Question

I have a problem on dragging multiple Views in android. I have a two circle created using a Canvas. The problem is that I can only drag one Circle and I can’t drag the other Circle. It seems that the first Circle covers the entire screen, and when I try to drag the 2nd Circle still the 1st Circle is moving.

Here is my code.

MainActivity.java

public class MainActivity extends Activity {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}}

DragSource.java

public class DragSource extends View {

private Paint viewPaint;
private float startX;
private float startY;
private float touchOffsetX;
private float touchOffsetY;
private float x = 30;
private float y = 30;
private static final float RADIUS = 30;

//needed for finding drop target:

//the constructor:
public DragSource(Context context, AttributeSet attrs) {
    super(context, attrs);

    viewPaint = new Paint();
    viewPaint.setColor(Color.RED);
    viewPaint.setAntiAlias(true);
}

public boolean onTouchEvent(MotionEvent mEvent) {

    int eventAction = mEvent.getAction();
    switch(eventAction) 
    {
    case MotionEvent.ACTION_DOWN:
        startX = x;
        startY = y;
        touchOffsetX = mEvent.getX();
        touchOffsetY = mEvent.getY();
        break;
    case MotionEvent.ACTION_UP:

        break;
    case MotionEvent.ACTION_MOVE:   
    case MotionEvent.ACTION_CANCEL:
        x = startX + mEvent.getX() - touchOffsetX;
        y = startY + mEvent.getY() - touchOffsetY;
        break;
    }
    return true;
}

public void draw(Canvas c) {
    int w = c.getWidth();
    int h = c.getHeight();


    c.drawCircle(x, y, RADIUS, viewPaint);
    this.invalidate();
}}

my activity_main.xml

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" ><com.example.trialsdrag.DragSource
android:layout_width="wrap_content"
android:layout_height="wrap_content"/><com.example.trialsdrag.DragSource
android:layout_width="wrap_content"
android:layout_height="wrap_content"/></RelativeLayout>

Answer 1

What’s happening is your views’ size is the actually the whole screen size, and in onTouchEvent, your simply changing the drawing on them (moving the circle).

What you need to do is set android:layout_height and android:layout_width for the DragSource in your main_activity.xml, and then change the layout margins dynamically in onTouchEvent using:

RelativeLayout.LayoutParams params = (LayoutParams) getLayoutParams();
params.setMargins(x+params.leftMargin, y+params.topMargin, 0, 0);
setLayoutParams(params);