If you set a background drawable for a View, then the View will draw it before calling back to its onDraw method. In other words, the easiest way to layer is to pay close attention to the order in which the Views are added to your XML file within their container. Lower down in the file means higher up in the Z-axis. In Android starting from API level 21, items in the layout file get their Z-order both from how they are ordered within the file as well as from their "elevation" with a higher elevation value meaning the item gets a higher Z order.
The value of android:elevation must be a dimension value such as 10dp. We can also use the translationZ property to provide the same effect. Read more about elevation here on the official guide. If we want to overlap two views on top of each other, we can do so using either a RelativeLayout or a FrameLayout. Suppose we have two images: a background image and a foreground image and we want to place them on top of one another.
The code for this can be achieved with a RelativeLayout such as shown below:. Note: You must be sure to call bringToFront and invalidate method on the highest-level view under your root view. See a more detailed example here. To optimize layout performance, minimize the number of instantiated layouts and especially minimize deep nested layouts whenever possible. This is why you should generally use a RelativeLayout whenever possible instead of nested LinearLayout.
A few layout tips are included below:. This is just the beginning. Refer to our profiling apps guide for more resources. Jump to Section. Edit Page Page History. Overview View Layouts are a type of View class whose primary purpose is to organize and position other view controls. ConstraintLayout ConstraintLayout is Google's new default layout system. When using ConstraintLayout, make sure to toggle the Design and Blueprint mode in toolbar in the layout editor: You may wish to walk through this Google codelab to understand how to use ConstraintLayout works.
LinearLayout In a linear layout, like the name suggests, all the elements are displayed in a single direction either horizontally or vertically and this behavior is specified in android:orientation which is an attribute of the node LinearLayout. Building via ConstraintLayout You can create linear layouts now with ConstraintLayout by constraining the sides of each element with each other.
Notice how the blueprint shows the views now show a chain icon between the views: You can also distribute the views with different styles, including spread , spread inside , or packed. Building via the old way All children of a LinearLayout are displayed sequentially based on the order they are defined within the layout.
RelativeLayout In a relative layout every element arranges itself relative to other elements or a parent element. Using Alignment to Control Width or Height A less understood aspect of RelativeLayout is how the use of alignment can determine width or height.
The measured dimensions can be obtained by calling getMeasuredWidth and getMeasuredHeight. The second pair is simply known as width and height , or sometimes drawing width and drawing height. These dimensions define the actual size of the view on screen, at drawing time and after layout.
These values may, but do not have to, be different from the measured width and height. The width and height can be obtained by calling getWidth and getHeight. To measure its dimensions, a view takes into account its padding. The padding is expressed in pixels for the left, top, right and bottom parts of the view. Padding can be used to offset the content of the view by a specific number of pixels. For instance, a left padding of 2 will push the view's content by 2 pixels to the right of the left edge.
Even though a view can define a padding, it does not provide any support for margins. However, view groups provide such a support. Refer to ViewGroup and ViewGroup. MarginLayoutParams for further information.
For more information about dimensions, see Dimension Values. Each subclass of the ViewGroup class provides a unique way to display the views you nest within it. Below are some of the more common layout types that are built into the Android platform.
Note: Although you can nest one or more layouts within another layout to achieve your UI design, you should strive to keep your layout hierarchy as shallow as possible. Your layout draws faster if it has fewer nested layouts a wide view hierarchy is better than a deep view hierarchy.
A layout that organizes its children into a single horizontal or vertical row. It creates a scrollbar if the length of the window exceeds the length of the screen.
Enables you to specify the location of child objects relative to each other child A to the left of child B or to the parent aligned to the top of the parent. When the content for your layout is dynamic or not pre-determined, you can use a layout that subclasses AdapterView to populate the layout with views at runtime.
A subclass of the AdapterView class uses an Adapter to bind data to its layout. The Adapter behaves as a middleman between the data source and the AdapterView layout—the Adapter retrieves the data from a source such as an array or a database query and converts each entry into a view that can be added into the AdapterView layout. You can populate an AdapterView such as ListView or GridView by binding the AdapterView instance to an Adapter , which retrieves data from an external source and creates a View that represents each data entry.
Android provides several subclasses of Adapter that are useful for retrieving different kinds of data and building views for an AdapterView. The two most common adapters are:. For example, if you have an array of strings you want to display in a ListView , initialize a new ArrayAdapter using a constructor to specify the layout for each string and the string array:. Then simply call setAdapter on your ListView :. To customize the appearance of each item you can override the toString method for the objects in your array.
Or, to create a view for each item that's something other than a TextView for example, if you want an ImageView for each array item , extend the ArrayAdapter class and override getView to return the type of view you want for each item. When you instantiate the SimpleCursorAdapter , pass the layout to use for each result, the Cursor containing the results, and these two arrays:. The SimpleCursorAdapter then creates a view for each row in the Cursor using the provided layout by inserting each fromColumns item into the corresponding toViews view.
If, during the course of your app's life, you change the underlying data that is read by your adapter, you should call notifyDataSetChanged. This will notify the attached view that the data has been changed and it should refresh itself.
You can respond to click events on each item in an AdapterView by implementing the AdapterView. OnItemClickListener interface. For example:. Layouts are used in the Sunflower demo app.
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Android Things. Supported hardware. We have used getText method to get the text entered in the EditText views. But getText method returns an Editable instance and therefore we have typecasted it to convert it into String for further use. This can be done by using the toString method. Note: We defined editName and editPassword as global variables, hence they can be used in any method.
So now that we have user inputted name and password values, we can easily apply any logic on this dataset like performing authentication for login etc. For now, we are just going to display this information in a textView. For that, we will be using the setText method with our TextView instance to display information in it.
This is done using the following code:. Now, whenever the submit button is clicked, onClick method of submitButton is called and the user input values are stored in the name and password variables using the getText method on EditText instances. Then, using setText method, the input values are displayed in the TextView.
Now, when you press the Reset button, the text in the TextView should be reset i. Following is the code to do so:. You just need to set text equal to "" empty , for both the EditText as well as for TextView.
Drawing begins with the root node of the layout. It is requested to measure and draw the layout tree. Drawing is handled by walking the tree and rendering each View that intersects the invalid region.
In turn, each ViewGroup is responsible for requesting each of its children to be drawn with the draw method and each View is responsible for drawing itself. Because the tree is traversed pre-order, this means that parents will be drawn before i. Note: The framework doesn't draw View objects that aren't in a valid region, and also takes care of drawing the View background for you. You can force a View to draw, by calling invalidate.
The measuring pass is implemented in measure int, int and is a top-down traversal of the View tree.
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