的。例如，当你离线时，启动定期计时器从Internet加载一些图像。如果成功，您将重新上线。

It's trickier to detect, when computer is online again. For example, when you go offline, start periodical timer to load some image from Internet. If it succeeds, you are back online.