Android Using Intent application
Seemingly ordinary most strange, as hard as it is easy. Northern Song Dynasty. Wang Anshi
Actually, the most seemingly ordinary things extraordinary, simply can not do a good job; success seem very easy, and the success of the process was fraught with hardships.
For we believe that a very common thing, dismissive, would never grow in, down to earth, just from the success and step forward; success does not like to see so easy to find a shortcut is not desirable, we often than others pay more hard work and effort.
Today we are speaking about the principles and applications of the Android Intent.
Earlier we summarize a few important components of Android, I believe we have been for these components have a clear understanding, we look at a few common operations:
Start a Activity: Context.startActivity (Intent intent);
Start a Service: Context.startService (Intent service);
Binding a Service: Context.bindService (Intent service, ServiceConnection conn, int flags);
Send a Broadcast: Context.sendBroadcast (Intent intent);
We found that in these operations, there is an Intent to participate, looks like a very important component, so in the end Intent What is it?
In simple terms, Intent is for data transfer between the various components of the system's data load. When we need to make a call to action, we can tell by Intent Android system to complete this process, Intent is to call an operation notification.
Intent has several important attributes, here we will be introduced one by one:
1.action, actions to be executed
For the following statement of Activity:
TargetActivity stated in its <intent-filter> in the <action>, ie, the target action, if we need to make a jump action, you need to specify the target in the Intent of the action, as follows:
When we specify the appropriate action for the Intent, then call startActivity method, the system will jump to the corresponding Activity according to action.
In addition to the action custom, Intent also contains a number of default action, just to name a few:
Every action has its specific purpose, the following will use to them.
Additional information 2.data and extras, that is to be operated to perform data movement and delivery to destination
Here's give an example to interact with the browser:
The above two methods are the start the browser and open the specified web page, keyword search, corresponding to the action is Intent.ACTION_VIEW and Intent.ACTION_WEB_SEARCH, the former need to specify the page address, which is required to specify the key information for critical word search, the browser will follow the default search engine set up their own search.
We note that when you open the page, specify a data attribute of Intent, which is actually designated to operate the data is in the form of a URI, we can convert a specified string prefix to a specific URI types, such as: " http: "or" https: "represents the network address type," tel: "indicates the phone number type," mailto: "indicates the type of e-mail addresses, and so on. For example, we want to call a given number, you can do this:
So how do we know whether or not to accept such a target prefix it? This requires a look at the matching rules target <data /> element of the.
Target <data /> tag contains the following sub-elements, they define the url matching rules:
android: scheme matches the url prefix, in addition to the "http", "https", "tel" ..., we can define your own prefix
android: host url match the hostname portion, such as "google.com", if defined as "*" indicates that any host name
android: port to match the port url
android: path matches the url path
We change what TargetActivity Footnotes:
If you specify only action at this time is not enough, we need to set the data value, as follows:
At this time, url and TargetActivity each part of all configuration information is consistent jumps succeed, otherwise it is rejected by the system.
We android: path = "/ target" is amended as android: pathPrefix = "/ target", and to meet the above requirements.
And during the search, we use a putExtra method, the keyword is placed as a parameter Intent, we become extras (additional information), there involves a Bundle object.
Bundle and Intent has a close relationship, it is mainly responsible for the Intent to save additional parameter information, which implements the android.os.Paracelable interface internally maintains a Map property type, with key pairs used to store additional parameters. When placing additional information in our use of putExtra Intent, the method checks the default Bundle examples is not empty, if empty, then create a new Bundle instance, and then place the specific parameter information to Bundle instance. We can also create your own Bundle object, you can then specify the Bundle of Intent, as follows:
It should be noted that, after using the method set putExtras Bundle object, not a reference to the operating system, but the copy operation, and then change the data so bundle instance after you have finished setting will not affect the interior of Intent additional information. How do we get the additional information provided in the Intent of it? Corresponding is, we need to get to the Bundle instance of Intent, and then removed from the key information corresponding to:
Of course, we can also use the Intent of getIntExtra and getStringExtra method to obtain, the data sources are in the Bundle Intent instance of an object type.
Earlier we relate to the three attributes of Intent: action, data and extras. In addition, Intent also includes the following properties:
3.category, to implementation of the objectives of the action or behavior traits have classified
For example: there are usually configured in our application main interface Activity:
Activity on behalf of the target task is the application resides in the initial Activity and the list appears in the application launcher in the system.
Several common category is as follows:
Intent.CATEGORY_DEFAULT (android.intent.category.DEFAULT) default category
Intent.CATEGORY_PREFERENCE (android.intent.category.PREFERENCE) indicates that the target Activity is a preference interface;
Intent.CATEGORY_BROWSABLE (android.intent.category.BROWSABLE) specified after this category, click on the image on the page or link, the system will consider the inclusion of this objective Activity optional list for the user to choose to open a picture or a link.
When setting the category of Intent, you should use addCategory (String category) method to add categories of information specified in the Intent to match the declared goal of Activity in this category.
4.type: To perform a MIME data type of the target actions can handle Activity
For example: a picture of the target can be handled include such mimeType Activity in its statement:
When using Intent match, we can use setType (String type) or setDataAndType (Uri data, String type) to set mimeType.
5.component, package or class name of the target component
When using the component matching, generally use the following forms:
Among them, the first two are used to match the target in the same package, and the third is used to match the objectives of the other package. It should be noted that, if we specify component properties in the Intent, the system will no longer be on the action, data / type, category match.
Encircle the wood, was born Haomo; nine of the units, from the tired soil; a thousand miles begins with one step. "I"
Today in the community to see a friend asked, "how to become a top architect within six months," the netizen Road "turn off the lights to sleep, not six months ...", indeed, a dream has come faster. As a programmer, set ambitious goals are admirable, but not just to dream, to practice step by step down. Into a major event, we must start from the little things; everything suddenly starting to micro, quantitative cause a qualitative change.
We talk about today is four launchMode Activity of.
Activity launchMode play in multiple jumps during an important role, it can decide whether to create a new Activity instance, whether to reuse existing Activity instance, whether other public Activity instances where a task. Here's a brief introduction to the concept of task, task stack structure of an object having a task can manage multiple Activity, launch an application, it creates a corresponding task.
Activity There are four launchMode:
We can configure AndroidManifest.xml <activity> the android: launchMode property to more than one of the four can be.
Here we introduced one by one with an example of these four lanchMode:
standard mode is the default start-up mode, not the <activity> Configuration android: launchMode property can, of course, you can also specify a value standard.
We will be an Activity, named FirstActivity, to demonstrate what the standard startup mode. FirstActivity code is as follows:
We FirstActivity TextView interface for displaying the current sequence number Activity instance, Button used to jump to the next FirstActivity interface.
Then we click on the button several times in a row, there will be the following phenomenon:
We noted instances of FirstActivity, but the serial numbers are different, and we need to continuously press the Back button twice to return to the first FristActivity. Principle standard mode as shown below:
As shown, the system will generate a jump every time a new instance of the task FirstActivity, and put on top of the stack structure, and when we press the Back button to see the original FirstActivity instance.
This is the standard start-up mode, with or without pre-existing instance, generates a new instance.
We android specified property on the basis of the above for the <activity>: launchMode = "singleTop", the system will start mode processing in accordance with singleTop jump behavior. We repeat the above several actions, there will be the following phenomenon:
We see the results vary with the standard three sequence numbers are the same, are used to say the same FirstActivity instance; if you press the back button, the program quits immediately, indicating the current stack structure is only one instance of Activity ʱ?? Principle singleTop mode as shown below:
As shown above, when the system will first look for a jump in the stack structure to see if there is an instance of positive FirstActivity top of the stack, if there is no longer generate new, but directly. Maybe my friends have doubts, I only see the stack is only one Activity, if it is more Activity how to do, how, if not in the stack? We followed through an example to confirm what everyone's questions.
We then create a new Activity named SecondActivity, as follows:
Then the code before FirstActivity Jump to:
Yes, FirstActivity will jump to SecondActivity, SecondActivity will jump to FirstActivity. Demo results are as follows:
We see two FirstActivity serial number is different, proved to jump from SecondActivity FirstActivity generate a new FirstActivity instance. Schematic is as follows:
We see that when the jump from SecondActivity to FirstActivity, the system finds there FirstActivity instance, but not at the top of the stack, then re-generate an instance.
This is singleTop start mode, if there Activity instances corresponding right in the top of the stack, then re-use, no longer generate new instance.
In the above basis, we modify FirstActivity attributes android: launchMode = "singleTask". The results demonstrate the following:
We note that in the above process, FirstActivity serial number is unchanged, SecondActivity serial number is not the only, explanation jump from SecondActivity to FirstActivity, does not generate a new instance, but to jump from FirstActivity SecondActivity When generating a new instance. Schematic singleTask mode as shown below:
In the bottom half of the figure is to jump to the results of the stack structure SecondActivity FirstActivity after changes, we note that, SecondActivity disappeared, yes, the jump in this process, the system found FirstActivity instance exists, so longer generates new examples, but the Activity instance FirstActivity all over the stack, the stack becomes FirstActivity object to display to the foreground. Maybe my friends have questions, if you will SecondActivity also set to singleTask mode, SecondActivity instance is not uniquely it? In our example this is not possible, because every time you jump from SecondActivity to FirstActivity, SecondActivity instance when forced out of the stack, jump to the next and so on FirstActivity SecondActivity, can not find the presence of SecondActivity instance, then you must generate the new instance. But if we have ThirdActivity, let SecondActivity and ThirdActivity another jump, then SecondActivity instance can guarantee unique.
This is singleTask mode, if there are corresponding Activity instance, makes this Activity Other Activity Examples Example above all out of the stack, so this Activity instance a stack object display to the foreground.
This startup mode is rather special, because it would enable a new stack structure, Acitvity placed in the new stack structure, and ensure no other instance enters Activity.
We modified FirstActivity of launchMode = "standard", SecondActivity of launchMode = "singleInstance", as it relates to multiple stack structure, we need to show id current stack structure in each Activity, so we add the following code for each Activity:
Then we'll show you the process:
Activity instances we found that the two were placed in a different stack structure, on singleInstance principle is as follows:
We see the jump from FirstActivity to SecondActivity, re-enable a new stack frame, to place SecondActivity instance, and then press the Back key, to return to the original stack structure; the figure jumped again in the bottom half of SecondActivity Go FirstActivity, this time the system will generate an original stack structure FirstActivity instance, and then rolled back twice, attention, and did not quit, but returned to the SecondActivity, why? Because the jump from SecondActivity to FirstActivity time, our starting point into a stack structure where SecondActivity instance, this way, we need to "return" to the stack structure.
If we modify the launchMode FirstActivity value singleTop, singleTask, singleInstance any one, the process will be as shown:
singleInstance startup mode is probably the most complex a model, in order to help you understand, I give an example, if we have a share applications, which is the entrance ShareActivity Activity, Activity also calls for other applications, we put the Activity of Start mode is set to singleInstance, then call in other applications. We edit ShareActivity configurations:
So then we start the Activity in other applications:
When we open ShareActivity then press the Back button to return to the original interface when, ShareActivity exist as a separate entity, if the time we open share applications, without having to create a new instance of ShareActivity to see the results, because the system will automatically find, It exists directly. You can print in ShareActivity about it taskId, to see the effect. On this process, the principle is as follows:
Android using HTTP service
In Android, in addition to using java.net package under the API to access HTTP services, we also can change a way to complete the work. Android SDK comes with Apache's HttpClient API. Apache HttpClient is a complete HTTP client, which provides full support for the HTTP protocol, you can use the HTTP GET and POST access. Here we combine instance, tell us about the use of the HttpClient.
Http we create a project, the project structure is shown:
In this project, we do not need any of Activity, all operations are done in the unit test class HttpTest.java in.
Because the use of the unit test, so here to tell us about how to configure the Android unit testing. All configuration information is done in AndroidManifest.xml:
Then, our unit test class needs to inherit android.test.AndroidTestCase class, which itself is inherited junit.framework.TestCase, and provides getContext () method is used to get Android context, this design is very useful because many Android Context API are required to complete.
Now let's look at our test case, HttpTest.java code is as follows:
Because this file contains three test cases, one by one so I will explain.
First, note that we use when positioning server address to the IP, because there can not be localhost, the server is running on the windows, and this unit test run in the Android platform, it means that if you use localhost to access the interior Android services may not be accessed, it must use IP to location services.
We first analyze testGet test cases. We use a HttpGet, request parameters directly attached to the back URL, then perform a GET request by the HttpClient, if the response is successful, made within the response stream as input and convert it to a string, and finally determine whether the GET_SUCCESS.
testGet the corresponding server-side testing Servlet code is as follows:
Then say testPost test cases. We use a HttpPost, URL back and did not come with the parameter information, parameter information is packaged into a form set by the NameValuePair type composition, and then process the call after UrlEncodedFormEntity HttpPost of setEntity method parameter settings, and finally executed by HttpClient.
testPost test corresponding server-side code is as follows:
The above two are the basic GET requests and POST requests, arguments are text data types, to meet the needs of the ordinary, but in some situations, for example, when we use to upload files, you can not use the basic GET and POST requests request, and we want to use a multi-part POST request. Here's how to use multi-part POST operations upload a file to the server.
Since HttpClient version shipped with Android does not support multi-part POST request, so we need to use a HttpMime open source project, this component is to deal specifically with the MIME type of related operations. Because HttpMime HttpComponents is included in the project, so we need to go to the official website to download apache HttpComponents, then put them into the project to go HttpMime.jar package, as shown:
Then, we observe testUpload test, InputStreamBody processing document flow parameters we use HttpMime provided with StringBody deal with ordinary text parameters, and finally all the type parameters are added to a MultipartEntity instance, and this is set to the POST request multipartEntity parameter entities, and then perform the POST request. Servlet server code is as follows:
The service uses apache open source project FileUpload processing, so we need to jar package commons-fileupload and commons-io these two projects, the development of the service side are not familiar with friends can go online to look at the relevant information.
After the above described three different situations, we need to consider a problem in practice, we can not always create HttpClient, but should only create an HttpClient for the entire application, and use it for all HTTP traffic. In addition, it should be noted that multi-threading problems that may occur when passing through a HttpClient also issued multiple requests. For these two issues, we need to improve the look of our project:
1. Expand the system default Application, and applied in the project.
2. Use ThreadSafeClientManager HttpClient library provides to create and manage HttpClient.
Project structure improved as shown:
MyApplication which extends the system's Application, the following code:
We rewrite the onCreate () method, when the system starts to create an HttpClient; rewrite the onLowMemory () and onTerminate () method to close the connection at the end of insufficient memory, and application, free up resources. It should be noted that, when instantiated DefaultHttpClient, passing an instance from one ClientConnectionManager ThreadSafeClientConnManager created, responsible for managing the HttpClient HTTP connection.
Then, I want to let this enhanced version of "Application" effect, you need to do the following configuration in AndroidManifest.xml:
If we are not configured, the system will default to android.app.Application, we added the configuration, the system will use our com.scott.http.MyApplication, then you can call in the context of the getApplication () to get the MyApplication instances.
With the above configuration, we can apply in the event of, HttpActivity.java code is as follows:
Click the "execute" button, the execution results are as follows:
Android application package using ANT
Hello everyone, today to share with you how to use ANT Android application package.
Usually we used to use eclipse to develop Android program, it will automatically help us pack the current application. If the Navigator view, we can see the following files:
In the figure above, com package is placed in our class file, classes.dex a class file after the conversion can be run on the dalvik streamline class file, resources.ap_ is through packaged resource file, ant.apk is The final package file.
ANT to use the application package, usually through the following steps:
1. aapt command generates R.java file
2. generate the corresponding java file with the command aidl
3. Use the javac command to compile the java source files to generate class files
4. dx.bat converts class files into classes.dex file
5. Generate resource package file with the command resources.ap_ aapt
6. apkbuilder.bat packaging resources and classes.dex files, generate unsigned.apk
7. jarsinger command apk certification, generate signed.apk
In order to facilitate understanding and memory, here to a flowchart to illustrate the above processes:
Above is the whole process, here we were made to explain in detail each of its parts, to figure out each step.
We need to familiarize yourself with each step using the command:
1.aapt (Android Asset Packaging Tool) command to generate R.java file based resource file
-f Force overwrite the existing file.
-m automatically generate the appropriate package directory at the location specified -J.
-J Specifies R.java file generated directory.
-S Specifies the resource directory.
-M Specify the manifest file.
-I Introduced libraries.
Note that the location where the ant our current project root directory, so many paths to enter, if necessary, on command, the following example is the same.
2.aidl (Android Interface Definition Language) commands to generate java files based .aidl definition file
The above examples of the location for the next com / scott / ant, according to package Person.aidl files generated gen Person.java corresponding directory file, example only handle a single document, the following will describe how to handle directory multiple aidl files.
3.javac (Java Compiler) command to generate a corresponding class file based on the source file
Location -d <directory> specify where the generated class file
-bootclasspath <path> Override location of bootstrap class files
Example and not take into account the following libraries referenced class path, complex cases will later encounter.
4.dx command to convert the file into a class file .dex
The above example is to convert the class file into the bin directory classes.dex file, the output to the bin directory, we may use third-party libraries, you will see later on.
The resource file is packaged 5.aapt
-f mandatory coverage
-M Specify the Manifest file
-S Specifies the resource directory
-A Specifies Inventory
-I Redistribute library
-F Specifies the package to be generated
6.apkbuilder order, according to documents and resources.ap_ classes.dex generated as visa apk package
-rf reference directory structure of the source file
7.jarsigner command to generate above apk package visa
In the process of visa, the need to use the certificate file needs to be noted that the final release is an alias for the certificate, on how to create a certificate, see below:
Of course, the above steps can also be done using ADT provides a graphical interface in eclipse, the selected item, right-click, "Android Tools => Export Signed Application Package", then select one of the Keystore selection link "Create new keystore", then follow the prompts Fill in the information on it.
These are the commands we used to, then we ought to analyze the necessary ANT build.xml:
First we need to define a large number of variable attributes, used to indicate the use of the path, directories, etc., as follows:
Then, we carried out step by step, first, initialization:
Second is to generate R.java file:
Followed aidl generate java source files:
We specify a framework.aidl, which defines a lot of android built-in objects, then we specify aidl directory and output directory, compiled after the group designated as aidl file suffix.
Next is the source file is compiled into class files:
If you use the third-party libraries, we can configure the classpath tag.
Next it is to convert class files into classes.dex:
Like the above code, if the use of third-party libraries, can be added in the form of final arguments into account.
Then the resource file is packaged:
No visa is then packaged into the apk package:
Then is apk visa:
This completes the editing build.xml, eclipse inherited the ANT, so we can run directly in the eclipse can also call in your code.
First we need to download ANT, then configure the environment variable information, and finally we called with: