RelativeLayout add rule "RelativeLayout.LEFT_OF" not working

android, android-layout, android-relativelayout

Solution

I think If i put an control A in the relativelayout, then i add control B and declare it's on the left of the control A, the result should be the control B will push the control A to its right, right?

Your assumption is incorrect, the control A will not be pushed to the right unless you specified this with a `RelativeLayout.LayoutParams` rule. `RelativeLayout` places its children one one top of each other starting at the top-left corner of the screen if you don't specify placement rules for them. When you add the `View` A to the `RelativeLayout` without any rules(like `layout_alignParentRight`) it will be placed starting from the top-left corner of the screen. Then, when you add the `View` B, the rule `to_leftOf` will apply to this `View` position but this rule doesn't mean anything for the `View` A who will maintain its position on the screen. This will make `View` B to be place to the left of `View` A but outside of the screen as `View` A bounds start from the left border of the screen.

The `Button` will be placed to the left of the `ListView` when you use `layout_alignParentRight="true"` because there is now space to actually see the `Button`(it's not outside anymore). `addView(View child, int index, LayoutParams params)` works in a `LinearLayout` because the `LinearLayout` arranges its children in a row or column(depending on orientation) so when you add a `View` at a specific position, it will push the other `Views` after it to the right or below(depending on orientation)(there is no relative positioning of the views in a `LinearLayout`, the only rule is that the children come one after the other).

Starting with the `ListView` without any rules set on it, here is an example on how to make the `Button` to appear on the left of the `ListView`:

RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT);
Button button2 = new Button(this);
button2.setText("I am button 2");
button2.setId(1000);
m_relativeLayout.addView(button2, layoutParams);
RelativeLayout.LayoutParams rlp = (RelativeLayout.LayoutParams) m_listView
            .getLayoutParams();
rlp.addRule(RelativeLayout.RIGHT_OF, button2.getId());

The Button will be added as normal to the screen and it will appear starting from the top-left corner of the screen. Without the two lines from the code above the `Button` and `ListView` will overlap as this is the normal behavior of `RelativeLayout` for children without any rules on them. We then explicitly modify the position of the `ListView` to move it to the right(with the last two line from the code above).

Problem

Original source