使用 AsyncTask 下载图像 [英] Download images with AsyncTask
问题描述
我不确定我的代码或结构出了什么问题.我想使用 AsyncTask 下载图像并同时显示进度条.但是我尝试了几种不同的方法.它仍然失败，不知道它有什么问题.我的结构流程是
I'm not really sure what goes wrong with my code or structure. I wanted to use AsyncTask to download images and display out the progress bar at the mean time. But I tried out a few different way of doing it. It still failed and no idea what's wrong with it. My structure flow is
ContentID 是一个字符串数组，用于存储图像的内容 ID.
主要问题:它设法从url下载图像并存储到手机中，但下载的图像都是相同的图像.它应该是不同的图像，这不是我所期望的.
第二个问题:应用程序下载图片时弹出进度条，但进度条没有更新进度.它只是保持 0% 并在下载完成后关闭.
我想知道是什么导致了我提到的主要和次要问题.如果您知道我的代码有什么问题，请发表评论或回答.任何帮助将不胜感激.
I wanted to know what causes primary and secodary issue as i mentioned. Please leave a comment or answer if you might know what's wrong with my code. Any help will be appreciated.
if(isSyncSuccess){
SetConstant.IMAGE_EXIST = 1;
pDialog = new ProgressDialog(GalleryScreen.this);
pDialog.setMessage("Downloading file. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setProgress(0);
pDialog.setMax(contentId.length);
pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
pDialog.setCancelable(true);
if (contentId.length>0){
Log.i(TAG, "contentid.length:" +contentId.length);
for (int i=0;i<contentId.length;i++){
if(helper.databaseChecking(useremail, contentId[i])){
contentdownload = i;
SetConstant.CONTENT_ID = contentId[i];
String URL = SetConstant.URL_DOWNLOAD_CONTENT+contentId[i];
DownloadFile downloadFile = new DownloadFile();
downloadFile.execute(URL);
}
private class DownloadFile extends AsyncTask<String, Integer, String>{
@Override
protected String doInBackground(String... sUrl){
Bitmap bm;
InputStream in;
try{
in = new java.net.URL(sUrl[0]).openStream();
bm = BitmapFactory.decodeStream(new PatchInputStream(in));
File storage = new File(Environment.getExternalStorageDirectory() + File.separator + "/Image/");
Log.i(TAG,"storage:" +storage);
Log.i(TAG,"storage:" +storage.getAbsolutePath());
if(!storage.exists()){
storage.mkdirs();
}
String FileName = "/"+SetConstant.CONTENT_ID+".jpg";
FileOutputStream fos = new FileOutputStream(storage + FileName);
bm.compress(Bitmap.CompressFormat.JPEG, 85, fos);
String filepath = storage + FileName;
File filecheck = new File (filepath);
long fileSize = filecheck.length();
fos.flush();
fos.close();
Log.i(TAG, "bm:" +bm);
Log.i(TAG, "fos:" +fos);
Log.i(TAG, "filesize:" +fileSize);
Log.i(TAG, "filepath:" +filepath);
}
catch(IOException e1){
e1.printStackTrace();
}
return null;
}
@Override
protected void onPreExecute(){
super.onPreExecute();
pDialog.show();
}
@Override
protected void onProgressUpdate(Integer... progress){
super.onProgressUpdate(progress);
pDialog.setProgress(progress[0]);
}
protected void onPostExecute(String result){
super.onPostExecute(result);
pDialog.dismiss();
}
}
编辑
现在应用程序可以下载图像，并且进度条也能正常工作！但我遇到的另一个问题是当应用程序无法完成下载时如何返回错误消息.目前，当应用程序下载失败时，它会崩溃.我认为我不应该在 doInBackground 端运行它.但是我还能在哪里进行检查?知道如何作为错误消息返回并请求用户重试而不是使应用程序崩溃吗?
Now the application able to download images according and the progress bar is working as well! But I got another issue is how to return error message when the application failed to complete the download. Currently when the application failed to download it will crash. I believed that I should not run it inside the doInBackground side. But where else can I do the checking? Any idea how to return as an error message and request for the user to retry instead of crashing the application?
推荐答案
您在 doInBackGround(...) 期间从未调用过 onProgressUpdate.请注意，运行多个 AsyncTask 实例是一个坏主意.这是我的建议:
You never called onProgressUpdate during your doInBackGround(...). Please note that running multiple instances of AsyncTask is a bad idea. Here is what I suggest:
if(isSyncSuccess){
SetConstant.IMAGE_EXIST=1;
pDialog=new ProgressDialog(GalleryScreen.this);
pDialog.setMessage("Downloading file. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setProgress(0);
pDialog.setMax(contentId.length);
pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
pDialog.setCancelable(true);
new DownloadFile().execute();
}
private class DownloadFiles extends AsyncTask<String, Integer, String> {
@Override
protected String doInBackground(String... sUrl) {
Bitmap bm;
InputStream in;
if (contentId.length > 0) {
for (int i = 0; i < contentId.length; i++) {
if (helper.databaseChecking(useremail, contentId[i])) {
contentdownload = i;
SetConstant.CONTENT_ID = contentId[i];
String URL = SetConstant.URL_DOWNLOAD_CONTENT + contentId[i];
//YOUR INTRESTING LOOP HERE.
publishProgress(30);
//SOME INTRESTING NUMBER FOR PROGRESS UPDATE
}
}
try {
in = new java.net.URL(sUrl[0]).openStream();
bm = BitmapFactory.decodeStream(new PatchInputStream(in));
File storage = new File(Environment.getExternalStorageDirectory() + File.separator + "/Image/");
Log.i(TAG, "storage:" + storage);
Log.i(TAG, "storage:" + storage.getAbsolutePath());
if (!storage.exists()) {
storage.mkdirs();
}
String FileName = "/" + SetConstant.CONTENT_ID + ".jpg";
FileOutputStream fos = new FileOutputStream(storage + FileName);
bm.compress(Bitmap.CompressFormat.JPEG, 85, fos);
String filepath = storage + FileName;
File filecheck = new File(filepath);
long fileSize = filecheck.length();
fos.flush();
fos.close();
} catch (IOException e1) {
e1.printStackTrace();
}
return null;
}
@Override
protected void onPreExecute () {
super.onPreExecute();
pDialog.show();
}
@Override
protected void onProgressUpdate (Integer...progress){
super.onProgressUpdate(progress);
pDialog.setProgress(progress[0]);
}
protected void onPostExecute (String result){
super.onPostExecute(result);
pDialog.dismiss();
}
}
}
当然，这段代码不会运行，您需要修复范围.但是我想建议的是，您的循环应该在 doInBackGround(...) 中，对于这种情况，在给定时间您应该只有 1 个 AsyncTask 实例，并调用 onProgressUpdate().
Of course this code don't run and you need to fix the scopes. But what I am trying to suggest is that your loop should be in doInBackGround(...), you should only have 1 instance of AsyncTask at given time for this case, and call the onProgressUpdate().
这篇关于使用 AsyncTask 下载图像的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
