#Some notes:

###optimization

1. Use hardware to accelerate app. add android:hardwareAccelerated=”true” after appliation tag. It's activated by default after version Android 4.0.

2. Set View cacheable. setDrawingCache = "true"

3. <merge> avoid over-drawing layout, <include> shared layout.

4. Use files when you could do it. It's 10 times faster then doing SQL operation.

5. if no local member is invoked in a method, make it static, it will up performance by 15~20%.

6. Check memory limit per app.

   ` ActivityManager manager = (ActivityManager)this.getSystemService(Context.ACTIVITY_SERVICE);`
    `Log.d("Memory", manager.getMemoryClass() + "");`
   

7. Why Viewholder?

   ListView or RecyclerView could only call findbyId() limited times and then reuse the elements when list scrolled up or down.

   Tip: declare Viewholder with key word static, and it will reduce the amount of this calls from MainActivity, and then reduce the amount of MainActivity reference calls.