我正在关注如何将图片上传到服务器的this教程，但我在dialog.dismiss();
return serverResponseCode;上获得了NullPointerException
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class UploadToServer extends Activity {
TextView messageText;
Button uploadButton;
int serverResponseCode = 0;
ProgressDialog dialog = null;
String upLoadServerUri = null;
/********** File Path *************/
final String uploadFilePath = "/mnt/sdcard/";
final String uploadFileName = "service_lifecycle.png";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_upload_to_server);
uploadButton = (Button)findViewById(R.id.uploadButton);
messageText = (TextView)findViewById(R.id.messageText);
messageText.setText("Uploading file path :- '/mnt/sdcard/"+uploadFileName+"'");
/************* Php script path ****************/
upLoadServerUri = "http://www.androidexample.com/media/UploadToServer.php";
uploadButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
dialog = ProgressDialog.show(UploadToServer.this, "", "Uploading file...", true);
new Thread(new Runnable() {
public void run() {
runOnUiThread(new Runnable() {
public void run() {
messageText.setText("uploading started.....");
}
});
uploadFile(uploadFilePath + "" + uploadFileName);
}
}).start();
}
});
}
public int uploadFile(String sourceFileUri) {
String fileName = sourceFileUri;
HttpURLConnection conn = null;
DataOutputStream dos = null;
String lineEnd = "\r\n";
String twoHyphens = "--";
String boundary = "*****";
int bytesRead, bytesAvailable, bufferSize;
byte[] buffer;
int maxBufferSize = 1 * 1024 * 1024;
File sourceFile = new File(sourceFileUri);
if (!sourceFile.isFile()) {
dialog.dismiss();
Log.e("uploadFile", "Source File not exist :"
+uploadFilePath + "" + uploadFileName);
runOnUiThread(new Runnable() {
public void run() {
messageText.setText("Source File not exist :"
+uploadFilePath + "" + uploadFileName);
}
});
return 0;
}
else
{
try {
// open a URL connection to the Servlet
FileInputStream fileInputStream = new FileInputStream(sourceFile);
URL url = new URL(upLoadServerUri);
// Open a HTTP connection to the URL
conn = (HttpURLConnection) url.openConnection();
conn.setDoInput(true); // Allow Inputs
conn.setDoOutput(true); // Allow Outputs
conn.setUseCaches(false); // Don't use a Cached Copy
conn.setRequestMethod("POST");
conn.setRequestProperty("Connection", "Keep-Alive");
conn.setRequestProperty("ENCTYPE", "multipart/form-data");
conn.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);
conn.setRequestProperty("uploaded_file", fileName);
dos = new DataOutputStream(conn.getOutputStream());
dos.writeBytes(twoHyphens + boundary + lineEnd);
dos.writeBytes("Content-Disposition: form-data; name="uploaded_file";filename=""
+ fileName + """ + lineEnd);
dos.writeBytes(lineEnd);
// create a buffer of maximum size
bytesAvailable = fileInputStream.available();
bufferSize = Math.min(bytesAvailable, maxBufferSize);
buffer = new byte[bufferSize];
// read file and write it into form...
bytesRead = fileInputStream.read(buffer, 0, bufferSize);
while (bytesRead > 0) {
dos.write(buffer, 0, bufferSize);
bytesAvailable = fileInputStream.available();
bufferSize = Math.min(bytesAvailable, maxBufferSize);
bytesRead = fileInputStream.read(buffer, 0, bufferSize);
}
// send multipart form data necesssary after file data...
dos.writeBytes(lineEnd);
dos.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);
// Responses from the server (code and message)
serverResponseCode = conn.getResponseCode();
String serverResponseMessage = conn.getResponseMessage();
Log.i("uploadFile", "HTTP Response is : "
+ serverResponseMessage + ": " + serverResponseCode);
if(serverResponseCode == 200){
runOnUiThread(new Runnable() {
public void run() {
String msg = "File Upload Completed.\n\n See uploaded file here : \n\n"
+" http://www.androidexample.com/media/uploads/"
+uploadFileName;
messageText.setText(msg);
Toast.makeText(UploadToServer.this, "File Upload Complete.",
Toast.LENGTH_SHORT).show();
}
});
}
//close the streams //
fileInputStream.close();
dos.flush();
dos.close();
} catch (MalformedURLException ex) {
dialog.dismiss();
ex.printStackTrace();
runOnUiThread(new Runnable() {
public void run() {
messageText.setText("MalformedURLException Exception : check script url.");
Toast.makeText(UploadToServer.this, "MalformedURLException",
Toast.LENGTH_SHORT).show();
}
});
Log.e("Upload file to server", "error: " + ex.getMessage(), ex);
} catch (Exception e) {
dialog.dismiss();
e.printStackTrace();
runOnUiThread(new Runnable() {
public void run() {
messageText.setText("Got Exception : see logcat ");
Toast.makeText(UploadToServer.this, "Got Exception : see logcat ",
Toast.LENGTH_SHORT).show();
}
});
Log.e("Upload file to server Exception", "Exception : "
+ e.getMessage(), e);
}
dialog.dismiss();
return serverResponseCode;
} // End else block
}
}
有谁知道如何修复它？
此外，有没有人知道如何从应用程序发送一些字符串值，以及如何在PHP中接收它？
答案 0 :(得分：0)
您正在后台线程中解雇对话框。您应该在 runOnUiThread 中执行此操作。
答案 1 :(得分：0)
我想提出一个ASyncTask明确的解决方案，而不是让它与线程复杂化。换句话说，使用Thread进行仅后台操作，并使用ASyncTask来处理UI线程。
以下是您的简短示例：
//[...]
// here is your handler for button:
uploadButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
new Uploader().execute(uploadFilePath + "" + uploadFileName);
});
//[...]
private class Uploader extends AsyncTask<String, Void, Boolean>
{
private ProgressDialog dialog;
@Override
protected void onPreExecute() {
super.onPreExecute();
dialog = ProgressDialog.show(UploadToServer.this, "", "Uploading file...", true);
messageText.setText("uploading started.....");
// do here all UI operations -> show Dialog window, change texts etc.
}
@Override
protected Boolean doInBackground(String... params) {
// do here background operation, e.g. connect to web
// return true for success, false for error
String fileToUpload = params[0]; // get file name that was sent from OnClick listener
return true;
}
@Override
protected void onPostExecute(Boolean result) {
super.onPostExecute(result);
// hide Dialogs here and update texts
dialog.dismiss();
if (result) {
// if success, show something
}
else {
// if error, show something
}
}
}
答案 2 :(得分：0)
您可以在活动中定义全局变量，例如
ProgressDialog dialog;
并在onCreate
中初始化它dialog = new ProgressDialog(UploadServer.this);
dialog.setMessage("Uploading..");
dialog.setCancelable(true);
dialog.setTitle("");
稍后您可以随时随地使用它。但在显示对话框之前，您应该检查
if(dialog != null && !dialog.isShowing())
dialog.show();
当你想要解散时
if(dialog != null && dialog.isShowing())
dialog.dismiss();
使用空检查可以避免空指针异常。
答案 3 :(得分：-1)
检查对话框！= null然后dismiss.as你在每个条件中写了dialog.dismiss（）我认为你试图解雇已经被解雇的对话