【移动应用开发技术】怎么在Android中利用Handler实现一个文件下载功能

【移动应用开发技术】怎么在Android中利用Handler实现一个文件下载功能

这篇文章给大家介绍怎么在Android中利用Handler实现一个文件下载功能，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。代码实现在AndroidManifest.xml文件中声明申请的权限，如下所示：<uses-permission

android:name="android.permission.INTERNET"

/>

<uses-permission

android:name="android.permission.READ_EXTERNAL_STORAGE"

/>

<uses-permission

android:name="android.permission.WRITE_EXTERNAL_STORAGE"

/>新建一个名为DownloadDemo的项目，activity_main.xml代码如下：<?xml

version="1.0"

encoding="utf-8"?>

<LinearLayout

xmlns:android="/apk/res/android"

xmlns:tools="/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:gravity="center_horizontal"

android:orientation="vertical"

tools:context=".MainActivity">

<Button

android:id="@+id/button"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginTop="10dp"

android:text="下载"

/>

<ProgressBar

android:id="@+id/progressBar"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_margin="10dp"

android:max="100"

android:progress="0"

/>

</LinearLayout>MainActivity.class代码如下：public

class

MainActivity

extends

AppCompatActivity

implements

View.OnClickListener

{

public

static

final

String

APP_URL

=

"/upload/connAssitantDownload/upload/MobileAssistant_1.apk";

public

static

final

int

DOWNLOAD_MESSAGE_CODE

=

100001;

private

static

final

int

DOWNLOAD_MESSAGE_FAIL_CODE

=

100002;

public

static

final

int

REQUEST_CODE

=

1;

private

Button

button;

private

ProgressBar

progressBar;

private

MyHandler

mHandler;

@Override

protected

void

onCreate(Bundle

savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

initView();

askPermission();

mHandler

=

new

MyHandler(this);

}

public

static

class

MyHandler

extends

Handler

{

final

WeakReference<MainActivity>

mWeakReference;

public

MyHandler(MainActivity

activity)

{

this.mWeakReference

=

new

WeakReference<>(activity);

}

@Override

public

void

handleMessage(Message

msg)

{

MainActivity

activity

=

mWeakReference.get();

super.handleMessage(msg);

switch

(msg.what)

{

case

DOWNLOAD_MESSAGE_CODE:

gressBar.setProgress((Integer)

msg.obj);

if

(((Integer)

msg.obj)

==

100)

{

Toast.makeText(activity,

"文件下载已完成！",

Toast.LENGTH_SHORT).show();

}

break;

case

DOWNLOAD_MESSAGE_FAIL_CODE:

Toast.makeText(activity,

"文件下载失败！",

Toast.LENGTH_SHORT).show();

break;

}

}

}

/**

*

申请权限

*/

private

void

askPermission()

{

//将所需申请的权限添加到List集合中

List<String>

permissionList

=

new

ArrayList<>();

if

(ContextCompat.checkSelfPermission(MainActivity.this,

Manifest.permission.WRITE_EXTERNAL_STORAGE)

!=

PackageManager.PERMISSION_GRANTED)

{

permissionList.add(Manifest.permission.WRITE_EXTERNAL_STORAGE);

}

//判断权限列表是否为空，若不为空，则向用户申请权限，否则则直接执行操作

if

(!permissionList.isEmpty())

{

String[]

permissions

=

permissionList.toArray(new

String[permissionList.size()]);

ActivityCompat.requestPermissions(MainActivity.this,

permissions,

REQUEST_CODE);

}

else

{

//TODO

button.setOnClickListener(this);

}

}

/**

*

用户对请求权限的dialog做出响应之后,会处理请求权限的响应

*

*

@param

requestCode

请求码

*

@param

permissions

权限的集合

*

@param

grantResults

权限授予的结果

*/

@Override

public

void

onRequestPermissionsResult(int

requestCode,

@NonNull

String[]

permissions,

@NonNull

int[]

grantResults)

{

super.onRequestPermissionsResult(requestCode,

permissions,

grantResults);

switch

(requestCode)

{

case

REQUEST_CODE:

if

(grantResults.length

>

0)

{

for

(int

result

:

grantResults)

{

if

(result

!=

PackageManager.PERMISSION_GRANTED)

{

Toast.makeText(this,

"必须同意所有权限才能使用本程序",

Toast.LENGTH_SHORT).show();

finish();

return;

}

}

//TODO

button.setOnClickListener(this);

}

else

{

Toast.makeText(this,

"权限申请失败！",

Toast.LENGTH_SHORT).show();

finish();

}

break;

default:

break;

}

}

/**

*

点击事件

*

*

@param

v

*/

@Override

public

void

onClick(View

v)

{

switch

(v.getId())

{

case

R.id.button:

new

Thread(new

Runnable()

{

@Override

public

void

run()

{

download(APP_URL);

}

}).start();

break;

}

}

/**

*

下载

*

*

@param

appUrl

*/

private

void

download(String

appUrl)

{

try

{

//实例化一个url对象

URL

url

=

new

URL(appUrl);

//获取URLConnection对象

URLConnection

urlConnection

=

url.openConnection();

//获取输入流

InputStream

inputStream

=

urlConnection.getInputStream();

//获取文件的总长度

int

contentLength

=

urlConnection.getContentLength();

//设置软件下载到手机存储的位置文件夹名称

String

downloadFolderName

=

Environment.getExternalStorageDirectory()

+

File.separator

+

"MyApp"

+

File.separator;

File

file

=

new

File(downloadFolderName);

//若文件夹不存在则进行创建

if

(!file.exists())

{

file.mkdir();

}

String

fileName

=

downloadFolderName

+

"chaixingsi.apk";

File

apkFile

=

new

File(fileName);

if

(apkFile.exists())

{

apkFile.delete();

}

int

downloadContentLength

=

0;

int

length

=

0;

byte[]

bytes

=

new

byte[1024];

OutputStream

outputStream

=

new

FileOutputStream(fileName);

while

((length

=

inputStream.read(bytes))

!=

-1)

{

outputStream.write(bytes,

0,

length);

downloadContentLength

+=

length;

/**

*

发送消息通知主线程去更新UI

*/

Message

message

=

Message.obtain();

message.obj

=

downloadContentLength

*

100

/

contentLength;

message.what

=

DOWNLOAD_MESSAGE_CODE;

mHandler.sendMessage(message);

}

inputStream.close();

output