Question

So, I’m writing a program for Android. Right now, I’m in a class called GraphicsView, which extends View and implements View.OnClickListener. I have created a button mLeft, that is supposed to move an object to the left when pressed. I am trying to get this to display on the bottom left of the screen. In my constructor for GraphicsView I have the code:

mLeft = new Button (context.getApplicationContext ());
mLeft.setId (1); // wasn't sure what else to set for an id, I only did that to see if it would fix anything
mLeft.setOnClickListener (this);

And in my onDraw I have:

mLeft.draw (canvas);

With just this code, the program runs fine, and when I go to the activity that uses GraphicsView it works totally fine, except for the face that the button doesn’t show up anywhere.

I also have this doe in my constructor, right below the setOnClickListener:

mLeft.setX (0);
mLeft.setY (mDisplay.getHeight () - 64);
mLeft.setHeight (64);
mLeft.setWidth (64);
mLeft.setBackgroundColor (80000000);
mLeft.setText ("<");

Whenever I have this code in there, and I go to that activity, the program crashes. I do have onClick in there, and other than “Button mLeft” at the top, this is all of the code I have associated with this button. Basically, it looks like the program is crashing whenever I try to call any of those methods from Button. I have tried commenting these out to there there is only one of them present in the code at a time, so I know that each of them individually could kill the program.

The LogCat says: “12-04 15:11:03.581: I/dalvikvm(2692): Could not find method android.widget.Button.setX, referenced from method edu.pacificu.cs.Views.GraphicsView.”

Thank you for your help.

Answer 1

mLeft = new Button (context.getApplicationContext ());

Don’t do that. Use new Button(context), and then only if context is an Activity. Never use getApplicationContext() unless you know exactly why you are using it.

The LogCat says: “12-04 15:11:03.581: I/dalvikvm(2692): Could not find method android.widget.Button.setX, referenced from method edu.pacificu.cs.Views.GraphicsView.”

As @Selvin points out, you appear to be running this application on Android 2.x, using a method (setX()) that does not exist on Android 2.x. setX() and setY() are mostly for animation effects (e.g., slides). The X/Y/Z position of your View is determined by its container (layout) and that container’s configuration.