It is recommended not to use the full screen width for text in case you are beyond a certain width on a device. This border is typically above wdp. Research has shown that after this width reader much move the head to much. Afterwards use resource qualifiers for the same file to define different margins for larger devices. The Android user interface design guidelines have changes over the years. The first big change for designing Android applications came with the Android 3.
The Android 5. The material design introduces depth into the layout and uses much more animations to provide feedback to the user. This page also contains several downloadable resources, e. As of Android 5. Material design is a guide for visual, motion, and interaction design. The Android platform provides a new theme, new widgets and new API for custom shadows and animations.
Material design support that views are drawn on top of other views by assigning an elevation level to them. Views define an elevation level in dp density-independent pixels. To set the elevation of a view in a layout definition, use the android:elevation attribute.
To set the elevation of a view in the code of an activity, use the View. Android draws customizable shadows based on the value of the elevation. Material design also provides improved API for animations and provides several default animations.
Android allow you to define the look and feel, for example, colors and fonts, of Android components in XML resource files. This way you can set style related attributes in one central place. If the entry in the resource file is used to style a view, it is referred to as a style. If it is used for styling an activity or application it is called a theme.
To define a style or a theme, define an entry with the style tag and define the name attribute. This entry can contains one or more items which define values for named attributes. Styles and themes support inheritance by using the parent attribute of the style tag.
This way the style inherits all settings from the parent style and can overwrite selected attributes. Android lists all standard attributes which can be styled in the R.
You can refer to individual attributes of the current Android theme via the? This notation means that you are referring to a style attribute in the currently active theme.
For example? A theme is a style applied to an entire activity or application, rather than an individual view. The technique of defining a theme is the same as defining a style. You can define the fill color for your icons. The colors can be defined via your theme and used in the definition of your drawables or views. Need an account? Click here to sign up. Download Free PDF. Muhammad Rizal. A short summary of this paper. It also demonstrates how to use existing ContentProvider and how to define new ones.
It also demonstrates the usage of the Loader framework which allows to load data asynchronously. The tutorial is based on Eclipse 4. Table of Contents 1. SQLite and Android 1. What is SQLite? SQLite in Android 2. Prerequisites for this tutorial 3. SQLite Architecture 3. Packages 3. SQLiteOpenHelper 3. SQLiteDatabase 3. Cursor 3. Tutorial: Using SQLite 4. Introduction to the project 4. Create Project 4. Database and Data Model 4.
User Interface 4. Running the apps 5. Content provider and sharing data 5. What is a content provider? Accessing a content provider 5. Own ContentProvider 5. Security and ContentProvider 5. Thread Safety 6. Overview 6. Create contacts on your emulator 6. Using the Contact Content Provider 7. Loader 7. Purpose of the Loader class 7. Using the Loader class 7. SQLite database and CursorLoader 8. Cursors and Loaders 9.
Overview 9. Project 9. Database classes 9. Create ContentProvider 9. Resources 9. Layouts 9. Activities 9. Start your application Accessing SQLite databases directly Storage location of the SQLite database Shell access to the database More on ListViews Get the Kindle edition Questions and Discussion Links and Literature Source Code Android SQLite resources Android Resources SQLite supports standard relational database features like SQL syntax, transactions and prepared statements.
In addition it requires only little memory at runtime approx. All other types must be converted into one of these fields before saving them in the database. SQLite itself does not validate if the types written to the columns are actually of the defined type, e. Using an SQLite database in Android does not require any database setup or administration.
You only have to define the SQL statements for creating and updating the database. Afterwards the database is automatically managed for you by the Android platform. Access to an SQLite database involves accessing the filesystem. This can be slow. Therefore it is recommended to perform database operations asynchronously, for example inside the AsyncTask class.
The parts of the above directory are constructed based on the following rules. DATAis the path which the Environment. Prerequisites for this tutorial The following assumes that you have already basic knowledge in Android development. Please check the Android development tutorial to learn the basics. Packages The package android. In the constructor of your subclass you call the super method of SQLiteOpenHelper, specifying the database name and the current database version.
In this class you need to override the onCreate and onUpgrade methods. This method allows you to update the database schema. Both methods receive an SQLiteDatabaseobject as parameter which represents the database. Several Android functions rely on this standard. It is best practice to create a separate class per table. This class defines static onCreate and onUpgrade methods. More specifically SQLiteDatabaseprovides the insert , update and delete methods.
The "key" represents the table column identifier and the "value" represents the content for the table record in this column. ContentValues can be used for inserts and updates of database entries. Table 1. Parameters of the query method Parameter Comment String dbName The table name to compile the query against.
String[] A list of which table columns to return. Passing "null" will return all columns. These placeholders will get replaced by the values selectionArgs from the selectionArgs array. String[] groupBy A filter declaring how to group rows, null will cause the rows to not be grouped. String[] having Filter for the groups, null means no filter. String[] orderBy Table columns which will be used to order the data, null means no ordering. If a condition is not required you can pass null, e.
If you specify placeholder values in the where clause via? Cursor A query returns a Cursorobject. A Cursor represents the result of a query and basically points to one row of the query result. This way Android can buffer the query results efficiently; as it does not have to load all data into memory. To get the number of elements of the resulting query use the getCount method. To move between individual data rows, you can use the moveToFirst and moveToNext methods.
The isAfterLast method allows to check if the end of the query result has been reached. The "columnIndex" is the number of the column you are accessing. Cursoralso provides the getColumnIndexOrThrow String method which allows to get the column index for a column name of the table. A Cursorneeds to be closed with the close method call. The base class for these layout managers is the android. ViewGroup class.
All layout manager can be configured via attributes. Children can also define attributes which may be evaluated by their parent layout. Calculating the layout and drawing the views is a resource intensive operation.
You should use the simplest layout possible to achieve good performance. For example, you should avoid nesting layout managers too deeply or avoid using complex layout managers in case a simple layout manager is sufficient. Android activities define their user interface with views widgets and fragments.
You can also mix both approaches. Defining layouts via XML layout files is the preferred way. This separates the programming logic from the layout definition. It also allows the definition of different layouts for different devices. A layout resource file is referred to as layout. A layout is assigned to an activity via the setContentView method calls, as demonstrated in the following example code.
Views can define their size. This can be done in units of measurement or via pre-defined layout values. For example, as dp. The effect of these elements is demonstrated in the following graphics. ConstraintLayout is provided by an external library. It allows you to use a flat view hierarchy and has great performance. Also the design tools support constraint layout very well. New projects should prefer the usage of constraint layout. ConstraintLayout allows you to define constraints for views.
Using the above constraints for TextView1 its left, right and top edges are aligned to their respective parent edge. By setting the width of TextView1 to 0dp the view expands to fulfill its horizontal constraints. Instead use 0dp to make the view fulfilling its constraints. There are several attributes in ConstraintLayout to define the size or position of a view.
To define an aspect ratio one dimension has to be set to 0dp match constraints. A chain groups multiple elements. FrameLayout is a layout manager which draws all child elements on top of each other. This allows to create nice visual effects. The following screenshot shows the Gmail application which uses FrameLayout to display several button on top of another layout. LinearLayout puts all its child elements into a single column or row depending on the android:orientation attribute.
Possible values for this attribute are horizontal and vertical. This value specifies how much of the extra space in the layout is allocated to the corresponding view. RelativeLayout allows positioning the widget relative to each other.
This can be used for complex layouts. RelativeLayout is a complex layout manager and should only be used if such a complex layout is required, as it performs a resource intensive calculation to layout its children. A simple usage for RelativeLayout is if you want to center a single component. GridLayout separates its drawing area into: rows, columns, and cells. You can specify how many columns the grid should have.
For each view you can specify in which row and column it should be placed and how many columns and rows it should use. If not specified, GridLayout uses defaults, e. The ScrollView or the HorizontalScrollView class is useful to make views available, even if they do not fit onto the screen. A scroll view can contain one view, e. If the child view is too large, scroll view allows scrolling the content.
Previously, you learned about layout files, which a static XML files. In this chapter you learn about other static resource files. The specific sub-folder depends on type of resource which is stored. You can also append additional qualifiers to the folder name.
These are called resource qualifiers. These qualifiers indicate that the related resources should be used for special device configurations. For example, you can specify that a layout file is only valid for a certain screen size. The following table gives an overview of the supported resources and their standard folder prefixes. Images e. Used to define strings, colors, dimensions, styles and static arrays of strings or integers via XML files.
By convention each type is stored in a separate file, e. XML files with layout descriptions are used to define the user interface for activities and fragments. Arbitrary files saved in their raw form.
You access them via an InputStream object. For example, the following values. It defines a few String constants, a String array, a color and a dimension. Every relevant resource in the res folder, gets an ID assigned by the Android build system. The Android tooling generates a R. These references are static integer values. If you add a new resource file, the corresponding reference is automatically created in a R.
Manual changes in the R. The Android system provides methods to access the corresponding resource files via these IDs. For example, to access a String with the R. This method is defined via the Context class. If a view needs to be accessed via Java or XML code, you have to give the view a unique ID via the android:id attribute. To assign a new ID to a view use the android:id attribute of the corresponding element in the layout file. It is good practice to follow this approach.
By conversion this statement creates a new ID if necessary in the R. It is possible to define IDs in one central configuration file. This file is typically called ids. This allows you to use the predefined ID in your layout file. Otherwise you get an error messages that these files have already been created. The following listing shows an example for such a file. Android also provides resources. These are called system resources. System resources are distinguished from local resources by the android namespace prefix.
For example, android. The Resources class allows to access individual resources. An instance of the Resources class can be retrieved via the getResources method of the Context class. As activities and services extend the Context class, you can directly use this method in implementations of these components.
An instance of the Resources class is also required by other Android framework classes. For example, the following code shows how to create a Bitmap file from a reference ID. In your activity and fragment code you frequently need to access the views to access and modify their properties.
In an activity you can use the findViewById id method call to search for a view in the current layout. The id is the ID attribute of the view in the layout. The usage of this method is demonstrated by the following code. It is also possible to search in a view hierarchy with the findViewById id method, as demonstrated in the following code snippet. In your XML files, for example, your layout files, you can refer to other resources via the sign.
To use an Android system resource, include the android namespace into the references, e. The res directory contains structured values which predefined semantics for the Android platform. The assets directory can be used to store any kind of data. You can access files stored in this folder based on their path.
The assets directory also allows you to have sub-folders. But it is considered good practice to use the assets directory for such data. You access this data via the AssetsManager which you can access via the getAssets method from an instance of the Context class. The AssetsManager class allows you to read a file in the assets folder as InputStream with the open method. The following code shows an example for this. Continue to use your project which you created earlier with the com.
This file is used in the generated activity class via the setContentView reference. MainActivity is not a very descriptive name. Change the class name to CreateUserActivity. Ensure the AndroidManifest. Ensure that you update the reference to the layout file in the onCreate method call in CreateUserActivity.
Remove all views, except the top level entry which is the layout manager. In the visual design mode you can remove a view by right-clicking it and by selecting the Delete entry for the context menu.
ConstraintLayout is the preferred layout manager for modern apps, but it is heavily based on the graphical layout editor. Therefore, we start with using simpler layout managers which can also be easy edited via XML.
If necessary, change the layout manager to RelativeLayout. The result layout file should look similar to the following file. Android Studio changes its templates very frequently, so your layout file might look at bit different.
For the purpose of the exercises, the layout file must not be exactly the same, as long as the result looks similar. The easiest way is to find these elements in the Palette and drag and drop them into your layout. Change the button text to Create via the android:text property in your layout file. Assign the name onClick to the android:onClick property of your Button. This defines that a public void onClick View view method is be called in the activity once the button is pressed.
This method is implemented in the next step. You see some warning messages in the editor, e. These can be ignored for small demo applications.
If you run your application and press the button your application crashes because you still need to adjust your activity. In your activity class implement the public void onClick View view method. Use the text. Start your application and ensure that the message displays the text which the text field contains. Continue to use your project which you extended before exercise.
In this exercise you add radio buttons for the gender selection. The RadioGroup part is new. Also the layout reference of the button has changed. The rest should already be there from previous exercises. RadioGroup allows you to add a RadioGroup.
This listener is notified if the selection of the radio group changes. Run your application and select the different radio button. Display your Toast and ensure the correct data user name and gender is displayed. Adjust the alpha value of the radio button which is not selected to indicate which button was selected.
You can also scan the following barcode with your Android phone to install it via the Google Play application. Add the Color and String definitions to the file as described by the following table. Remove any existing view from your layout, either directly from the XML source or via the graphical editor. Afterwards add a LinearLayout with one EditText as child. Afterwards add a RadioGroup with two radio buttons and a button to your layout.
Do this either directly in the XML file or via the graphical editor. A simple way of organizing the components is to drag and drop them onto the Component Tree view. The result should look like the following screenshots. The first one shows the component view the second one the preview.
Switch to the XML tab of your layout file and verify that the file looks similar to the following listing. The Android tools team changes the generated code from time to time, so your XML might look slightly different.
Assign the fahrenheit string attribute to the text property of the second radio button. Ensure that the checked property is set to true for the first RadioButton. As an example you can use the last line in the following XML snippet. Also change its ID to "inputValue". All your user interface components are contained in a layout.
Assign the background color to this Layout. Select Color and then select myColor in the dialog. As an example, you can use the last line in the following XML snippet. Afterwards the background should change to the whitesmoke color. It might be difficult to see the difference. Start your Android application and type in a number, select your conversion and press the button.
The result should be displayed and the other option should get selected. Android devices comes in a variety of different configurations in the sense of size, screen pixel density, language settings, etc. Android supports the automatic selection of resources fitting to the device configuration. For this, you provide different resources in pre-defined sub-folders in the res directory. The suffix name of a sub-folder defines the device configuration for which it is valid, e.
Screens of Android devices are different in terms of resolution and in terms of density of the pixels on the screen. In case of a different screen densities the same length of a user interface component consists of a different amount of pixels.
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