List View is a single column list that the user can scroll through. Use when you have a need to present several items on screen (like in a restaurant menu). You can control the positions of these child views by assigning the layout_gravity attribute to each child. The layout itself will be as big as its biggest child view (visible or not), plus some padding.Īvoid having several child views inside a FrameLayout since it will be difficult to avoid the child views from overlapping one another. This layout is used only to hold a single child view, thus blocking any other view in the layout. Notice the constraints on the TextView Frame Similar to RelativeLayout, this layout also requires two Measure passes. This gives you the ability to construct complex layouts with a flat view hierarchy (no nested ViewGroups). You define various constraints for every child view relative to other views present. layout_centerInParent centers the TextView ConstraintĪ constraint is a connection or an alignment to the element the constraint is tied to. One useful feature of a RelativeLayout is the ability to center a child view by using the centerInParent attribute. ![]() At the same time, however, each Relative Layout has to undergo a process of two Measure passes, which can impact performance. This can keep your layout hierarchy flat with no nested view groups. Īs the name implies, this layout will set its inner child views in relative position. To do this, we can use the layout_weight attribute. Let’s say you wanted the first TextView, containing the word Hello, to always take up 3/4 of the screen’s width. It is useful when you want your layout to be consistent among devices and orientations. This is used to tell Linear Layout how to divide the space between child views. One interesting feature a Linear Layout has is the layout_weight attribute. You can specify the direction by using the android:orientation attribute. Meaning, the views will either be all in one row or one column. Organizes its children in a row with an orientation of vertical or horizontal. Keeping the process above in mind, you should try to keep the layout of your application as shallow as possible so as to reduce the time it takes to traverse the view hierarchy “assorted-color photo frame lot” by Markus Spiske on Unsplash Layouts Breakdown Linear In this fashion, what happens is that a parent will be drawn and its children will be drawn on top of it. Starting from the root node, which draws itself, it then tells its children to draw themselves. Here, each node will decide the final size and position of each of its children on the screen. It passes these limitations downward to its children, where each child will evaluate its own size (how big it wants to be) and take into consideration the limitations it has been given and its children’s limitations. ![]() In the first phase, each parent node figures out certain constraints its children have regarding their size. Each of these phases traverses the tree in a Depth First Search order. Once the tree is formed, there are 3 phases that will happen: Measure, Layout and Draw. This means that if you have layout B that is nested inside layout A, they will have a child - parent relationship (layout A is the parent of layout B). But how do they get converted to the objects we see on the screen? Each XML file gets instantiated (read: inflated) and a view hierarchy tree is formed. Layouts are saved as XML files in Android. A hierarchy of ViewGroup and View Measure -> Layout -> Draw -> Repeat View, on the other hand, is the basic building block of UI elements. For example, a LinearLayout is a ViewGroup since it can contain views and other layouts as well. It represents an object which is the container for other views. Think of ViewGroup as the parent class of any view and also, the base class for layouts. The question is, which one is the best?īefore we go into detailing the different layouts, we’ll first go over the view object hierarchy and Android’s drawing process. Android applications have a whole bunch of layouts to choose from when you want to design your application. Linear, Relative, Constraint, Table, Frame and so on and so forth.
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