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Chapter 4. Implementation 61

Figure 4.21.: The visualization menu showing the database in receiver view.

reason, the visualization node contains a local copy of the database, in order to prevent high data

traﬃc to the device manager node and to speed up access times. In order to further increase

the overall performance, two QMultiHash containers were implemented to allow fast accessing

single elements of the QGraphicsScene, as it does not provide functions for eﬀectively searching

for items. QMultiHash is used, as devices can appear multiple times in the right column of the

tree model and consequently there can be multiple entries with the same name in the hash list.

As the QGraphicsScene is just a storage class for devices, the class QGraphicsView was used to

render and display the items. The order of items is random, because the QHash lists of the device

manager class are unsorted.

The visualization menu is connected via two signals to the device manager class: a device state

change notiﬁcation and a database change notiﬁcation. The database notiﬁcation indicates that a

device has been removed, added or changed and causes the QGraphicsView to completely redraw

the scene. The device state notiﬁcation implies that a transmitter has been seen and several

receivers have changed. Due to the QMultiHash containers, single updates are possible and the

whole scene need not be rendered completely.

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RFXCOM RFXtrx433 Spezifikationen Seite 68