android - 为什么应用程序在超过 3g 而不是通过 WiFi 下载时崩溃？

Question

出于某种原因，每次用户在使用 3g 数据时单击下载按钮时，屏幕都会完全变黑，并且应用会请求强制关闭。

    private final String PATH = Environment.getExternalStorageDirectory() + "/folder";


    public void DownloadFromUrl(String fileName, String saveTo) {  
            try {
                    URL url = new URL("http://example.com/" + fileName + ".png");
                    File file = new File(fileName + ".png");

                    long startTime = System.currentTimeMillis();

                    URLConnection urlconnection = url.openConnection();




                    InputStream iS = urlconnection.getInputStream();
                    BufferedInputStream bis = new BufferedInputStream(iS);


                    ByteArrayBuffer baf = new ByteArrayBuffer(50);
                    int current = 0;
                    while ((current = bis.read()) != -1) {
                            baf.append((byte) current);
                    }


                    FileOutputStream fos = new FileOutputStream(PATH + saveTo);
                    fos.write(baf.toByteArray());
                    fos.close();
                    Toast t= Toast.makeText(getApplicationContext(), "Downloaded '" + saveTo + "' to '" + PATH + "'.", Toast.LENGTH_SHORT);
                    t.show();
            } catch (IOException e) {
                    Log.d("ImageManager", "Error: " + e);
            }

    }

Answer 1

因为您正在通过长时间运行的操作阻塞 UI 线程。

相反，尝试在后台线程中发出请求，Handler , Service , IntentService , AsyncTask ，或其他东西，这样 UI 线程就不会卡住。