在ListView中列出可用的Bluetooth设备但未显示ListView

I want to create a app that can send data with Bluetooth to another device. First I made a Button to turn Bluetooth on and off. That works smoothly! Now I included a ListView that should list available yet unpaired devices, but the ListView is not showing. I searched for a solution but I coulnd't find anything. I don't get any Event Log and I don't know what I should do. I tried many different things but in the end my app just kept crashing. Here is my code:I want to create a app that can send data with