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我是android應用程序開發的新手，我正在開發一個android應用程序以讀取包含頻譜數據的.txt文件。該文件包含整數和空格，因此讀取每行後，代碼會修剪該字符串以刪除空格，然後將包含字符串的字符串轉換爲整數。整數表示Y座標值，行號表示X座標值。我必須繪製散點圖，並且我正在使用Achartengine。當我嘗試在模擬器上運行應用程序時，應用程序崩潰。日誌貓給出了這樣的信息閱讀Android應用程序的文件中的Java空指針異常
06-22 09:08:58.114: E/AndroidRuntime(1015): FATAL EXCEPTION: main
06-22 09:08:58.114: E/AndroidRuntime(1015): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.spec1readertest/com.example.spec1readertest.MainActivity}: java.lang.NullPointerException
06-22 09:08:58.114: E/AndroidRuntime(1015): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
06-22 09:08:58.114: E/AndroidRuntime(1015): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
06-22 09:08:58.114: E/AndroidRuntime(1015): at android.app.ActivityThread.access$600(ActivityThread.java:141)
06-22 09:08:58.114: E/AndroidRuntime(1015): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
06-22 09:08:58.114: E/AndroidRuntime(1015): at android.os.Handler.dispatchMessage(Handler.java:99)
06-22 09:08:58.114: E/AndroidRuntime(1015): at android.os.Looper.loop(Looper.java:137)
06-22 09:08:58.114: E/AndroidRuntime(1015): at android.app.ActivityThread.main(ActivityThread.java:5103)
06-22 09:08:58.114: E/AndroidRuntime(1015): at java.lang.reflect.Method.invokeNative(Native Method)
06-22 09:08:58.114: E/AndroidRuntime(1015): at java.lang.reflect.Method.invoke(Method.java:525)
06-22 09:08:58.114: E/AndroidRuntime(1015): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
06-22 09:08:58.114: E/AndroidRuntime(1015): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
06-22 09:08:58.114: E/AndroidRuntime(1015): at dalvik.system.NativeStart.main(Native Method)
06-22 09:08:58.114: E/AndroidRuntime(1015): Caused by: java.lang.NullPointerException
06-22 09:08:58.114: E/AndroidRuntime(1015): at com.example.spec1readertest.MainActivity.onStart(MainActivity.java:89)
06-22 09:08:58.114: E/AndroidRuntime(1015): at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
06-22 09:08:58.114: E/AndroidRuntime(1015): at android.app.Activity.performStart(Activity.java:5143)
06-22 09:08:58.114: E/AndroidRuntime(1015): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
06-22 09:08:58.114: E/AndroidRuntime(1015): ... 11 more
這是主要的activity.java文件
package com.example.spec1readertest;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import org.achartengine.GraphicalView;
import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.Toast;
public class MainActivity extends Activity {
ScatterGraphPlot scatter;
GraphicalView view;
LinearLayout layout;
EditText filename;
String filepath;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
filename = (EditText) findViewById(R.id.filename);
// Initialize loadspec btn
Button loadspec = (Button) findViewById(R.id.button2);
loadspec.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// filename input
filepath =filename.getText().toString();
//set file path
try {
filepath = "/sdcard/"+filepath+".txt";
BufferedReader br = new BufferedReader(new FileReader(filepath));
String specData = "";
int specVal;
int channelVal=1;
while ((specData = br.readLine()) != null) {
// Method for converting the text read from file to an integer
specVal=scatter.StringToNumber(specData);
// adding points to XYseries
scatter.addPoints(channelVal, specVal);
//repainting the view;
view.repaint();
//setting the specData string to an empty string
specData="";
//incrementing the channel value
channelVal++;
}
}
catch (IOException e) {
Toast.makeText(getBaseContext(),"file not found",Toast.LENGTH_SHORT).show();
}
}
});
// initialize exit button
Button exit = (Button) findViewById(R.id.button3);
exit.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
finish(); // exits the application
}
});
}
protected void onStart() {
super.onStart();
view = scatter.getView(this);
layout = (LinearLayout) findViewById(R.id.chart);
layout.addView(view);
}
}
這是我使用的繪製圖
public ScatterGraphPlot() {
// adding series to xymultiple series dataset
dataset.addSeries(series1);
// customizing the points on scatter graph
renderer.setColor(Color.GREEN);
renderer.setPointStyle(PointStyle.CIRCLE);
renderer.setFillPoints(true);
// customizing the entire graph
mRenderer.addSeriesRenderer(renderer);
mRenderer.setAxesColor(Color.WHITE);
mRenderer.setBackgroundColor(Color.BLACK);
mRenderer.setApplyBackgroundColor(true);
mRenderer.setZoomButtonsVisible(true);
}
public GraphicalView getView(Context context) {
//returning the graphical view to the main activity
view = ChartFactory.getScatterChartView(context, dataset, mRenderer);
return view;
}
public void addPoints(int x, int y) {
chval = x;
specval = y;
//add points to series1
series1.add(chval, specval);
}
//this method converts string to a number
int StringToNumber(String str) {
NumConvStr = str;
NumConvStr=NumConvStr.trim();
try {
RetNum = Integer.parseInt(NumConvStr);
return RetNum;
}
//ignore catch block :assuming file to be error free
catch (NumberFormatException e) {
return 0;
}
}
}
的的ScatterGraphPlot.java文件我的應用程序的XML文件是
<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"
tools:context="${packageName}.${activityClass}" >
<Button
android:id="@+id/button3"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/button2"
android:layout_alignBottom="@+id/button2"
android:layout_alignParentRight="true"
android:layout_marginRight="20dp"
android:text="@string/Close" />
<EditText
android:id="@+id/filename"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:layout_marginTop="20dp"
android:ems="10"
android:hint="@string/filename" />
<Button
android:id="@+id/button2"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/filename"
android:layout_marginLeft="22dp"
android:layout_marginTop="20dp"
android:text="@string/loadspec" />
<LinearLayout
android:id="@+id/chart"
android:layout_width="match_parent"
android:layout_height="250dp"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_marginBottom="26dp"
android:orientation="vertical" >
</LinearLayout>
</RelativeLayout>
我希望有人會幫我解決這個問題。
看看'MainActivity.java'行89就像你的堆棧跟蹤所告知的那樣。或者至少告訴我們它在代碼中的哪一行;）看起來像分散或佈局可能爲空。取決於第89行的位置。 –
*方法*代碼太多，請創建[SSCCE]（http://sscce.org）。 –
+1 Big Fan的SSCCE.org;）@BaummitAugen –