本文實例為大家分享了Android實現下載文件的具體代碼，供大家參考，具體內容如下
1.實現效果
直接上圖：
2.代碼實現
在AndroidManifest.xml文件中聲明申請的權限，如下所示：
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<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" /> |
新建一個名為DownloadDemo的項目，activity_main.xml代碼如下：
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<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/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="下載" /> <ProgressBar android:id="@+id/progressBar" style="?android:attr/progressBarStyleHorizontal" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_margin="10dp" android:max="100" android:progress="0" /></LinearLayout> |
MainActivity.class代碼如下：
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public class MainActivity extends AppCompatActivity implements View.OnClickListener { public static final String APP_URL = "http://download.sj.qq.com/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: activity.progressBar.setProgress((Integer) msg.obj); if (((Integer) msg.obj) == 100) { Toast.makeText(activity, "文件下載已完成！", Toast.LENGTH_SHORT).show(); } break; case DOWNLOAD_MESSAGE_FAIL_CODE: Toast.makeText(activity, "文件下載失敗！", Toast.LENGTH_SHORT).show(); break; } } } /** * 申請權限 */ private void askPermission() { //將所需申請的權限添加到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); } //判斷權限列表是否為空，若不為空，則向用戶申請權限，否則則直接執行操作 if (!permissionList.isEmpty()) { String[] permissions = permissionList.toArray(new String[permissionList.size()]); ActivityCompat.requestPermissions(MainActivity.this, permissions, REQUEST_CODE); } else { //TODO button.setOnClickListener(this); } } /** * 用戶對請求權限的dialog做出響應之后,會處理請求權限的響應 * * @param requestCode 請求碼 * @param permissions 權限的集合 * @param grantResults 權限授予的結果 */ @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, "必須同意所有權限才能使用本程序", Toast.LENGTH_SHORT).show(); finish(); return; } } //TODO button.setOnClickListener(this); } else { Toast.makeText(this, "權限申請失敗！", Toast.LENGTH_SHORT).show(); finish(); } break; default: break; } } /** * 點擊事件 * * @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; } } /** * 下載 * * @param appUrl */ private void download(String appUrl) { try { //實例化一個url對象 URL url = new URL(appUrl); //獲取URLConnection對象 URLConnection urlConnection = url.openConnection(); //獲取輸入流 InputStream inputStream = urlConnection.getInputStream(); //獲取文件的總長度 int contentLength = urlConnection.getContentLength(); //設置軟件下載到手機存儲的位置文件夾名稱 String downloadFolderName = Environment.getExternalStorageDirectory() + File.separator + "MyApp" + File.separator; File file = new File(downloadFolderName); //若文件夾不存在則進行創建 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; /** * 發送消息通知主線程去更新UI */ Message message = Message.obtain(); message.obj = downloadContentLength * 100 / contentLength; message.what = DOWNLOAD_MESSAGE_CODE; mHandler.sendMessage(message); } inputStream.close(); outputStream.close(); } catch (MalformedURLException e) { //下載失敗的話也發送消息 notifyDownloadFailed(); e.printStackTrace(); } catch (IOException e) { notifyDownloadFailed(); e.printStackTrace(); } } /** * 通知下載失敗 */ private void notifyDownloadFailed() { Message message = Message.obtain(); message.what = DOWNLOAD_MESSAGE_FAIL_CODE; mHandler.sendMessage(message); } /** * 初始化視圖 */ private void initView() { button = findViewById(R.id.button); progressBar = findViewById(R.id.progressBar); }} |
3.快捷鍵總結
提取方法：Ctrl+Alt+M；
提取變量：Ctrl+Alt+V；
提取常量：Ctrl+Alt+C；
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持服務器之家。
原文鏈接：https://blog.csdn.net/qingjianduoyun/article/details/80628571
