我正在构建一个练习和学习的应用程序，用于从互联网上下载文件。我相信我将来必须对它进行许多更改，但截至目前我无法正确更新进度条。当我点击按钮时，AsyncTask子类应该运行并获取文件。当从互联网上读取文件时，应该更新进度条。问题是，有时进度条似乎立即更新，立即，有时它会长时间滞后，直到再次更新所有内容。我发现使用buffer.size（）作为publishProgress（）的参数存在问题，但我不确定如何正确地执行此操作。 onPostExecute（）也需要很长时间才能运行。作为一个侧面排队我有一小段代码，我注释掉了使用rxjava更新进度条。我正在考虑尝试使用这样的东西来取代onPostExecute（）。那会是一个坏主意吗？是“正确使用rxjava？”这是我的MainActivity：
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MAIN";
private static final String startURL = "https://www.google.com";
private static final int REQUEST_CODE_EXTERNAL = 0;
private Button runButton;
private EditText urlSpecBox;
private ProgressBar progressBar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//request for permission to write to storage here
if(ContextCompat.checkSelfPermission(getApplicationContext(), Manifest.permission.WRITE_EXTERNAL_STORAGE)
!= PackageManager.PERMISSION_GRANTED){
ActivityCompat.requestPermissions(this, (new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}), REQUEST_CODE_EXTERNAL);
}
progressBar = (ProgressBar) findViewById(R.id.progroessBar);
progressBar.setMax(100);
runButton = (Button) findViewById(R.id.dwnldButton);
runButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
try{
progressBar.setVisibility(View.VISIBLE);
progressBar.setProgress(0);
new AsyncDownload(new URL(startURL), progressBar).execute();
}catch (MalformedURLException me){
Log.e(TAG, "error with url", me);
}
}
});
urlSpecBox = (EditText) findViewById(R.id.urlSpecBox);
}
}
和我的asynctask子类：
public class AsyncDownload extends AsyncTask<Void, Integer, Void>{
private static final String TAG = "AsyncDownload";
private static final String STORAGE_LOCATION = "/sdcard/"; //android directory picker is needed
private URL url;
private ProgressBar mProgessBar;
//private ArrayList<Byte> bytes = new ArrayList<>();
public AsyncDownload(URL url, ProgressBar progressBar){
mProgessBar = progressBar;
this.url = url;
}
@Override
protected void onProgressUpdate(Integer... progress){
mProgessBar.setProgress(progress[0]);
}
@Override
protected Void doInBackground(Void... params){
try{
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
ByteArrayOutputStream buffer = new ByteArrayOutputStream();
int c;
while ((c = in.read()) != -1){
buffer.write(c);
publishProgress(buffer.size());
}
Log.i(TAG, "response received");
Random rand = new Random(4L);
String temp = String.valueOf(rand.nextInt());
String finalLocation = STORAGE_LOCATION + temp;
File file = new File(finalLocation);
file.getParentFile().mkdirs();
Log.i(TAG, file.getName());
FileOutputStream fOut = new FileOutputStream(file);
fOut.write(buffer.toByteArray());
buffer.close();
fOut.flush();
fOut.close();
FileInputStream fIn = new FileInputStream(finalLocation);
String reRead = new String();
int a;
while ((a = fIn.read()) != -1){
reRead += a;
}
Log.i(TAG, "reRead" + reRead);
//this section is for automatic file naming
/*Random rand = new Random(5L);
String fileNumber = String.valueOf(rand.nextInt());
StringBuilder sb = new StringBuilder();
sb.append(fileNumber).append("download"); //definitely needs work
Log.i(TAG, sb.toString());*/
//FileOutputStream fOut = new FileOutputStream()
}catch (IOException ioe){
Log.e(TAG, "network error" + ioe.toString(), ioe);
}
/*rx.Observable.just(0) //is it correct to use rxjava this way?
.observeOn(AndroidSchedulers.mainThread())
.subscribe(
new Action1<Integer>() {
@Override
public void call(Integer integer) {
mProgessBar.setProgress(integer);
mProgessBar.setVisibility(View.VISIBLE);
}
}
);*/
return null;
}
@Override
protected void onPostExecute(Void result){ // METHOD IS NEVER CALLED
super.onPostExecute(result);
Log.i(TAG, "onPostExecute called! - Task Completed!");
mProgessBar.setProgress(0);
mProgessBar.setVisibility(View.GONE);
}
}
编辑我的代码：
int c;
int progress = 0;
int count = buffer.size();
int fileSize = connection.getContentLength();
while ((c = in.read()) != -1){
buffer.write(c);
try{
Thread.sleep(TimeUnit.MILLISECONDS.toMillis(100L));
}catch (InterruptedException ie){
Log.e(TAG, "thread interrupted", ie);
}finally {
if (count > 0){
publishProgress((int) ((progress+=count)*100/fileSize));
}
}
//publishProgress(buffer.size());
}
答案 0 :(得分：1)
你因为你在循环中公开进度而导致滞后，它会让主线程多次调用它。我们在这里有一些解决方案：
请延迟使用Thread.sleep。至少100密耳。
尝试{ 了Thread.sleep（100）; } catch（InterruptedException e）{ } finally { if（fileLength＆gt; 0）{ this.publishProgress（（int）（（progress + = count）* 100 / fileLength））; } }
与上一个百分比相比增加1％时，公共进度。
更新代码：不需要使用缓冲区
FileOutputStream fOut = new FileOutputStream(file);
FileInputStream fIn = new FileInputStream(finalLocation);
byte data[] = new byte[4096];
long progress = 0;
int count;
int fileSize = connection.getContentLength();
while ((c = in.read()) != -1){
//we should write the data before publish progress
fOut.write(data, 0, count)
try{
Thread.sleep(100);
}catch (InterruptedException ie){
Log.e(TAG, "thread interrupted", ie);
}finally {
if (fileSize > 0){
publishProgress((int) ((progress+=count)*100/fileSize));
}
}
}
或
if (fileSize > 0) {
currentProgress = ((progress += count) * 100 / fileSize);
// Publish only on increments of 1%
if (currentProgress >= previousProgress + 1) {
this.publishProgress(currentProgress);
previousProgress = currentProgress;
}
}
答案 1 :(得分：0)
在AsyncDownload类中使用它
@Override
protected void onProgressUpdate(Integer... values) {
progressBar.setProgress(values[0]);
}