我需要你的帮助，我的代码中存在致命错误。我不知道如何解决这个问题...请帮帮我:)。
我的代码
public class MainActivity extends Activity {
// button to show progress dialog
Button btnShowProgress;
// Progress Dialog
private ProgressDialog pDialog;
ImageView my_image;
// Progress dialog type (0 - for Horizontal progress bar)
public static final int progress_bar_type = 0;
// File url to download
private static String file_url = "https://example.pdf";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// show progress bar button
btnShowProgress = (Button) findViewById(R.id.btnProgressBar);
// Image view to show image after downloading
my_image = (ImageView) findViewById(R.id.my_image);
/**
* Show Progress bar click event
* */
btnShowProgress.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// starting new Async Task
new DownloadFileFromURL().execute(file_url);
}
});
}
/**
* Showing Dialog
* */
@Override
protected Dialog onCreateDialog(int id) {
switch (id) {
case progress_bar_type: // we set this to 0
pDialog = new ProgressDialog(this);
pDialog.setMessage("Downloading file. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setMax(100);
pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
pDialog.setCancelable(true);
pDialog.show();
return pDialog;
default:
return null;
}
}
/**
* Background Async Task to download file
* */
class DownloadFileFromURL extends AsyncTask<String, String, String> {
private SSLContext context;
/**
* Before starting background thread
* Show Progress Bar Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
showDialog(progress_bar_type);
}
/**
* Downloading file in background thread
* */
@Override
protected String doInBackground(String... f_url) {
int count;
try {
此行是以下错误：网址url =新网址（f_url [0]）;
HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
// Load the truststore that includes self-signed cert as a "trusted" entry.
KeyStore truststore;
truststore = KeyStore.getInstance("BKS");
InputStream in = getActivity().getResources().openRawResource(R.raw.mykeystore);
truststore.load(in, "mysecret".toCharArray());
TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
trustManagerFactory.init(truststore);
// Create custom SSL context that incorporates that truststore
SSLContext sslContext = SSLContext.getInstance("TLS");
sslContext.init(null, trustManagerFactory.getTrustManagers(), null);
connection.setSSLSocketFactory(sslContext.getSocketFactory());
connection.connect();
// this will be useful so that you can show a tipical 0-100% progress bar
int lenghtOfFile = connection.getContentLength();
// download the file
InputStream input = new BufferedInputStream(connection.getInputStream(), 8192);
// Output stream
OutputStream output = new FileOutputStream("/sdcard/downloadedfile.pdf");
byte data[] = new byte[1024];
long total = 0;
while ((count = input.read(data)) != -1) {
total += count;
// publishing the progress....
// After this onProgressUpdate will be called
publishProgress(""+(int)((total*100)/lenghtOfFile));
// writing data to file
output.write(data, 0, count);
}
// flushing output
output.flush();
// closing streams
output.close();
input.close();
} catch (Exception e) {
Log.e("Error: ", e.getMessage());
}
return null;
}
private ContextWrapper getActivity() {
// TODO Auto-generated method stub
return null;
}
/**
* Updating progress bar
* */
protected void onProgressUpdate(String... progress) {
// setting progress percentage
pDialog.setProgress(Integer.parseInt(progress[0]));
}
/**
* After completing background task
* Dismiss the progress dialog
* **/
@Override
protected void onPostExecute(String file_url) {
// dismiss the dialog after the file was downloaded
dismissDialog(progress_bar_type);
// Displaying downloaded image into image view
// Reading image path from sdcard
String imagePath = Environment.getExternalStorageDirectory().toString() + "/downloadedfile.pdf";
// setting downloaded into image view
my_image.setImageDrawable(Drawable.createFromPath(imagePath));
}
}
}
这是我的Logcat：
03-21 16:36:26.747: E/AndroidRuntime(5751): FATAL EXCEPTION: AsyncTask #1
03-21 16:36:26.747: E/AndroidRuntime(5751): Process: com.example.test2, PID: 5751
03-21 16:36:26.747: E/AndroidRuntime(5751): java.lang.RuntimeException: An error occured while executing doInBackground()
03-21 16:36:26.747: E/AndroidRuntime(5751): at android.os.AsyncTask$3.done(AsyncTask.java:300)
03-21 16:36:26.747: E/AndroidRuntime(5751): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
03-21 16:36:26.747: E/AndroidRuntime(5751): at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
03-21 16:36:26.747: E/AndroidRuntime(5751): at java.util.concurrent.FutureTask.run(FutureTask.java:242)
03-21 16:36:26.747: E/AndroidRuntime(5751): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
03-21 16:36:26.747: E/AndroidRuntime(5751): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
03-21 16:36:26.747: E/AndroidRuntime(5751): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
03-21 16:36:26.747: E/AndroidRuntime(5751): at java.lang.Thread.run(Thread.java:841)
03-21 16:36:26.747: E/AndroidRuntime(5751): Caused by: java.lang.NullPointerException: println needs a message
03-21 16:36:26.747: E/AndroidRuntime(5751): at android.util.Log.println_native(Native Method)
03-21 16:36:26.747: E/AndroidRuntime(5751): at android.util.Log.e(Log.java:232)
03-21 16:36:26.747: E/AndroidRuntime(5751): at com.example.test1.MainActivity$DownloadFileFromURL.doInBackground(MainActivity.java:194)
03-21 16:36:26.747: E/AndroidRuntime(5751): at com.example.test1.MainActivity$DownloadFileFromURL.doInBackground(MainActivity.java:1)
03-21 16:36:26.747: E/AndroidRuntime(5751): at android.os.AsyncTask$2.call(AsyncTask.java:288)
03-21 16:36:26.747: E/AndroidRuntime(5751): at java.util.concurrent.FutureTask.run(FutureTask.java:237)
03-21 16:36:26.747: E/AndroidRuntime(5751): ... 4 more
Stacktrace输出
03-21 18:39:45.957: W/System.err(2061): java.lang.NullPointerException
03-21 18:39:45.967: W/System.err(2061): at com.example.test1.MainActivity$DownloadFileFromURL.doInBackground(MainActivity.java:147)
03-21 18:39:45.967: W/System.err(2061): at com.example.test1.MainActivity$DownloadFileFromURL.doInBackground(MainActivity.java:1)
03-21 18:39:45.967: W/System.err(2061): at android.os.AsyncTask$2.call(AsyncTask.java:288)
03-21 18:39:45.967: W/System.err(2061): at java.util.concurrent.FutureTask.run(FutureTask.java:237)
03-21 18:39:45.967: W/System.err(2061): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
03-21 18:39:45.967: W/System.err(2061): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
03-21 18:39:45.967: W/System.err(2061): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
03-21 18:39:45.967: W/System.err(2061): at java.lang.Thread.run(Thread.java:841)
答案 0 :(得分：0)
尝试
Log.e("Error:", " " + e.getMessage());
而不是Log.e（＆＃34;错误：＆＃34;，e.getMessage（））;
// e.getMessage（）可以为null或为空。
还添加catch（MalformedURLException e）{}并查看为什么抛出url异常
答案 1 :(得分：0)
使您的AsyncTask扩展AsyncTask<String, Void, String>。