实践案例

Android 应用下载示例 清单文件 ```xml package="com.example.myapp"> android:name=".App" android:allowBackup="true" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/Theme.MyApp"> ``` 主活动（MainActivity.j影音a） ```j视频a package com.example.myapp; import android.annotation.SuppressLint; import android.app.DownloadManager; import android.content.BroadcastReceiver; import android.content.Context; import android.content.Intent; import android.content.IntentFilter; import android.net.Uri; import android.os.Build; import android.os.Bundle; import android.os.Environment; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.Toast; import androidx.appcompat.app.AppCompatActivity; public class MainActivity extends AppCompatActivity { private EditText urlEditText; private Button downloadButton; private Button cancelButton; private long downloadId; private boolean isDownloading; @Override protected void onCreate(Bundle s多媒体edInstanceState) { super.onCreate(s影音edInstanceState); setContentView(R.layout.activity_main); urlEditText = findViewById(R.id.url_edit_text); downloadButton = findViewById(R.id.download_button); cancelButton = findViewById(R.id.cancel_button); // Register a broadcast receiver to listen for download completion IntentFilter filter = new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE); registerReceiver(downloadCompleteReceiver, filter); downloadButton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { downloadFile(urlEditText.getText().toString()); } }); cancelButton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { cancelDownload(); } }); } @Override protected void onDestroy() { super.onDestroy(); unregisterReceiver(downloadCompleteReceiver); } // Request the download of a file @SuppressLint("NewApi") private void downloadFile(String url) { if (isDownloading) { Toast.makeText(getApplicationContext(), "Download already in progress", Toast.LENGTH_SHORT).show(); return; } DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE); DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url)); // Set the destination for the downloaded file request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "my_downloaded_file.apk"); // Enqueue the download request and s多媒体e the download ID downloadId = downloadManager.enqueue(request); isDownloading = true; Toast.makeText(getApplicationContext(), "Download started", Toast.LENGTH_SHORT).show(); } // Cancel the current download if it is in progress private void cancelDownload() { if (!isDownloading) { Toast.makeText(getApplicationContext(), "No download in progress", Toast.LENGTH_SHORT).show(); return; } DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE); downloadManager.remove(downloadId); isDownloading = false; Toast.makeText(getApplicationContext(), "Download cancelled", Toast.LENGTH_SHORT).show(); } // Broadcast receiver to listen for download completion private BroadcastReceiver downloadCompleteReceiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { if (intent.getAction().equals(DownloadManager.ACTION_DOWNLOAD_COMPLETE)) { long id = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1); if (id == downloadId) { isDownloading = false; // Get the downloaded file path DownloadManager downloadManager = (DownloadManager) context.getSystemService(DOWNLOAD_SERVICE); Uri downloadedFileUri = downloadManager.getUriForDownloadedFile(downloadId); // Open the downloaded file in an appropriate app Intent openFileIntent = new Intent(Intent.ACTION_VIEW); openFileIntent.setDataAndType(downloadedFileUri, "application/vnd.android.package-archive"); openFileIntent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION); startActivity(openFileIntent); } } } }; } ``` 使用指南 在 `AndroidManifest.xml` 中添加必要的权限和配置。 在 `MainActivity` 中添加一个 `EditText` 控件用于获取要下载的文件的 URL，以及两个按钮用于启动和取消下载。 4. 实现 `downloadFile()` 方法以请求文件下载。 5. 实现 `cancelDownload()` 方法以取消正在进行的下载。 运行 导入项目并运行它。 输入要下载的文件的 URL。 单击“下载”按钮开始下载。 4. 单击“取消”按钮取消下载（可选）。