Field class in android

Message Format. Field Class

Definition

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Remarks

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.

Constructors

Properties

Returns the runtime class of this Object .

(Inherited from Object) Handle

The handle to the underlying Android instance.

(Inherited from Object) JniIdentityHashCode (Inherited from Object) JniPeerMembers Name

Returns the name of this attribute.

(Inherited from AttributedCharacterIteratorAttribute) PeerReference (Inherited from Object) ThresholdClass ThresholdType

Methods

Creates and returns a copy of this object.

(Inherited from Object) Dispose() (Inherited from Object) Dispose(Boolean) (Inherited from Object) Equals(Object)

Compares this attribute with the specified object.

(Inherited from AttributedCharacterIteratorAttribute) GetHashCode()

Calculates the hash code for objects of type Attribute .

(Inherited from AttributedCharacterIteratorAttribute) JavaFinalize()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

(Inherited from Object) Notify()

Wakes up a single thread that is waiting on this object’s monitor.

(Inherited from Object) NotifyAll()

Wakes up all threads that are waiting on this object’s monitor.

(Inherited from Object) ReadResolve()

Resolves a deserialized instance to the correct constant attribute.

(Inherited from AttributedCharacterIteratorAttribute) SetHandle(IntPtr, JniHandleOwnership)

Sets the Handle property.

(Inherited from Object) ToArray () (Inherited from Object) ToString()

Returns a string representation of the object.

(Inherited from Object) UnregisterFromRuntime() (Inherited from Object) Wait()

Causes the current thread to wait until another thread invokes the java.lang.Object#notify() method or the java.lang.Object#notifyAll() method for this object.

(Inherited from Object) Wait(Int64)

Causes the current thread to wait until another thread invokes the java.lang.Object#notify() method or the java.lang.Object#notifyAll() method for this object.

(Inherited from Object) Wait(Int64, Int32)

Causes the current thread to wait until another thread invokes the java.lang.Object#notify() method or the java.lang.Object#notifyAll() method for this object.

(Inherited from Object)

Explicit Interface Implementations

IJavaPeerable.Disposed()	(Inherited from Object)
IJavaPeerable.DisposeUnlessReferenced()	(Inherited from Object)
IJavaPeerable.Finalized()	(Inherited from Object)
IJavaPeerable.JniManagedPeerState	(Inherited from Object)
IJavaPeerable.SetJniIdentityHashCode(Int32)	(Inherited from Object)
IJavaPeerable.SetJniManagedPeerState(JniManagedPeerStates)	(Inherited from Object)
IJavaPeerable.SetPeerReference(JniObjectReference)	(Inherited from Object)

Extension Methods

Performs an Android runtime-checked type conversion.

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Field class in android

In Android, EditText is a standard entry widget in android apps. It is an overlay over TextView that configures itself to be editable. EditText is a subclass of TextView with text editing operations. We often use EditText in our applications in order to provide an input or text field, especially in forms. The most simple example of EditText is Login or Sign-in form.

Text Fields in Android Studio are basically EditText:

Important Note: An EditText is simply a thin extension of a TextView. An EditText inherits all the properties of a TextView.

Table Of Contents

EditText Code:

We can create a EditText instance by declaring it inside a layout(XML file) or by instantiating it programmatically (i.e. in Java Class).

EditText code in XML:

Retrieving / Getting the Value From EditText In Java Class:

Below is the example code of EditText in which we retrieve the value from a EditText in Java class. We have used this code in the example you will find at the end of this post.

Attributes of EditText:

Now let’s we discuss few attributes that helps us to configure a EditText in your xml.

1. id: id is an attribute used to uniquely identify a text EditText. Below is the example code in which we set the id of a edit text.

2. gravity: The gravity attribute is an optional attribute which is used to control the alignment of the text like left, right, center, top, bottom, center_vertical, center_horizontal etc.

Below is the example code with explanation included in which we set the right gravity for text of a EditText.

3. text: text attribute is used to set the text in a EditText. We can set the text in xml as well as in the java class.

Below is the example code in which we set the text “Username” in a edit text.

Setting text in EditText In Java class:

Below is the example code in which we set the text in a text view programmatically means in java class.

4. hint: hint is an attribute used to set the hint i.e. what you want user to enter in this edit text. Whenever user start to type in edit text the hint will automatically disappear.

Below is the example code with explanation in which we set the hint of a edit text.

Setting hint in EditText In Java class:

Below is the example code in which we set the text in a text view programmatically means in java class.

5. textColor: textColor attribute is used to set the text color of a text edit text. Color value is in the form of “#argb”, “#rgb”, “#rrggbb”, or “#aarrggbb”.

Below is the example code with explanation included in which we set the red color for the displayed text of a edit text.

Setting textColor in EditText In Java class:

Below is the example code in which we set the text color of a edit text programmatically means in java class.

6. textColorHint: textColorHint is an attribute used to set the color of displayed hint.

Below is the example code with explanation included in which we set the green color for displayed hint of a edit text.

Setting textColorHint in EditText In Java class:

Below is the example code in which we set the hint color of a edit text programmatically means in java class.

7. textSize: textSize attribute is used to set the size of text of a edit text. We can set the text size in sp(scale independent pixel) or dp(density pixel).

Below is the example code in which we set the 25sp size for the text of a edit text.

Setting textSize in EditText in Java class:

Below is the example code in which we set the text size of a edit text programmatically means in java class.

8. textStyle: textStyle attribute is used to set the text style of a edit text. The possible text styles are bold, italic and normal. If we need to use two or more styles for a edit text then “|” operator is used for that.

Below is the example code with explanation included, in which we set the bold and italic text styles for text.

9. background: background attribute is used to set the background of a edit text. We can set a color or a drawable in the background of a edit text.

Below is the example code with explanation included in which we set the black color for the background, white color for the displayed hint and set 10dp padding from all the side’s for edit text.

Setting Background in EditText In Java class:

Below is the example code in which we set the background color of a edit text programmatically means in java class.

10. padding: padding attribute is used to set the padding from left, right, top or bottom. In above example code of background we also set the 10dp padding from all the side’s of edit text.

Example I – EditText in Android Studio

Below is the example of edit text in which we get the value from multiple edittexts and on button click event the Toast will show the data defined in Edittext.

Step 1: Create a new project in Android Studio and name it EditTextExample.
Step 2: Now Open res -> layout -> xml (or) activity_main.xml and add following code. In this code we have added multiple edittext and a button with onclick functionality.

Step 3: Now open app -> java -> package -> MainActivity.java and add the below code.
In this we just fetch the text from the edittext, further with the button click event a toast will show the text fetched before.

Output:

Now start the AVD in Emulator and run the App. You will see screen asking you to fill the data in required fields like name, password(numeric), email, date, contact number. Enter data and click on button. You will see the data entered will be displayed as Toast on screen.

Example II – EditText in Android Studio

Below is the example of edit text in which we get the value from a edit text on button click event and then display it in a Toast. Below is the final output and code.

Step 1: Create a new project in Android Studio and name it EditTextExample.

Step 2: Now Open res -> layout -> xml (or) activity_main.xml and add following code. Here we will design one EditText for filling name and one Button which will be used to display the name entered by the user.

Step 3: Now open app -> java -> package -> MainActivity.java and add the below code. The explanation is included in the code itself as comment.

Output:

Now start the AVD in Emulator and run the App. You will see screen asking you to fill your name. Enter your name and click on button. You will see the name entered will be displayed as Toast on screen.

TextInputLayout / Floating Labels In EditText:

TextInputLayout is a new element introduced in Material Design Support library to display the floating label in EditText. Read our advance Floating Labels tutorial to learn how to use it in your App.

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Learn Java for Android Development: Inner Classes

In this tutorial, you’ll become familiar with the concept of inner classes in Java—those classes whose scope and definition are encompassed within another class. You’ll also learn about anonymous inner classes, which are used quite frequently when developing with the Android SDK.

Android applications are written in the Java, an object-oriented programming language. In this tutorial, you’ll learn about inner classes, when and why to use them and how they work. You’ll also learn how to create new objects dynamically using anonymous inner classes.

What You’ll Need

Technically, you don’t need any tools to complete this tutorial but you will certainly need them to develop Android applications.

To develop Android applications (or any Java applications, for that matter), you need a development environment to write and build applications. Eclipse is a very popular development environment (IDE) for Java and the preferred IDE for Android development. It’s freely available for Windows, Mac, and Linux operating systems.

For complete instructions on how to install Eclipse (including which versions are supported) and the Android SDK, see the Android developer website.

What is an Inner Class?

Most classes in Java are top-level classes. These classes, and the objects they define, are stand-alone. You can also create nested classes in order to clearly encapsulate and define subordinate objects that only matter in the context of the outer class. Nested classes are called inner classes.

Inner classes can have all the features of a regular class, but their scope is limited. Inner classes have another benefit: they have full access to the class in which they are nested—this feature makes inner classes perfect for implementing adapter functionality like iterators.

Here’s an example of a top-level class with two inner classes:

In this example, the User class has two inner classes: LoginInfo and Preferences. While all user-related data and functionality could be defined in the User class, using the inner classes to compartmentalize functionality can make code easier to read and maintain. The inner classes LoginInfo and Preferences also have access to the protected/private fields and methods available within the User class, which they might not otherwise have due to security, if they were defined as stand-alone classes themselves.

It’s important to remember, though, that inner classes really only exist to help the developer organize code; the compiler treats inner classes just like any other class, except that the inner classes have a limited scope, and are therefore tethered to the class they are defined with. Said another way, you would not be able to use or instantiate the LoginInfo or Preferences classes except with an instance of the User class, but the inner classes could access any fields or methods available in the outer class User, as needed.

Using Static Nested Classes

One particularly use for nested classes is static nested classes. A static inner class defines behavior that is not tied to a specific object instance, but applies across all instances. For example, we could add a third nested class, this time static, to the User class to control server-related functionality:

Because it’s public, this static nested class can be instantiated using the following new statement:

The outer class does not have to be instantiated to perform this instantiation, thus the use of the class name. As such, a static nested class, unlike a non-static nested class (aka inner class) does not have access to members of the outer class—they may not even be instantiated.

The Power of Anonymous Inner Classes

Android uses anonymous inner classes to great effect. Anonymous inner classes are basically developer shorthand, allowing the developer to create, define, and use a custom object all in one “line.” You may have seen examples of the use of anonymous inner class in sample code and not even realized it.
To create an anonymous inner class, you only provide the right-hand side of the definition. Begin with the new keyword, followed by the class or interface you wish to extend or implement, followed by the class definition. This will create the class and return it as a value which you can then use to call a method.
When we use an anonymous inner class, the object created does not get assigned a name (thus the term anonymous). The side effect, of course, is that the object is used used just once. For example, it’s common to use an anonymous inner class to construct a custom version of an object as a return value. For example, here we extend the Truck class (assuming its defined elsewhere and has a field called mpg and two methods, start() and stop():

Now let’s look at practical examples of anonymous inner classes used in Android.

Using an Anonymous Inner Class to Define a Listener

Android developers often use anonymous inner classes to define specialized listeners, which register callbacks for specific behavior when an event occurs. For example, to listen for clicks on a View control, the developer must call the setOnClickListener() method, which takes a single parameter: a View.OnClickListener object.
Developers routinely use the anonymous inner class technique to create, define and use their custom View.OnClickListener, as follows:

Using an Anonymous Inner Class to Start a Thread

Let’s look at another example. It’s quite common to define a new Thread class, provide the implementation of its run() method, and start that thread, all in one go:

Using a Named Inner Class

Using anonymous inner classes for listeners in Android is so common that it is practically second nature to do so. Why, then, would you not want to use them? Let’s answer this through a hypothetical example.
Let’s say you have a screen that has 100 buttons on it (we did say hypothetical, right?). Now, let’s say each button, when pressed, does the exact same thing. In this case, we’ll just listen for clicks and Toast the text from the View object passed in (the text shown on the Button that was clicked):
Here’s pseudo code to do that:

Short and elegant, so what’s wrong with it? At each iteration, a new OnClickListener object is instantiated. Since each one is exactly the same, there is no good reason to create 100 of them. Instead, you can create a single, named, inner class, instantiate it once, then pass that to the setOnClickListener() method. For instance:

If you prefer anonymity, you can still assign an anonymous inner class to a variable and use that, like so:

The method is up to you, but keep in mind the potential memory and performance issues that instantiating a bunch of objects may have.

A Note on Nuances

This tutorial is meant to be an introductory guide to inner classes in Java. There are style considerations and nuances when using inner classes in different and creative ways. Even beyond that, you can explore further to learn more about the internal effects and marginal performance differences that can show up when you use nested classes in different ways. All of this, however, is well beyond the scope of this tutorial.

A Quick Note On Terminology

Although we have tried to be consistent with the terminology on nested and inner classes, the terminology is not always consistent from various online and offline resources. The following are a list of terms from the current Sun/Oracle documentation, which is as good as any for being authoritative on Java:

• Nested Class: a class defined inside another class
• Static Nested Class: a static class defined inside another class
• Inner class: a non-static nested class defined inside another class
• Local Inner Class: a class defined within a method
• Anonymous Inner Class: an unnamed class defined within a method

Confused? You can use the java.lang.Class methods called isLocalClass() and isAnonymous() class on instantiated classes to determine a couple of these properties. An Oracle blog entry attempts to clarify the situation a little, too, with a nice Venn diagram.

Wrapping Up

The Java programming language supports nested classes, allowing the developer great flexibility in defining objects. Inner classes can be used to organize class functionality or to define specialized behaviors that would otherwise require the developer to expose class data and functionality that really shouldn’t be exposed. Static inner classes can be used to define fields and functionality that apply across all instances of a class. Finally, anonymous inner classes provide a useful shorthand for developers who want to create, define and use a custom object all at once.

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