DrawerLayout modify sensitivity?

Question

The DrawerLayout default sensitivity is okay, but I would like to make it a little easier to do the left-to-right sliding gesture on the side of the screen to open the drawerlayout. I find it particiular difficult on tablets, but also on some phones.

I don't see any gesture or gesture controller references in the DrawerLayout page on the web API.. Has anyone seen something that will allow us to do this?

Answer 1

For android.support.v4.widget.DrawerLayout I came up with a hack which allows you to expand the area where sliding gesture (stroke) can start, thus making sliding gesture easier.

Hack implementation:

    // assuming mDrawerLayout is an instance of android.support.v4.widget.DrawerLayout
    try {

        // get dragger responsible for the dragging of the left drawer
        Field draggerField = DrawerLayout.class.getDeclaredField("mLeftDragger");
        draggerField.setAccessible(true);
        ViewDragHelper vdh = (ViewDragHelper)draggerField.get(mDrawerLayout);

        // get access to the private field which defines
        // how far from the edge dragging can start
        Field edgeSizeField = ViewDragHelper.class.getDeclaredField("mEdgeSize");
        edgeSizeField.setAccessible(true);

        // increase the edge size - while x2 should be good enough,
        // try bigger values to easily see the difference
        int origEdgeSize = (int)edgeSizeField.get(vdh);
        int newEdgeSize = (int) (origEdgeSize * 2); 
        edgeSizeField.setInt(vdh, newEdgeSize);

    } catch (Exception e) {
        // we unexpectedly failed - e.g. if internal implementation of 
        // either ViewDragHelper or DrawerLayout changed
    }

Explanation:

The hack is based on the fact that DrawerLayout class relies on instances of ViewDragHelper to handle the dragging. There are two instances - one for the left drawer, and one for the right one. They are getting instantiated like this:

 public DrawerLayout(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);

    ... code omitted for brevity ..

    mLeftDragger = ViewDragHelper.create(this, TOUCH_SLOP_SENSITIVITY, mLeftCallback);
    mLeftDragger.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
    mLeftDragger.setMinVelocity(minVel);
    mLeftCallback.setDragger(mLeftDragger);

    mRightDragger = ViewDragHelper.create(this, TOUCH_SLOP_SENSITIVITY, mRightCallback);
    mRightDragger.setEdgeTrackingEnabled(ViewDragHelper.EDGE_RIGHT);
    mRightDragger.setMinVelocity(minVel);
    mRightCallback.setDragger(mRightDragger);

    ... code omitted for brevity ..
}

Both mLeftDragger and mRightDragger are private fields, and mFieldSize field in ViewDragHelper is also private. There are no public methods which would let client code to set those fields - hence the hack relies on the reflection, which is fragile towards internal implementation changes in ViewDragHelper and DrawerLayout classes.

Bonus:
A comprehensive tutorial on ViewDragHelper usage