大佬教程收集整理的这篇文章主要介绍了Android中使用AsyncTask实现下载文件动态更新进度条功能,大佬教程大佬觉得挺不错的,现在分享给大家,也给大家做个参考。
1. 泛型
AysncTask<Params,Progress,Result>
Params:启动任务时传入的参数,通过调用asyncTask.execute(param)方法传入。
Progress:后台任务执行的进度,若不用显示进度条,则不需要指定。
Result:后台任务结束时返回的结果。
2. 重要方法
doInBACkground(Params... params):必须重写的方法,后台任务就在这里执行,会开启一个新的线程。params为启动任务时传入的参数,参数个数不定。
onPreExecute():在主线程中调用,在后台任务开启前的操作在这里进行,例如显示一个进度条对话框。
onPostExecute(Result result):当后台任务结束后,在主线程中调用,处理doInBACkground()方法返回的结果。
onProgressupdate(Progress... values):当在doInBACkground()中调用publishProgress(Progress... values)时,返回主线程中调用,这里的参数个数也是不定的。
onCancelled():取消任务。
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3. 注意事项
(2)AsyncTask实例必须在主线程中创建;
(3)不要手动调用doInBACkground()、onPreExecute()、onPostExecute()、onProgressupdate()方法;
(4)注意防止内存泄漏,在doInBACkground()方法中若出现对Activity的强引用,可能会造成内存泄漏。
4. 下载文件动态更新进度条(未封装)
布局:
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://scheR_999_11845@as.android.com/apk/res/android" xmlns:tools="http://scheR_999_11845@as.android.com/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" style="?android:progressBarStyleHorizontal" 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";//下载文件的名称 private static final String PDF_URL = "http://clfile.imooc.com/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.id.progressBar); 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实例必须在主线程创建 DownloadAsyncTask asyncTask = new DownloadAsyncTask(); asyncTask.execute(PDF_URL); } }); } /** * 泛型: * String:传入参数为文件下载地址 * Integer:下载过程中更新ProgressBar的进度 * Boolean:是否下载成功 */ private class DownloadAsyncTask extends AsyncTask<String,Integer,Boolean> { private String mFilePath;//下载文件的保存路径 @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();//获取内容总长度 mFilePath = Environment.getExternalStorageDirectory() + File.separator + file_name; //若存在同名文件则删除 File pdfFile = new File(mFilePath); if (pdfFile.exists()) { Boolean result = pdfFile.delete(); if (!result) { return false; } } int downloadSize = 0;//已经下载的大小 byte[] bytes = new byte[1024]; int length = 0; OutputStream out = new FiLeoutputStream(mFilePath); while ((length = in.read(bytes)) != -1) { out.write(bytes,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("下载中"); mDownloadBtn.setEnabled(false); mStatus.setText("下载中"); mProgressBar.setProgress(0); } @Override protected void onPostExecute(Boolean aBoolean) { super.onPostExecute(aBoolean); mDownloadBtn.setText("下载完成"); mStatus.setText(aBoolean ? "下载完成" + mFilePath : "下载失败"); } @Override protected void onProgressupdate(Integer... values) { super.onProgressupdate(values); if (values != null && values.length > 0) { mProgressBar.setProgress(values[0]); } } } }
5. 下载文件动态更新进度条(封装)
Activity:
public class MainActivity extends Activity { private static final String file_name = "test.pdf"; private static final String PDF_URL = "http://clfile.imooc.com/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.id.progressBar); 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("下载中"); mDownloadBtn.setEnabled(false); mStatus.setText("下载中"); mProgressBar.setProgress(0); } @Override public void onsuccess(File filE) { mDownloadBtn.setText("下载完成"); mStatus.setText(String.format("下载完成:%s",file.getPath())); } @Override public void onFail(File file,String failInfo) { mDownloadBtn.setText("开始下载"); mDownloadBtn.setEnabled(true); mStatus.setText(String.format("下载失败:%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,listener); task.execute(); } private static class DownloadAsyncTask extends AsyncTask<String,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 = "存储路径下的同名文件删除失败!"; 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,length); downloadSize += length; publishProgress(downloadSize / contentLength * 100); } in.close(); out.close(); } catch (IOException E) { e.printStackTrace(); mFailInfo = e.getmessage(); return false; } return true; } @Override protected void onPreExecute() { super.onPreExecute(); if (mListener != null) { mlistener.onStart(); } } @Override protected void onPostExecute(Boolean aBoolean) { super.onPostExecute(aBoolean); if (mListener != null) { if (aBoolean) { mlistener.onsuccess(new File(mFilePath)); } else { mlistener.onFail(new File(mFilePath),mFailInfo); } } } @Override protected void onProgressupdate(Integer... values) { super.onProgressupdate(values); if (values != null && values.length > 0) { if (mListener != null) { mlistener.onProgress(values[0]); } } } } interface OnDownloadListener{ void onStart(); void onsuccess(File filE); void onFail(File file,String failInfo); void onProgress(int progress); } }
总结
以上所述是小编给大家介绍的Android中使用AsyncTask实现下载文件动态更新进度条功能,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时@L_674_42@大家的。在此也非常感谢大家对编程小技巧网站的支持!
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