TVS Technical Blog

I defined a custom SurfaceView and included an onDraw() method.

It wasn’t getting called – a mystery.

I added a background color to its declaration in main.xml and that fixed it.

Grrr.

THere is a section in the SDK docs on designing for performance. It has lots of suggestions, and some of them run contrary to “good Java” practice. Hence, if you do good Java practice, you want to look at these.

For example, they discourage getters/setters, preferring public access between classes. This is a big Object Oriented and Java No-No. But it’s the right thing to do where you need it.

Learning to work with Android, I guess it helps to play around with all the tools before doing too much serious development.

I had been wondering where to find stack traces when my code blew out with uncaught exceptions, or failed to start.

Well, I need look no farther. One of the functions of the adb utility is just that:

adb.exe logcat

It does the trick and shows lots of other interesting traces.

And, you can write to it yourself using the Log class in the SDK.

I created an android project in eclipse that had a custom MySurfaceView object that was a subclass of SurfaceView and was declared in the layout. I refactored this project several times.

When I tried to run it, it blew up immediately.

I used adb.exe logcat to look at the logs and it was having trouble “inflating” MySurfaceView – couldn’t find the class.

After wasting lots of time, I suspected that the project wasn’t being built correctly. I created a new ASurfaceView class and put all the MySurfaceView stuff in it so it was identical except for the name. I then deleted MySurfaceView.java.

The problems was fixed.

Here is how to arrange to get a click on a view that doesn’t have an onClick() method to override.

  this.setOnClickListener(
        new OnClickListener() {
            @Override
            public void onClick(View v) {
                 _mainThread.setCenter();
            }
        }
  );

So I wanted to have an object that floated around over a fixed background. This is called a “sprite.”

Examining the documentation didn’t show the word “sprite” anywhere. However, it turns out that the Lunar Lander example included with the SDK does sprite graphics (even uses the word) to animate the landing craft.

It’s pretty simple – just draw the object on your view’s graphics object.

One of the most frustrating debug problems is when the application blows up before it gets to the first debug statement.

Here are a couple of hints:

1. Using the debugger, look at the stack trace. It may have clues in it (or it may not tell you much)
2. Examing the metadata XML files and be sure all references to Java classes are exactly right – package name spelled right, etc