Download and display images of a specified URL in Android

It seems that there has been no writing technology for a long timeArticleNow, I just recently sorted out the android development that I did a while ago and recorded it here. This is a simple application-download and display images from a specified URL.

To be honest, there is nothing special about this application. The scale is very small and the technology used is also very common, but it is a good theme for hands-on. Since it is an android application, it involves some technical aspects of Android development as follows:

1. controls such as imageswitcher, imageview, gallery, dialog, processbar

2. Network Access-httpclient, httpentity, httpget, httpresponse, etc.

3. Image File Processing-bitmap, bitmapfactory, bytearrayoutputstream, etc.

4. Java-such as weakreference

5. Unit Test-activityinstrumentationtestcase2, largetest, keyevent, etc.

Because you are not prepared to save the image file to external storage, the Read and Write contents of the database and disk files are not involved in this example. Next we will first analyze the requirements based on the software engineering practices.

In fact, it is not complicated. Let's think about the basic requirements below:

1. Enter the URL

2. Download images

3. display images

To further optimize this application, we also need to do the following:

4. Good interaction interfaces-such as URL input, error handling, and Image Display

5. Performance Optimization-memory usage, network latency, etc.

Now, after the requirements are determined, we will enter the development stage. In fact, we need to further split the Demand Based on Agile development methods. However, this is not the case if you do it yourself. Based on TDD practice principles, I will first write some tests. This is because the android project created using eclipse (there are a lot of steps to build a development environment on the Internet ). You can build a test project while building the project. Assume that the project is named picshow.

After this step, we will get two picshow and picshowtest projects. AddCodeBefore that, I want to add some test code to the picshowtest project,

In the future, a class called picshow will be used to display the downloaded image. Therefore, in the setup method, write:

 
@ Overrideprotected void setup () throws exception {super. Setup (); Final picshow A = getactivity (); assertnotnull ();}
 

When you write this code, the compilation will fail, because the picshow class is not defined yet. So we can use the magic of Eclipse's quick correction function (CTRL + 1) to create a new class. Create a textbox to enter a URL and a button to process click events. In Android, you have two options to create controls. One is to generate an instance using code and the other is to use the layout file. The usual practice is to select the latter (you can write less code), and finally you need an imageview object to display the image. Now you need to add the real test code:

@ Largetest
Public VoidTestdownloadimage ()ThrowsException {
Sendkeys (keyevent. keycode_enter );
Systemclock. Sleep (5000 );
Simpleimageviewlistadapter adapter = (simpleimageviewlistadapter) Ga. getadapter ();
Imageview IV = (imageview) Adapter. getitem (0 );
Asserttrue (IV. getdrawable ()! =Null);
}
 

In Android testing, there are several annotation: @ smalltest, @ mediumtest, @ largetest. What are the differences between these annotation operations?

Feature

Small

Medium

Large

Network Access	No	Localhost only	Yes
Database	No	Yes	Yes
File System Access	No	Yes	Yes
Use external systems	No	Discouraged	Yes
Multiple Threads	No	Yes	Yes
Sleep statements	No	Yes	Yes
System Properties	No	Yes	Yes
Time limit (seconds)	60	300	900 +

It is mainly related to the test content. We need to use the @ largetest flag to access the network during the test. Next, we will write a code for downloading the image to call the Click Event of the button:

 Public Bitmap loadimagefromurl (string URL) Throws Exception {
 Final Defaulthttpclient client =New Defaulthttpclient ();
 Final Httpget getrequest = New Httpget (URL );

Httpresponse response = client.exe cute (getrequest );
 Int Statuscode = response. getstatusline (). getstatuscode ();
 If (Statuscode! = Httpstatus. SC _ OK ){
Log. E ("picshow", "request URL failed, error code =" + statuscode );
}

Httpentity entity = response. getentity ();
 If (Entity = Null ){
Log. E ("picshow", "httpentity is null ");
}
Inputstream is = Null ;
Bytearrayoutputstream baos = New Bytearrayoutputstream ();
 Try {
Is = entity. getcontent ();
 Byte [] Buf = New   Byte [1024];
 Int Readbytes =-1;
 While (Readbytes = is. Read (BUF ))! =-1 ){
Baos. Write (BUF, 0, readbytes );
}
} Finally {
 If (Baos! = Null ){
Baos. Close ();
}
 If (Is! = Null ){
Is. Close ();
}
}
 Byte [] Imagearray = baos. tobytearray ();
 Return Bitmapfactory. decodebytearray (
Imagearray, 0, imagearray. Length );
}

In this way, a simple image download application is ready. The complete code is here