android - NullPointerException at TextView.checkForRelayout() while setText()

Question

I am trying to implement ViewHolder pattern to improve perfomance while drawing on canvas over the map. I need to create some labels for my markers. This method is called while data processing in draw()

// now we create label view and convert it into bitmap
private Bitmap createLabelBitmap(GisLaborHistoryObject object, HistoryPoint point) {
    // create view from xml
    if (vh == null) {
        vh = new ViewHolder();
        vh.view = inflater.inflate(R.layout.map_gis_history_label, null, false);
        vh.tv = (TextView) vh.view.findViewById(R.id.gislabeltext);
    }

    // set label content
    if (vh.tv != null) {
        if (!mSingleLaborHistory) {
            String name = "";
            name = object.getDisplayName();
            if (name == null || "".equals(name))
                name = object.getPersonId();
            if (name == null || "".equals(name))
                name = object.getLaborCode();
            if (name == null)
                name = "";

            vh.tv.setText(name);
        } else
            vh.tv.setText(point.getChangeDate());
    } 
    // measure resulting view
    vh.view.measure(spec, spec);
    vh.view.layout(0, 0, vh.view.getMeasuredWidth(), vh.view.getMeasuredHeight());
    Bitmap b = Bitmap.createBitmap(vh.view.getWidth(), vh.view.getHeight(), Bitmap.Config.ARGB_8888);
    canvasToDraw.setBitmap(b);
    canvasToDraw.translate(-vh.view.getScrollX(), -vh.view.getScrollY());
    vh.view.draw(canvasToDraw);
    return b;
}

spec is

spec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);

the result is Logcat:

 04-29 17:12:34.057: E/AndroidRuntime(389): java.lang.NullPointerException
 04-29 17:12:34.057: E/AndroidRuntime(389):     at android.widget.TextView.checkForRelayout(TextView.java:5497)
 04-29 17:12:34.057: E/AndroidRuntime(389):     at android.widget.TextView.setText(TextView.java:2730)
 04-29 17:12:34.057: E/AndroidRuntime(389):     at android.widget.TextView.setText(TextView.java:2598)
 04-29 17:12:34.057: E/AndroidRuntime(389):     at android.widget.TextView.setText(TextView.java:2573)
 04-29 17:12:34.057: E/AndroidRuntime(389):     at com.xxx.android.proj.ui.map.overlays.LaborsMarkerOverlay.createLabelBitmap(LaborsMarkerOverlay.java:164)

XML layout i use

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/gislabeltext"
style="@style/labelStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:paddingLeft="2dp"
android:paddingRight="2dp" />

what can be a reason of this error?

Answer 1

After looking into android source code at line 5497 I noticed that there is a check using mLayoutParams. I looked whis case in the debug mode and it is really was null! I add line which explicitly set this params. Now everything works fine.

vh.tv = (TextView) vh.view.findViewById(R.id.gislabeltext);
vh.tv.setLayoutParams(new ViewGroup.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));

My error was that i had to set LayoutParams explicitly when inflating with ViewGroup root = null; Everything works fine until I try to reuse TextView multiply times.