【移動(dòng)應(yīng)用開(kāi)發(fā)技術(shù)】Android中怎么利用AsyncTask實(shí)現(xiàn)下載文件動(dòng)態(tài)更新進(jìn)度條功能

Android中怎么利用AsyncTask實(shí)現(xiàn)下載文件動(dòng)態(tài)更新進(jìn)度條功能，相信很多沒(méi)有經(jīng)驗(yàn)的人對(duì)此束手無(wú)策，為此本文總結(jié)了問(wèn)題出現(xiàn)的原因和解決方法，通過(guò)這篇文章希望你能解決這個(gè)問(wèn)題。1.泛型AysncTask<Params,Progress,Result>Params：?jiǎn)?dòng)任務(wù)時(shí)傳入的參數(shù)，通過(guò)調(diào)用asyncTask.execute(param)方法傳入。Progress：后臺(tái)任務(wù)執(zhí)行的進(jìn)度，若不用顯示進(jìn)度條，則不需要指定。Result：后臺(tái)任務(wù)結(jié)束時(shí)返回的結(jié)果。2.重要方法doInBackground(Params...params)：必須重寫(xiě)的方法，后臺(tái)任務(wù)就在這里執(zhí)行，會(huì)開(kāi)啟一個(gè)新的線(xiàn)程。params為啟動(dòng)任務(wù)時(shí)傳入的參數(shù)，參數(shù)個(gè)數(shù)不定。onPreExecute()：在主線(xiàn)程中調(diào)用，在后臺(tái)任務(wù)開(kāi)啟前的操作在這里進(jìn)行，例如顯示一個(gè)進(jìn)度條對(duì)話(huà)框。onPostExecute(Resultresult)：當(dāng)后臺(tái)任務(wù)結(jié)束后，在主線(xiàn)程中調(diào)用，處理doInBackground()方法返回的結(jié)果。onProgressUpdate(Progress...values)：當(dāng)在doInBackground()中調(diào)用publishProgress(Progress...values)時(shí)，返回主線(xiàn)程中調(diào)用，這里的參數(shù)個(gè)數(shù)也是不定的。onCancelled()：取消任務(wù)。3.注意事項(xiàng)（1）execute()方法必須在主線(xiàn)程中調(diào)用；（2）AsyncTask實(shí)例必須在主線(xiàn)程中創(chuàng)建；（3）不要手動(dòng)調(diào)用doInBackground()、onPreExecute()、onPostExecute()、onProgressUpdate()方法；（4）注意防止內(nèi)存泄漏，在doInBackground()方法中若出現(xiàn)對(duì)Activity的強(qiáng)引用，可能會(huì)造成內(nèi)存泄漏。4.下載文件動(dòng)態(tài)更新進(jìn)度條（未封裝）布局：<?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:orientation="vertical"

android:padding="20dp"

tools:context="com.studying.asynctaskdemo.MainActivity">

<ProgressBar

android:id="@+id/progressBar"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:progress="0"

/>

<Button

android:id="@+id/download"

android:layout_width="match_parent"

android:layout_height="50dp"

android:layout_marginTop="20dp"

android:text="@string/start_btn"

/>

<TextView

android:id="@+id/status"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginTop="20dp"

android:text="@string/waiting"

/>

</LinearLayout>Activity：public

class

MainActivity

extends

Activity

{

private

static

final

String

FILE_NAME

=

"test.pdf";//下載文件的名稱(chēng)

private

static

final

String

PDF_URL

=

"/class/assist/118/1328281/AsyncTask.pdf";

private

ProgressBar

mProgressBar;

private

Button

mDownloadBtn;

private

TextView

mStatus;

@Override

protected

void

onCreate(Bundle

savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

initView();

setListener();

}

private

void

initView()

{

mProgressBar

=

(ProgressBar)

findViewById(R.gressBar);

mDownloadBtn

=

(Button)

findViewById(R.id.download);

mStatus

=

(TextView)

findViewById(R.id.status);

}

private

void

setListener()

{

mDownloadBtn.setOnClickListener(new

View.OnClickListener()

{

@Override

public

void

onClick(View

v)

{

//AsyncTask實(shí)例必須在主線(xiàn)程創(chuàng)建

DownloadAsyncTask

asyncTask

=

new

DownloadAsyncTask();

asyncTask.execute(PDF_URL);

}

});

}

/**

*

泛型：

*

String：傳入?yún)?shù)為文件下載地址

*

Integer：下載過(guò)程中更新ProgressBar的進(jìn)度

*

Boolean：是否下載成功

*/

private

class

DownloadAsyncTask

extends

AsyncTask<String,

Integer,

Boolean>

{

private

String

mFilePath;//下載文件的保存路徑

@Override

protected

Boolean

doInBackground(String...

params)

{

if

(params

!=

null

&&

params.length

>

0)

{

String

pdfUrl

=

params[0];

try

{

URL

url

=

new

URL(pdfUrl);

URLConnection

urlConnection

=

url.openConnection();

InputStream

in

=

urlConnection.getInputStream();

int

contentLength

=

urlConnection.getContentLength();//獲取內(nèi)容總長(zhǎng)度

mFilePath

=

Environment.getExternalStorageDirectory()

+

File.separator

+

FILE_NAME;

//若存在同名文件則刪除

File

pdfFile

=

new

File(mFilePath);

if

(pdfFile.exists())

{

boolean

result

=

pdfFile.delete();

if

(!result)

{

return

false;

}

}

int

downloadSize

=

0;//已經(jīng)下載的大小

byte[]

bytes

=

new

byte[1024];

int

length

=

0;

OutputStream

out

=

new

FileOutputStream(mFilePath);

while

((length

=

in.read(bytes))

!=

-1)

{

out.write(bytes,

0,

length);

downloadSize

+=

length;

publishProgress(downloadSize

/

contentLength

*

100);

}

in.close();

out.close();

}

catch

(IOException

e)

{

e.printStackTrace();

return

false;

}

}

else

{

return

false;

}

return

true;

}

@Override

protected

void

onPreExecute()

{

super.onPreExecute();

mDownloadBtn.setText("下載中");

mDownloadBtn.setEnabled(false);

mStatus.setText("下載中");

mProgressBar.setProgress(0);

}

@Override

protected

void

onPostExecute(Boolean

aBoolean)

{

super.onPostExecute(aBoolean);

mDownloadBtn.setText("下載完成");

mStatus.setText(aBoolean

?

"下載完成"

+

mFilePath

:

"下載失敗");

}

@Override

protected

void

onProgressUpdate(Integer...

values)

{

super.onProgressUpdate(values);

if

(values

!=

null

&&

values.length

>

0)

{

mProgressBar.setProgress(values[0]);

}

}

}

}5.下載文件動(dòng)態(tài)更新進(jìn)度條（封裝）Activity：public

class

MainActivity

extends

Activity

{

private

static

final

String

FILE_NAME

=

"test.pdf";

private

static

final

String

PDF_URL

=

"/class/assist/118/1328281/AsyncTask.pdf";

private

ProgressBar

mProgressBar;

private

Button

mDownloadBtn;

private

TextView

mStatus;

@Override

protected

void

onCreate(Bundle

savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

initView();

setListener();

}

private

void

initView()

{

mProgressBar

=

(ProgressBar)

findViewById(R.gressBar);

mDownloadBtn

=

(Button)

findViewById(R.id.download);

mStatus

=

(TextView)

findViewById(R.id.status);

}

private

void

setListener()

{

mDownloadBtn.setOnClickListener(new

View.OnClickListener()

{

@Override

public

void

onClick(View

v)

{

String

localPath

=

Environment.getExternalStorageDirectory()

+

File.separator

+

FILE_NAME;

DownloadHelper.download(PDF_URL,

localPath,

new

DownloadHelper.OnDownloadListener()

{

@Override

public

void

onStart()

{

mDownloadBtn.setText("下載中");

mDownloadBtn.setEnabled(false);

mStatus.setText("下載中");

mProgressBar.setProgress(0);

}

@Override

public

void

onSuccess(File

file)

{

mDownloadBtn.setText("下載完成");

mStatus.setText(String.format("下載完成：%s",

file.getPath()));

}

@Override

public

void

onFail(File

file,

String

failInfo)

{

mDownloadBtn.setText("開(kāi)始下載");

mDownloadBtn.setEnabled(true);

mStatus.setText(String.format("下載失?。?s",

failInfo));

}

@Override

public

void

onProgress(int

progress)

{

mProgressBar.setProgress(progress);

}

});

}

});

}

}DownloadHelper：class

DownloadHelper

{

static

void

download(String

url,

String

localPath,

OnDownloadListener

listener)

{

DownloadAsyncTask

task

=

new

DownloadAsyncTask(url,

localPath,

listener);

task.execute();

}

private

static

class

DownloadAsyncTask

extends

AsyncTask<String,

Integer,

Boolean>

{

private

String

mFailInfo;

private

String

mUrl;

private

String

mFilePath;

private

OnDownloadListener

mListener;

DownloadAsyncTask(String

mUrl,

String

mFilePath,

OnDownloadListener

mListener)

{

this.mUrl

=

mUrl;

this.mFilePath

=

mFilePath;

this.mListener

=

mListener;

}

@Override

protected

Boolean

doInBackground(String...

params)

{

String

pdfUrl

=

mUrl;

try

{

URL

url

=

new

URL(pdfUrl);

URLConnection

urlConnection

=

url.openConnection();

InputStream

in

=

urlConnection.getInputStream();

int

contentLength

=

urlConnection.getContentLength();

File

pdfFile

=

new

File(mFilePath);

if

(pdfFile.exists())

{

boolean

result

=

pdfFile.delete();

if

(!result)

{

mFailInfo

=

"存儲(chǔ)路徑下的同名文件刪除失敗！";

return

false;

}

}

int

downloadSize

=

0;

byte[]

bytes

=

new

byte[1024];

int

length;

OutputStream

out

=

new

FileOutputStream(mFilePath);

while

((length

=

in.read(bytes))

!=

-1)

{

out.write(bytes,

0,

length);

downloadSize

+=

length;

publishProgress(downloadSize

/

contentLength

*

100);

}

in.close();

out.close();

}

catch

(IOException

e)

{

e.printStackTrace();

mFailInfo

=

e.getMessage();

r