嗨，这是我的第一篇文章，很抱歉，如果我犯了任何错误。
这是我的问题：我正在编写一个应用程序，当您单击一个按钮然后将其发送到FTP服务器时，如果您单击另一个按钮，该应用程序应将今天的日期保存在txt文件中。我使用Apache commons库进行FTP连接。
这是我的MainActivity：
package com.example.timestamp;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.text.DateFormat;
import java.util.Date;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import it.sauronsoftware.ftp4j.FTPClient;
public class MainActivity extends Activity {
private static final String TAG = MainActivity.class.getName();
final File log = new File("TimeStampLog.txt");
final String SERVER = "***************";
final String USERNAME = "**************";
final String PASSWORD = "*************";
final int PORT = 21;
final TextView tv = (TextView) findViewById(R.id.textView1);
Button save = (Button) findViewById(R.id.save);
Button send = (Button) findViewById(R.id.send);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
save.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
String date = DateFormat.getDateTimeInstance().format(new Date());
tv.setText(date);
StringBuilder sb = new StringBuilder();
sb.append(date);
sb.append("\r\n");
sb.append(readFromFile());
writeToFile(sb.toString());
}
});
send.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
uploadFile(log);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void uploadFile(File fileName) {
FTPClient client = new FTPClient();
try {
client.connect(SERVER, 21);
client.login(USERNAME, PASSWORD);
client.setType(FTPClient.TYPE_BINARY);
client.upload(log);
} catch (Exception e) {
e.printStackTrace();
try {
client.disconnect(true);
} catch (Exception e2) {
e2.printStackTrace();
}
}
}
private void writeToFile(String data) {
try {
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(
openFileOutput(log.getName(), Context.MODE_PRIVATE));
outputStreamWriter.write(data);
outputStreamWriter.flush();
outputStreamWriter.close();
} catch (IOException e) {
Log.e(TAG, "File write failed: " + e.toString());
}
}
private String readFromFile() {
String ret = "";
try {
InputStream inputStream = openFileInput(log.getName());
if (inputStream != null) {
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
String receiveString = "";
StringBuilder stringBuilder = new StringBuilder();
while ((receiveString = bufferedReader.readLine()) != null) {
stringBuilder.append(receiveString);
stringBuilder.append("\r\n");
}
inputStream.close();
ret = stringBuilder.toString();
}
} catch (FileNotFoundException e) {
Log.e(TAG, "File not found: " + e.toString());
} catch (IOException e) {
Log.e(TAG, "Can not read file: " + e.toString());
}
return ret;
}
}
我的XML文件：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.timestamp.MainActivity" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:ems="10" />
<Button
android:id="@+id/save"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/textView1"
android:layout_below="@+id/textView1"
android:layout_marginTop="60dp"
android:text="@string/save" />
<Button
android:id="@+id/send"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/save"
android:layout_alignBottom="@+id/save"
android:layout_alignParentRight="true"
android:text="@string/send" />
</RelativeLayout>
这是LogCat输出：
08-14 13:51:45.919: E/AndroidRuntime(14598): FATAL EXCEPTION: main
08-14 13:51:45.919: E/AndroidRuntime(14598): Process: com.example.timestamp, PID: 14598
08-14 13:51:45.919: E/AndroidRuntime(14598): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.timestamp/com.example.timestamp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
08-14 13:51:45.919: E/AndroidRuntime(14598): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
08-14 13:51:45.919: E/AndroidRuntime(14598): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
08-14 13:51:45.919: E/AndroidRuntime(14598): at android.app.ActivityThread.access$800(ActivityThread.java:144)
08-14 13:51:45.919: E/AndroidRuntime(14598): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
08-14 13:51:45.919: E/AndroidRuntime(14598): at android.os.Handler.dispatchMessage(Handler.java:102)
08-14 13:51:45.919: E/AndroidRuntime(14598): at android.os.Looper.loop(Looper.java:135)
08-14 13:51:45.919: E/AndroidRuntime(14598): at android.app.ActivityThread.main(ActivityThread.java:5221)
08-14 13:51:45.919: E/AndroidRuntime(14598): at java.lang.reflect.Method.invoke(Native Method)
08-14 13:51:45.919: E/AndroidRuntime(14598): at java.lang.reflect.Method.invoke(Method.java:372)
08-14 13:51:45.919: E/AndroidRuntime(14598): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
08-14 13:51:45.919: E/AndroidRuntime(14598): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
08-14 13:51:45.919: E/AndroidRuntime(14598): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
08-14 13:51:45.919: E/AndroidRuntime(14598): at android.app.Activity.findViewById(Activity.java:2071)
08-14 13:51:45.919: E/AndroidRuntime(14598): at com.example.timestamp.MainActivity.<init>(MainActivity.java:33)
08-14 13:51:45.919: E/AndroidRuntime(14598): at java.lang.reflect.Constructor.newInstance(Native Method)
08-14 13:51:45.919: E/AndroidRuntime(14598): at java.lang.Class.newInstance(Class.java:1572)
08-14 13:51:45.919: E/AndroidRuntime(14598): at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
08-14 13:51:45.919: E/AndroidRuntime(14598): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
08-14 13:51:45.919: E/AndroidRuntime(14598): ... 10 more
是的我将互联网添加到使用权限
中我认为问题可能是我需要另一个用于FTP实现的线程，我尝试使用AsyncTask和Handler，但我一直遇到同样的错误。
答案 0 :(得分：0)
从LogCat输出我可以看到你得到NullPointerException，因为你已经初始化了我们可以声明任何变量的Button和TextView。
在 OnCreate（）方法中调用 setContentView（R.layout.activity_main）; 之前，您已初始化并充气所有按钮和TextView。您已在OnCreate方法中移动代码，然后尝试上传文件。
您可以尝试以下代码：
package com.example.timestamp;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.text.DateFormat;
import java.util.Date;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import it.sauronsoftware.ftp4j.FTPClient;
public class MainActivity extends Activity {
private static final String TAG = MainActivity.class.getName();
final File log = new File("TimeStampLog.txt");
final String SERVER = "***************";
final String USERNAME = "**************";
final String PASSWORD = "*************";
final int PORT = 21;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final TextView tv = (TextView) findViewById(R.id.textView1);
Button save = (Button) findViewById(R.id.save);
Button send = (Button) findViewById(R.id.send);
save.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
String date = DateFormat.getDateTimeInstance().format(new Date());
tv.setText(date);
StringBuilder sb = new StringBuilder();
sb.append(date);
sb.append("\r\n");
sb.append(readFromFile());
writeToFile(sb.toString());
}
});
send.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
uploadFile(log);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void uploadFile(File fileName) {
FTPClient client = new FTPClient();
try {
client.connect(SERVER, 21);
client.login(USERNAME, PASSWORD);
client.setType(FTPClient.TYPE_BINARY);
client.upload(log);
} catch (Exception e) {
e.printStackTrace();
try {
client.disconnect(true);
} catch (Exception e2) {
e2.printStackTrace();
}
}
}
private void writeToFile(String data) {
try {
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(
openFileOutput(log.getName(), Context.MODE_PRIVATE));
outputStreamWriter.write(data);
outputStreamWriter.flush();
outputStreamWriter.close();
} catch (IOException e) {
Log.e(TAG, "File write failed: " + e.toString());
}
}
private String readFromFile() {
String ret = "";
try {
InputStream inputStream = openFileInput(log.getName());
if (inputStream != null) {
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
String receiveString = "";
StringBuilder stringBuilder = new StringBuilder();
while ((receiveString = bufferedReader.readLine()) != null) {
stringBuilder.append(receiveString);
stringBuilder.append("\r\n");
}
inputStream.close();
ret = stringBuilder.toString();
}
} catch (FileNotFoundException e) {
Log.e(TAG, "File not found: " + e.toString());
} catch (IOException e) {
Log.e(TAG, "Can not read file: " + e.toString());
}
return ret;
}
}
我希望它有所帮助！