In the lunar lander example, if I add the following two lines to the
top of the doDraw method, the app crashes immediately with a
NullPointerException:
<pre>
Matrix m = canvas.getMatrix();
canvas.setMatrix( null );
</pre>
Stack trace is:
<pre>
FATAL EXCEPTION: Thread-8
java.lang.NullPointerException
at android.graphics.Matrix.preConcat(Matrix.java:233)
at android.view.Surface$CompatibleCanvas.setMatrix(Surface.java:
259)
at com.example.android.lunarlander.LunarView
$LunarThread.doDraw(LunarView.java:617)
at com.example.android.lunarlander.LunarView
$LunarThread.run(LunarView.java:360)
</pre>
The canvas documentation for setMatrix states that "If the matrix
parameter is null, then the current matrix is reset to identity", so
there's no reason this should crash.
Also, if I do not call getMatrix before calling setMatrix(null), then
setMatrix(null) is successful. So it would seem that it is the
combination of the two calls that are causing a problem.
Whats going on here?
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