Table 4. Yearly trends of the topics.

Topic name	2017	2018	2019	2020	2021	Trend
Flutter	0.78	1.68	3.36	5.61	6.58	5.88 ⇑
React-native	1.64	2.54	2.95	3.73	3.65	2.47 ⇑
Kotlin	3.92	4.37	4.68	4.83	4.68	1.12 ⇑
Error handling	3.51	3.87	4.33	3.88	4.27	1.03 ⇑
Project building	3.2	3.32	3.37	3.08	3.51	0.78 ⇑
Button actions	2.98	2.8	2.93	2.84	3.34	0.61 ⇑
Cloud firestore	1.02	1.36	1.49	1.74	1.65	0.56 ⇑
Authentication	3.74	3.56	3.82	3.76	4.12	0.41 ⇑
Android studio	5.03	5.28	4.86	4.56	4.98	0.38 ⇑
Threading	1.61	1.86	1.91	1.82	1.83	0.36 ⇑
Casting	2.73	2.69	2.74	2.89	3.08	0.22 ⇑
Testing	1.11	1.12	1.17	1.05	1.19	0.16 ⇑
Emulator	3.09	2.87	2.79	2.93	3.21	0.16 ⇑
File settings	2.43	2.47	2.46	2.46	2.59	0.14 ⇑
Navigation bar	2.33	2.29	2.29	2.35	2.27	0.01 ⇑
App crash	2.73	2.64	2.71	2.7	2.67	0.00 ⇑
Xamarin	1.45	1.39	1.39	1.49	1.21	−0.02 ⇓
Style-theme	2.76	2.72	2.83	2.85	2.77	−0.03 ⇓
Connection	2.90	2.69	2.51	2.34	2.53	−0.26 ⇓
Firebase	2.15	2.19	1.98	2.04	1.93	−0.27 ⇓
Media streaming	2.22	2.11	1.93	1.91	2.05	−0.34 ⇓
Dialog alerts	1.37	1.28	1.18	1.14	1.14	−0.36 ⇓
Functions	1.90	1.84	1.84	1.90	1.62	−0.49 ⇓
Text settings	3.11	3.02	2.98	2.76	2.63	−0.50 ⇓
Notifications	2.33	2.24	1.99	1.87	1.92	−0.72 ⇓
Web view	3.98	3.68	3.55	3.15	3.31	−0.72 ⇓
View controller	3.93	3.64	3.72	3.96	3.37	−0.79 ⇓
API requests	3.49	3.49	3.40	3.26	2.96	−0.89 ⇓
Imaging	3.82	3.65	3.37	3.17	3.02	−0.96 ⇓
List view	3.35	3.29	3.10	2.90	2.57	−1.00 ⇓
Arrays	4.67	4.63	4.40	4.40	3.87	−1.01 ⇓
Database tasks	2.50	2.42	2.16	1.91	1.62	−1.05 ⇓
Map API	2.57	2.29	2.10	1.73	1.69	−1.06 ⇓
Event issues	3.46	2.89	2.49	2.39	2.31	−1.18 ⇓
Fragment activity	2.86	2.63	2.39	2.19	1.86	−1.25 ⇓
Layout settings	3.31	3.2	2.81	2.41	2.01	−1.41 ⇓