Android设置视图位置 - setY vs setTop

Question

I was going to move the button's position programmatically. Button is in relative layout. I'd researched and found that we can use .setY() or .setTop() . It looks like they should work the same.

But in my case, .setTop() does not change the position at all and .setY() works only. I'm not sure what I did misunderstand but it's very weird for me.

Is there anybody who can explain setY() vs setTop() correctly? What is the difference?

This is layout.xml :

<RelativeLayout 
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <Button
       android:layout_width="match_parent"
       android:layout_height="40dp"
       android:layout_marginLeft="10dp"
       android:layout_marginRight="10dp"/>
</RelativeLayout>

Answer 1

The main difference between setY() and setTop() is that setY() sets the top offset of the view relative to the visual area , whereas setTop() sets the top offset of the view relative to its parent .

From the Android documentation .

setY()

Sets the visual y position of this view, in pixels. This is equivalent to setting the translationY property to be the difference between the y value passed in and the current top property.

setTop()

Sets the top position of this view relative to its parent.

Answer 2

You can notice that setTop() doesn't have effect unlike setY() . The reason is that a field mTop is being changed by layout() . The simplest way to see a changed mTop is to set a top margin.