Drawing on a view (or surface view, or anything really) within a layout

[Zhiming Shi]

I've done many tutorials (in my quest to find the answer to this question) so I'm basically familiar with how to draw basic shapes as well as bitmap images on a view using a canvas as well as on a surface view. The problem is, every tutorial I find is the same - it tells me to set content view to the view (or surface view).

mySurfaceView = new MySurfaceView(this);
        setContentView(mySurfaceView); 

But the whole point is that I want to draw on a view within a greater layout, so that my buttons, textboxes, etc are all visible next to my surface view (or other view within my main view) and still be able to draw on my view.

How do I do this?

[Steve Luke]

Probably the same(ish) way as doing as a content. A couple of things to thing about:
1) Make sure the view you intend to draw on has a predefined size. If not, it may (will likely) be shrunk to 0px wide and 0px tall.
2) You may find it easiest to position things with a RelativeLayout to avoid unwanted resizing
3a) You may find it easier to make the layout with the surface view in it, then get it out of the view using findViewById()
3b) Alternatively, you should put a placeholder FrameLayout where you want the surface view, then get the FrameLayout using findViewById() and adding your surface view to the frame

If you are having problems, show the layout, a simple version of the code, and a screenshot of the results, and details about the difference between expectations and results so we can help you with the issue.

[Zhiming Shi]

public class AndroidPaint extends Activity {
View viewMap;
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      viewMap = (View) findViewById(R.id.viewMap);
      //setContentView(new myView(this));
  }

As you can see, in the above code the tutorial says to change the content view to myView, but I want the content view to be the main layout.

public class MyView extends View{

public MyView(Context context) {
 super(context);
 // TODO Auto-generated constructor stub
}

@Override
protected void onDraw(Canvas canvas) {
          Paint myPaint = new Paint();
          myPaint.setColor(Color.GREEN);
          myPaint.setStyle(Paint.Style.STROKE);
          myPaint.setStrokeWidth(3);
          canvas.drawRect(10, 10, 100, 100, myPaint);
}
}

The problem is, once I've changed the content view to the main layout, I have no idea how to "connect" that MyView class to my View, which is called "viewMap". I just want the drawing that is happening in the myview class to happen to my view object, "viewMap".

When I figure out how to do that, I'll take your advice on the other things, Steve Luke, thanks!

[Zhiming Shi]

I've made a small breakthrough, but every time I click the button my app crashes.

public class MainActivity extends Activity implements LocationListener  {
	Button btnReset;
	View viewMap;
	Canvas canvas;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		viewMap = (View) findViewById(R.id.viewMap);
		canvas = new Canvas();
		btnReset = (Button) findViewById(R.id.btnReset);
		btnReset.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
				((MyView)viewMap).mContextVariable = true; //or false, etc
	            viewMap.invalidate();
			}
		});
	}
	protected void onPause() {
	    // TODO Auto-generated method stub
	    super.onPause();
	}

	@Override
	protected void onResume() {
	    // TODO Auto-generated method stub
	    super.onResume();
	}

}

class MyView extends View
{
    Paint textPaint;
    boolean mContextVariable;

    public MyView(Context context) 
    {
        super(context);

         textPaint = new Paint();
         textPaint.setColor(Color.BLACK);

    }

    @Override
    protected void onDraw(Canvas canvas)
    {
        if(mContextVariable)
        {
            canvas.drawLine(0, 0, canvas.getWidth(), canvas.getHeight(), textPaint);
        }
        else
        {
            //draw something else
        }
        canvas.drawText("testing", 0,0, textPaint);
    }
}

At the very least I've "connected" my View to the MyView class in a way that seems to be basically correct...I just don't know what I'm missing? How can I get it to draw on the view and not crash when the button is pressed?

[Steve Luke]

Zhiming Shi wrote:I've made a small breakthrough, but every time I click the button my app crashes.

What error message do you get in LogCat when the app crash. LogCat should have the stack trace which will pinpoint where the error occurs and why.

[Zhiming Shi]

Aigh, I'm a bit of a noob when it comes to Android programming. My app relies on GPS to function so I find it faster to just debug by installing it on my phone each time and then running it rather than using the emulator. My emulator is extremely slow and I'm not sure how to get the GPS and saving to SD card things to work properly when using the emulator. Using my phone, however, I don't know how to get the logcat information.

[Steve Luke]

First thing you need to do is enter Developer Mode (this is typically done in the Settings menu but varies by Android version and model so search to find out how to do it). then turn on USB debugging. When debugging is on, run the app from your IDE using the phone, then change to the LogCat view.

[Zhiming Shi]

This is great, I can't believe I didn't know about it!
Thanks!