我正在测试一个应用程序，它可以在点击按钮时下载文件。但当点击按钮时，什么也不会发生。对话框会在几分之一秒内出现并消失。不知道怎么了这是我的代码
主要活动
public class MainActivity extends Activity
{
public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
private Button startBtn;
private ProgressDialog mProgressDialog;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
startBtn = (Button) findViewById(R.id.mainButton);
startBtn.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View p1)
{
// TODO: Implement this method
startDownload();
}
});
}
private void startDownload()
{
String url = "http://farm1.static.flickr.com/114/298125983_0e4bf66782_b.jpg";
new DownloadFileAsync().execute(url);
}
@Override protected Dialog onCreateDialog(int id)
{
switch (id)
{
case DIALOG_DOWNLOAD_PROGRESS: mProgressDialog = new ProgressDialog(this);
mProgressDialog.setMessage("Downloading file..");
mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
mProgressDialog.setCancelable(false);
mProgressDialog.show();
return mProgressDialog;
default: return null;
}
}
class DownloadFileAsync extends AsyncTask<String, String, String>
{
@Override protected void onPreExecute()
{
super.onPreExecute();
showDialog(DIALOG_DOWNLOAD_PROGRESS);
}
@Override protected String doInBackground(String... aurl)
{
int count;
try
{
URL url = new URL(aurl[0]);
URLConnection conexion = url.openConnection(); conexion.connect();
int lenghtOfFile = conexion.getContentLength();
Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile);
InputStream input = new BufferedInputStream(url.openStream());
OutputStream output = new FileOutputStream("/sdcard/some_photo_from_gdansk_poland.jpg");
byte data[] = new byte[1024];
long total = 0; while ((count = input.read(data)) != -1)
{
total += count;
publishProgress("" + (int)((total * 100) / lenghtOfFile));
output.write(data, 0, count);
}
output.flush();
output.close();
input.close();
}
catch (Exception e)
{
}
return null;
} protected void onProgressUpdate(String... progress)
{
Log.d("ANDRO_ASYNC", progress[0]);
mProgressDialog.setProgress(Integer.parseInt(progress[0]));
} @Override protected void onPostExecute(String unused)
{
dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
}
}
}
Android清单
<?xml version="1.0" encoding="utf-8"?>
uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
这是工作代码。。
import java.io.DataOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import android.app.ProgressDialog;
import android.media.AudioManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Log.e("Starting : ", "Starting...");
((TextView) findViewById(R.id.status)).setText("Starting...");
// execute this when the downloader must be fired
final getAppInfo downloadTask = new getAppInfo();
downloadTask.execute("http://farm1.static.flickr.com/114/298125983_0e4bf66782_b.jpg");
}
private class getAppInfo extends AsyncTask<String, String, String> {
/** The system calls this to perform work in a worker thread and
* delivers it the parameters given to AsyncTask.execute() */
ProgressDialog dialog;
@Override
protected void onPreExecute() {
dialog = new ProgressDialog(MainActivity.this);
dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
dialog.setMessage("Loading");
dialog.setIndeterminate(false);
dialog.setCancelable(false);
dialog.setMax(100);
dialog.setProgress(100);
dialog.show();
}
@Override
protected String doInBackground(String... urls) {
InputStream input = null;
OutputStream output = null;
HttpURLConnection connection = null;
try {
URL url = new URL(urls[0]);
connection = (HttpURLConnection) url.openConnection();
connection.setDoOutput(true);
connection.setDoInput(true);
connection.setRequestMethod("POST");
connection.setRequestProperty("Content-Type", "application/json");
connection.setUseCaches(false);
connection.connect();
String length = connection.getHeaderField("Content-length");
Log.e("fileLength : ",""+length);
// expect HTTP 200 OK, so we don't mistakenly save error report
// instead of the file
if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
return "Server returned HTTP " + connection.getResponseCode()
+ " " + connection.getResponseMessage();
}
// this will be useful to display download percentage
// might be -1: server did not report the length
int fileLength = connection.getContentLength();
Log.e("fileLength : ",""+fileLength);
// download the file
input = connection.getInputStream();
// final String resultt = org.apache.commons.io.IOUtils.toString(input, "UTF-8");
// Log.e("Response : ",""+resultt);
output = new FileOutputStream(Environment.getExternalStorageDirectory().getAbsolutePath()+"/testsql.jpg");
byte data[] = new byte[4096];
long total = 0;
int count;
while ((count = input.read(data)) != -1) {
// allow canceling with back button
if (isCancelled()) {
input.close();
return null;
}
total += count;
// publishing the progress....
if (fileLength > 0) // only if total length is known
publishProgress(""+(int) (total * 100 / fileLength));
output.write(data, 0, count);
}
} catch (Exception e) {
Log.e("exception : ",""+e.getMessage());
return e.toString();
} finally {
try {
if (output != null)
output.close();
if (input != null)
input.close();
} catch (IOException ignored) {
}
if (connection != null)
connection.disconnect();
}
return null;
}
@Override
protected void onProgressUpdate(String... progress) {
Log.v("count",progress[0]);
dialog.setProgress(Integer.parseInt(progress[0]));
}
/** The system calls this to perform work in the UI thread and delivers
* the result from doInBackground() */
@Override
protected void onPostExecute(String result) {
//dialog.setProgress(100);
if(dialog!=null) dialog.dismiss();
}
}
}
Handler handler = new Handler();
class DownloadFileAsync extends AsyncTask<Void, Integer, String> {
ProgressDialog progressDialog;
Context context;
String downloadUrl;
// shared preferences
SharedPreferences sharedPreferences;
int state;
public DownloadFileAsync(Context context, String downloadUrl) {
this.context = context;
this.downloadUrl = downloadUrl;
}
@Override
protected void onPreExecute() {
handler.post(new Runnable() {
@Override
public void run() {
progressDialog = new ProgressDialog(context);
progressDialog.setMessage("Downloading file. Please wait......");
progressDialog.setIndeterminate(false);
progressDialog.setMax(100);
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
progressDialog.show();
}
});
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
progressDialog.setProgress(values[0]);
}
@Override
protected String doInBackground(Void... params) {
int count;
try {
URL url = new URL(downloadUrl.toString());
URLConnection conection = url.openConnection();
conection.setReadTimeout(5000);
conection.connect();
// getting file length
int lenghtOfFile = conection.getContentLength();
if (lenghtOfFile > 0) {
// input stream to read file - with 8k buffer
InputStream input = new BufferedInputStream(url.openStream(), 8192);
// Output stream to write file
OutputStream output = new FileOutputStream(
Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)
+ "/data.jpg");
byte data[] = new byte[1024];
long total = 0;
Log.d("lenghtOfFile", "---" + lenghtOfFile);
while ((count = input.read(data)) != -1) {
total += count;
// writing data to file
output.write(data, 0, count);
// publishing the progress. After this onProgressUpdate
// will be called
publishProgress((int) ((total * 100) / lenghtOfFile));
}
// flushing output
output.flush();
// closing streams
output.close();
input.close();
}
} catch (Exception e) {
Log.e("Error: ", e.getMessage());
}
return null;
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
if (progressDialog != null && progressDialog.isShowing()) {
progressDialog.dismiss();
}
}
}
点击按钮后，像下面的一样调用它
new DownloadFileAsync(MainActivity.this, url).execute();
它工作并在清单中添加以下权限
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />