本文将为您提供关于android–onNewPicture()什么时候被调用？的详细介绍，我们还将为您解释androidondraw什么时候调用的相关知识，同时，我们还将为您提供关于ActionCon

本文将为您提供关于android – onNewPicture()什么时候被调用？的详细介绍，我们还将为您解释android ondraw什么时候调用的相关知识，同时，我们还将为您提供关于ActionContextCleanUp什么时候被调用，会清除哪些属性、An Overview of the Android Architecture (Android Studio)、Android / Java：onProgressUpdate()没有被调用？、Android Activity onDestroy()并不总是被调用,如果被调用,则只执行部分代码的实用信息。

• android – onNewPicture()什么时候被调用？（android ondraw什么时候调用）
• ActionContextCleanUp什么时候被调用，会清除哪些属性
• An Overview of the Android Architecture (Android Studio)
• Android / Java：onProgressUpdate()没有被调用？
• Android Activity onDestroy()并不总是被调用,如果被调用,则只执行部分代码

android – onNewPicture()什么时候被调用？（android ondraw什么时候调用）

onNewPicture()的documentation只说：

Notify the listener that the picture
has changed

我的问题是：图片什么时候改变？

我注意到有些网页生成了几十个onNewPicture(),所以很明显,在WebView上渲染页面的过程中,“图片”会多次发生变化.

是什么让WebView图片发生变化？

我没有看到任何生成少于2个onNewPicture()调用的页面页面,因此对于任何给定的HTML页面,onNewPicture()是否保证被多次调用？

解决方法:

只要已经加载的页面完成渲染(或者在某些事件使WebKit引擎重新计算页面布局的情况下重新渲染),就会调用PictureListener.onNewPicture().这实际上取决于正在加载的页面：

一个简单的纯文本页面只会呈现一次.页面加载完成后,可以多次调用其他页面(特别是Javascript重页面).

在another posting中找到的@littleFluffyKitty提示：今天很多网页都会在你移动页面时经常调用它,所以要确保onNewPicture()方法中发生的事情很快.

ActionContextCleanUp什么时候被调用，会清除哪些属性

An Overview of the Android Architecture (Android Studio)

http://www.techotopia.com/index.php/An_Overview_of_the_Android_Architecture_(Android_Studio)

So far in this book, steps have been taken to set up an environment suitable for the development of Android applications using Android Studio. An initial step has also been taken into the process of application development through the creation of a simple Android Studio application project.

Before delving further into the practical matters of Android application development, however, it is important to gain an understanding of some of the more abstract concepts of both the Android SDK and Android development in general. Gaining a clear understanding of these concepts now will provide a sound foundation on which to build further knowledge.Starting with an overview of the Android architecture in this chapter, and continuing in the next few chapters of this book, the goal is to provide a detailed overview of the fundamentals of Android development.

The Android Software Stack

Android is structured in the form of a software stack comprising applications, an operating system, run-time environment, middleware, services and libraries. This architecture can, perhaps, best be represented visually as outlined in Figure 8-1. Each layer of the stack, and the corresponding elements within each layer, are tightly integrated and carefully tuned to provide the optimal application development and execution environment for mobile devices.

Figure 8-1

The remainder of this chapter will work through the different layers of the Android stack, starting at the bottom with the Linux Kernel.

The Linux Kernel

Positioned at the bottom of the Android software stack, the Linux Kernel provides a level of abstraction between the device hardware and the upper layers of the Android software stack. Based on Linux version 2.6, the kernel provides preemptive multitasking, low-level core system services such as memory, process and power management in addition to providing a network stack and device drivers for hardware such as the device display, Wi-Fi and audio.

The original Linux kernel was developed in 1991 by Linus Torvalds and was combined with a set of tools, utilities and compilers developed by Richard Stallman at the Free Software Foundation to create a full operating system referred to as GNU/Linux. Various Linux distributions have been derived from these basic underpinnings such as Ubuntu and Red Hat Enterprise Linux.

It is important to note, however, that Android only uses the Linux kernel. That said, it is worth noting that the Linux kernel was originally developed for use in traditional computers in the form of desktops and servers. In fact, Linux is now most widely deployed in mission critical enterprise server environments. It is a testament to both the power of today’s mobile devices and the efficiency and performance of the Linux kernel that we find this software at the heart of the Android software stack.

Android Runtime - ART

When an Android app is built within Android Studio it is compiled into an intermediate bytecode format (referred to as DEX format). When the application is subsequently loaded onto the device, the Android Runtime (ART) uses a process referred to as Ahead-of-Time (AOT) compilation to translate the bytecode down to the native instructions required by the device processor. This format is known as Executable and Linkable Format (ELF).

Each time the application is subsequently launched, the ELF executable version is run, resulting in faster application performance and improved battery life.

This contrasts with the Just-in-Time (JIT) compilation approach used in older Android implementations whereby the bytecode was translated within a virtual machine (VM) each time the application was launched.

Android Libraries

In addition to a set of standard Java development libraries (providing support for such general purpose tasks as string handling, networking and file manipulation), the Android development environment also includes the Android Libraries. These are a set of Java-based libraries that are specific to Android development. Examples of libraries in this category include the application framework libraries in addition to those that facilitate user interface building, graphics drawing and database access.

• android.app – Provides access to the application model and is the cornerstone of all Android applications.
• android.content – Facilitates content access, publishing and messaging between applications and application components.
• android.database – Used to access data published by content providers and includes SQLite database management classes.
• android.graphics – A low-level 2D graphics drawing API including colors, points, filters, rectangles and canvases.
• android.hardware – Presents an API providing access to hardware such as the accelerometer and light sensor.
• android.opengl – A Java interface to the OpenGL ES 3D graphics rendering API.
• android.os – Provides applications with access to standard operating system services including messages, system services and inter-process communication.
• android.media – Provides classes to enable playback of audio and video.
• android.net – A set of APIs providing access to the network stack. Includes android.net.wifi, which provides access to the device’s wireless stack.
• android.print – Includes a set of classes that enables content to be sent to configured printers from within Android applications.
• android.provider – A set of convenience classes that provide access to standard Android content provider databases such as those maintained by the calendar and contact applications.
• android.text – Used to render and manipulate text on a device display.
• android.util – A set of utility classes for performing tasks such as string and number conversion, XML handling and date and time manipulation.
• android.view – The fundamental building blocks of application user interfaces.
• android.widget - A rich collection of pre-built user interface components such as buttons, labels, list views, layout managers, radio buttons etc.
• android.webkit – A set of classes intended to allow web-browsing capabilities to be built into applications.

Having covered the Java-based libraries in the Android runtime, it is now time to turn our attention to the C/C++ based libraries contained in this layer of the Android software stack.

C/C++ Libraries

The Android runtime core libraries outlined in the preceding section are Java-based and provide the primary APIs for developers writing Android applications. It is important to note, however, that the core libraries do not actually perform much of the actual work and are, in fact, essentially Java “wrappers” around a set of C/C++ based libraries. When making calls, for example, to the android.opengl library to draw 3D graphics on the device display, the library actually ultimately makes calls to the OpenGL ES C++ library which, in turn, works with the underlying Linux kernel to perform the drawing tasks.C/C++ libraries are included to fulfill a wide and diverse range of functions including 2D and 3D graphics drawing, Secure Sockets Layer (SSL) communication, SQLite database management, audio and video playback, bitmap and vector font rendering, display subsystem and graphic layer management and an implementation of the standard C system library (libc).

In practice, the typical Android application developer will access these libraries solely through the Java based Android core library APIs. In the event that direct access to these libraries is needed, this can be achieved using the Android Native Development Kit (NDK), the purpose of which is to call the native methods of non-Java programming languages (such as C and C++) from within Java code using the Java Native Interface (JNI).

Application Framework

The Application Framework is a set of services that collectively form the environment in which Android applications run and are managed. This framework implements the concept that Android applications are constructed from reusable, interchangeable and replaceable components. This concept is taken a step further in that an application is also able to publish its capabilities along with any corresponding data so that they can be found and reused by other applications.

The Android framework includes the following key services:

• Activity Manager – Controls all aspects of the application lifecycle and activity stack.
• Content Providers – Allows applications to publish and share data with other applications.
• Resource Manager – Provides access to non-code embedded resources such as strings, color settings and user interface layouts.
• Notifications Manager – Allows applications to display alerts and notifications to the user.
• View System – An extensible set of views used to create application user interfaces.
• Package Manager – The system by which applications are able to find out information about other applications currently installed on the device.
• Telephony Manager – Provides information to the application about the telelphony services available on the device such as status and subscriber information.
• Location Manager – Provides access to the location services allowing an application to receive updates about location changes.

Applications

Located at the top of the Android software stack are the applications. These comprise both the native applications provided with the particular Android implementation (for example web browser and email applications) and the third party applications installed by the user after purchasing the device.

Summary

A good Android development knowledge foundation requires an understanding of the overall architecture of Android. Android is implemented in the form of a software stack architecture consisting of a Linux kernel, a runtime environment and corresponding libraries, an application framework and a set of applications. Applications are predominantly written in Java and compiled down to bytecode format within the Android Studio build environment. When the application is subsequently installed on a device, this bytecode is compiled down by the Android Runtime (ART) to the native format used by the CPU. The key goals of the Android architecture are performance and efficiency, both in application execution and in the implementation of reuse in application design.

Android / Java：onProgressUpdate()没有被调用？

public class DoHardWork extends AsyncTask {

    @Override
    protected Object doInBackground(Object... params) {


        publishProgress("Requesting XML data");
        this.requestData();

        publishProgress("Returning results");
        this.returnResults();

        return null;
    }



    protected void onProgressUpdate(String text) {
        super.onProgressUpdate(text);
        MainActivity.setLog(text);
    }
}

private class DoHardWork extends AsyncTask<Void,String,Long> {
    protected Long doInBackground(Void... urls) {
         publishProgress("Requesting XML data");
         this.requestData();

         publishProgress("Returning results");
         this.returnResults();

         return null;
    }

    protected void onProgressUpdate(String... progress) {
        super.onProgressUpdate(progress);
        MainActivity.setLog(progress[0]);
    }


}

Android Activity onDestroy()并不总是被调用,如果被调用,则只执行部分代码

并不总是调用onDestroy().如果被调用,则只执行部分代码.
而且大部分时间在LogCat中我只看到消息“首先调用destroy的gps状态”.这是为什么？

protected void onDestroy(){
    super.onDestroy();
    Log.d("on destroy called", "gps state on destroy called first");

    editor.putBoolean("gpsOn", false);
    Log.d("on destroy called", "gps state on destroy called second");
    editor.commit();

    Log.d("on destroy called", "gps state on destroy called third");
    stopRouteTracking();
    Log.d("on destroy called", "gps state on destroy called  fourth");      





}

解决方法:

看看这个：

Activity OnDestroy never called?

还有这个：

http://developer.android.com/reference/android/app/Activity.html#onDestroy%28%29

基本上,从来没有保证会调用onDestroy(),在某些情况下,你的应用程序等进程将被直接杀死,无论如何都会绕过方法调用.

今天的关于android – onNewPicture()什么时候被调用？和android ondraw什么时候调用的分享已经结束，谢谢您的关注，如果想了解更多关于ActionContextCleanUp什么时候被调用，会清除哪些属性、An Overview of the Android Architecture (Android Studio)、Android / Java：onProgressUpdate()没有被调用？、Android Activity onDestroy()并不总是被调用,如果被调用,则只执行部分代码的相关知识，请在本站进行查询。