android - Simple TextView.setText causes 40% CPU Usage

Question

Running my application causes ~40% CPU usage on my Phone:

final String position = String.format("%02d:%02d:%02d", time.getHours(), time.getMinutes(),
                time.getSeconds());
getActivity().runOnUiThread(new Runnable() {
    @Override
    public void run() {
         c.mTxtPosition.setText(position);
         ...

By commenting out the setText method the CPU Usage drops to the expected level of ~4%. The method is invoked every second and does refresh ImageViews, CustomViews ... without causing the same load excess. Besides the CPU Usage dalvik constantly reports garbage collecting of about 10-1000 objects just by calling setText().

Creating a tracefile like this:

Debug.startMethodTracing("setText");
c.mTxtPosition.setText(position);
Debug.stopMethodTracing();

traceview lists the following methods as Top 5 by their respective exclusive CPU%:

• ViewParent.invalidateChildInParent(16%)
• View.requestLayout(11%)
• ViewGroup.invalidateChild(9%)
• TextView.setText(7%)
• toplevel(6%)

Has anybody an explanation for this?

Answer 1

I noticed this myself a while ago, I think the problem is that every time you call setText, the size of the textbox can change, thus requiring the entire screen to go through relayout (expensive).

I haven't tried this myself yet, but if your textbox is simple and can be made to be a relatively fixed size, maybe try to subclass TextView and create a view that does not resize itself on setText, but rather just draws whatever it can into the existing area? That would save a lot of time.

Perhaps theres already a flag to setText that can make it do this, but I'm not aware of it, though I haven't searched closely.