java - 下载管理器无法解析 getSystemService

Question

我遵循了如何制作下载 .pdf 文件的应用程序的教程。

代码如下:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_vertretungsplan);
    Button dlbutton = (Button) findViewById(R.id.buttondownload);
    dlbutton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            DownloadManager.Request request = new DownloadManager.Request(Uri.parse(myurl));
            request.setTitle("Vertretungsplan");
            request.setDescription("wird heruntergeladen");
            request.allowScanningByMediaScanner();
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            String filename = URLUtil.guessFileName(myurl,null, MimeTypeMap.getFileExtensionFromUrl(myurl));
            request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS + "Schul-App",filename);
            DownloadManager manager =(DownloadManager) this.getSystemService(Context.DOWNLOAD_SERVICE);
            manager.enqueue(request);
        }
    });

它告诉我错误:

Cannot resolve method 'getSystemService(java.lang.string)'

Answer 1

this 指的是您正在使用的对象，因为它在 View.OnClickListener 中，它指的是该对象而不是您的 Activity 类。

应该做这样的事情

final Context c = this;
dlbutton.setOnClickListener(new View.OnClickListener() {
   @Override
    public void onClick(View view) {
        //...
        DownloadManager manager =(DownloadManager) c.getSystemService(Context.DOWNLOAD_SERVICE);
        manager.enqueue(request);
    }
});