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So in the screen dump the layout_margin properties are supplied by the ConstraintLayout LayouParams object but the Padding property is something that the Button supports. You can see them in the Properties window in the designer: You can tell Layout properties because they are of the form layout_ name in the XML file. Properties that are required by the Layout object.Thus in the Designer and in the Properties window a control's properties are shown in two groups: This means that a control has two types of property - its own and those that it gets from LayoutParams. That is instead of defining every possible property that any Layout could want a UI component that can be placed in a layout uses the appropriate LayouParams class to "import" the properties it needs for the Layout it finds itself in.
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The control that is to be placed in side the layout creates an instance of the appropriate LayoutParams class and so varies the parameters it has access to depending on the Layout container it finds itself in. The solution to the problem actually used is that each Layout defines a nested class derived from LayoutParams, that has all of the properties it needs the control to define. The simplest but unworkable way of implementing this would be to insist that every control implemented every property used by every Layout - even the ones not currently being used. In other words the properties that a control needs to work with a Layout depend on the Layout chosen and this makes things difficult to organize. Mostly you tend to think of the properties that are relevant to a control as belonging to the control but a Layout can do its job in many ways and could need the control to have lots of very specific properties to determine how it is positioned.
ANDROID STUDIO 2.3 EMULATOR DOES NOT WORK HOW TO
In Android Studio 2.3 Grid and Table are more or less unsuported in the layout designer and you have to work directly with the properties.įor this reason, this chapter introduces the three Layouts that you can get most of the basic UI work done with - Frame, Linear and Relative - along with the ConstraintLayout that in theory can do the work of the first three.īefore looking at these alternatives and how to work with them it is worth getting to grips with the basic ideas of Layouts and the principles that are common to most Layouts. The final two, TableLayout and GridLayout, are suitable for specialized types of UI and they are not as easy to use or as well supported in Android Studio. do not use multiple layouts nested inside one another. It is claimed that ConstraintLayout based UIs are easier to construct and faster because they are "flat" i.e. In principle is can be used to create any layout that you can implement using a combination of the other layouts. The ConstraintLayout can be thought of as a development on the RelativeLayout. The ConstraintLayout was new in Android Studio 2.2 and it is currently the recommended layout to use. Of these RelativeLayout and LinearLayout are the most used, with FrameLayout coming a distant third. There are six currently supported Layouts: The default Layout used by Android Studio is the ConstraintLayout and we have looked at using it in earlier chapters - but it is not the only Layout you can use with the Designer. It is also worth getting used to the XML it generates because sometimes this is the quickest, and occasionally the only, way to make the changes that you want. When using Android Studio it makes sense to use the layout editor.
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When the Layout is asked to render itself, it renders all of the View objects it contains arranged inside the area of the display it occupies. However Layouts seem to behave in very different ways to the simple Button and this raises the question what exactly is a Layout? Layouts?Ī Layout is a container for other View-derived objects. That is a Button is a view and so are the Layout classes. If you are interested in creating custom template also see:Īll of the classes and objects that make up the Android UI are derived from the same base class - the View. Third Edition Is now available in paperback and ebook. This is especially important if you want to support a range of devices. A good understanding of what the different Layouts do for you can make the difference between an easy and a difficult UI. is what allows you to position and generally arrange other components. Choice of Layout is vital to an Android UI.