Reflection in java android

Using reflection in Java on Android to invoke a method

This post on the official Android Developers Blog illustrates how to develop an app that only requires an early version of the API by utilizing reflection to call new APIs if they are available. Backward compatibility for Android applications can be achieved through reflection. Additionally, a simple example of using reflection in Android can be found at http://aaarkonusurum.blogspot.com/2012/02/android-ile-reflection.html. Another example of using reflection is creating a TextView at runtime by accessing the setText() method. Reflection is a solution to achieving backward compatibility, but it is a bit slow.

Reflection in Android?

You can attempt the following code snippet, which utilizes a static nested class called AppPreferences, as a functional example.

public static void main(String[] args) < AppPreferences preferences = new AppPreferences(); for(int i=1;i catch (Exception e) < System.err.print("."); >> > 

After understanding how to use it, let me know if you require further clarification.

In case you wish to call a method along with its parameters, it is essential to specify them beforehand.

 Method method = AppPreferences.class.getMethod(func, String.class); Object result = method.invoke(a, "param"); 

Java — Calling private native method using reflection, Calling private native method using reflection. Ask Question Asked 10 years, 2 But according to android src for this class, I just call it when I do such initializations. My class extends Time, but I’m removed the native function and trying to call it exactly when it is called in Time class. – Keyhan Asghari. May 18, …

Android and reflection

The usage of a single apk file is advisable if you aim for compatibility with various Android OS versions. The official Android Developers Blog has an article that explains how to develop an app that necessitates an earlier API version and employs reflection to access new APIs if they are accessible.

Ensuring that Android applications are compatible with previous versions.

Android supports reflection.

After successfully building a prototype, it is possible to assess and identify the areas causing slowdowns through benchmarking.

To minimize repeated resolution of interfaces from the same instances, it is advisable to cache them as a one-time cost instead of doing it repeatedly.

An instance of utilizing reflection on Android is demonstrated in this straightforward example, accessible at http://aaarkonusurum.blogspot.com/2012/02/android-ile-reflection.html.

Class x = Object.class; Constructor[] constructors = x.getDeclaredConstructors(); Field[] fields = x.getDeclaredFields(); Method[] methods = x.getDeclaredMethods(); for (Constructor constructor : constructors) < //constructors >for (Field field : fields) < //fields >for (Method method : methods) < //methods >

Generating a TextView programmatically using reflection in the code-behind during runtime.

String x = TextView.class.toString().replace("class ", ""); Class cls = Class.forName(x); Class param[] = new Class[1]; param[0] = Context.class; //Context=o an ki context ==> [activity.class] Constructor ct = cls.getConstructor(param); Object paramVal[] = new Object[1]; paramVal[0] = context; Object retobj = ct.newInstance(paramVal); 

Accessing the setText() function during runtime.

Class methodParam[] = new Class[1]; methodParam[0] = java.lang.CharSequence.class; Method method = cls.getMethod("setText", methodParam); Object arglist[] = new Object[1]; arglist[0] = new String("THIS TEXTVIEW HAS BEEN CREATED ON RUN TIME"); method.invoke(retobj, arglist); 

How to Invoke Method by Name in Java Dynamically, Syntax : Class.getDeclaredMethod (“method name”, parameterType) Method name: the method we want to find by name. Parameter Type: Type of parameters the method accepts. Return Type: This method would return an object with reference to the method’s address which would then be used to invoke the …

Invoke a method in Singleton class using reflection in java

I have discovered the resolution, which appears as follows.

Object b1 = m.invoke(handler.newInstance(), new Object[] < methodParameter >); 

Java — SecurityException in Android when calling, method.invoke (getPackageManager (), app.packageName, dataObserver); It says that I don´t have the permission, but I have decleared it in my manifest W/PackageManager (62): Not granting permission android.permission.DELETE_CACHE_FILES to package …

Usage of reflection in Android a bad design?

Reflection can be sluggish, but it has improved on recent Android versions. However, the issue with reflection is that modifications to the classes used may go unnoticed by the compiler. This can be particularly problematic when accessing third-party code or internal APIs that are not intended for public use. Consequently, it is generally not recommended, especially on Android due to its impact on performance. As a best practice, it is advisable to avoid reflection whenever possible.

Reflection should be avoided whenever feasible as it is an inelegant and precarious approach that can easily break during updates and is difficult to sustain. It can also result in skipping critical validation and setup measures, leading to adverse outcomes. Although there may be instances where it is the sole option, such scenarios are uncommon and do not typically arise in standard Android development.

While it is possible to include bespoke user permissions in an Android app, I fail to see its relevance in this context. It is unlikely that the user will comprehend the concept of reflection or when it is utilized. Permissions are better suited to situations where you require the user’s consent for specific actions, such as accessing their location or making phone calls.

To minimize the risks stated earlier, it is advisable to steer clear of reflection, to some extent.

1. Understanding the appropriate time and place to incorporate reflections in Android development is beneficial.
2. The design will support it.
3. The use of reflection APIs in Android design pattern depends on the requirements and nature of the app or feature. If they are necessary, they should be utilized accordingly.

Invoke a Static Method Using Java Reflection API, Overview. In this quick tutorial, we’ll discuss how to invoke a static method in Java by using the Reflection API. We’ll cover two different scenarios: The static method is public. The static method is private. 2. An Example Class. To make the demonstration and explanation easier, let’s first create a GreetingAndBye …

Источник

Learn Java for Android Development: Reflection Basics

Shane Conder & Lauren Darcey Last updated Oct 13, 2010

In this tutorial, you’ll become familiar with the concept of Java reflection: the ability of a class or object to examine details about its own implementation programmatically.

Android applications are written in the Java, a programming language that supports reflection—the ability of an object to examine itself. In this tutorial, you’ll learn the basics of Java reflection, including how to inspect the methods and fields of a given class, check for the availability of specific methods, and other practical tasks you may need to use when developing for different versions of the Android SDK.

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.

Why Use Reflection?

Reflection gives developers the flexibility to inspect and determine API characteristics at runtime, instead of compile time. Within the security constraints imposed by Java (e.g. use of public, protected, private), you can then construct objects, access fields, and invoke methods dynamically. The Java Reflection APIs are available as part of the java.lang.reflect package, which is included within the Android SDK for developers to use.

So what does this have to do with Android development? Well, with each new version of the Android SDK, classes, interfaces, methods, etc. are added, updated, and (less frequently) removed. However, Android developers often want to target devices running different versions of Android with a simple application package. To do this, Android developers may use reflection techniques to determine, at runtime, if a specific class or method is available before trying to use it. This allows the developer to leverage new APIs where available while still supporting the older devices—all in the same application.

Inspecting Classes

Java classes are represented at runtime using the Class (java.lang.Class) class. This class provides the starting point for all reflection APIs. Within this class, you’ll find many methods for inspecting different aspects of a class, such as its fields, constructors, methods, permissions, and more. You can also use the Class method called forName() to load a non-primitive class (e.g. not int, but Integer) by name dynamically at runtime, instead of at compile time:

String sClassName = "android.app.NotificationManager";

Источник