使用我的Android应用程序，我在从另一个活动打开活动时遇到此异常。我需要你帮助确定我的代码应该从哪里开始解决问题：
04-16 19:55:43.014: I/MemoryCache(1083): MemoryCache will use up to 4.0MB
04-16 19:55:43.044: D/AndroidRuntime(1083): Shutting down VM
04-16 19:55:43.054: W/dalvikvm(1083): threadid=1: thread exiting with uncaught exception (group=0xb4a53ba8)
04-16 19:55:43.124: E/AndroidRuntime(1083): FATAL EXCEPTION: main
04-16 19:55:43.124: E/AndroidRuntime(1083): Process: com.solinpromex.vivegrancanaria, PID: 1083
04-16 19:55:43.124: E/AndroidRuntime(1083): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.solinpromex.vivegrancanaria/com.solinpromex.vivegrancanaria.Empresas_SingleItemView}: java.lang.NullPointerException
04-16 19:55:43.124: E/AndroidRuntime(1083): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
04-16 19:55:43.124: E/AndroidRuntime(1083): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
04-16 19:55:43.124: E/AndroidRuntime(1083): at android.app.ActivityThread.access$800(ActivityThread.java:135)
04-16 19:55:43.124: E/AndroidRuntime(1083): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
04-16 19:55:43.124: E/AndroidRuntime(1083): at android.os.Handler.dispatchMessage(Handler.java:102)
04-16 19:55:43.124: E/AndroidRuntime(1083): at android.os.Looper.loop(Looper.java:136)
04-16 19:55:43.124: E/AndroidRuntime(1083): at android.app.ActivityThread.main(ActivityThread.java:5017)
04-16 19:55:43.124: E/AndroidRuntime(1083): at java.lang.reflect.Method.invokeNative(Native Method)
04-16 19:55:43.124: E/AndroidRuntime(1083): at java.lang.reflect.Method.invoke(Method.java:515)
04-16 19:55:43.124: E/AndroidRuntime(1083): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-16 19:55:43.124: E/AndroidRuntime(1083): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-16 19:55:43.124: E/AndroidRuntime(1083): at dalvik.system.NativeStart.main(Native Method)
04-16 19:55:43.124: E/AndroidRuntime(1083): Caused by: java.lang.NullPointerException
04-16 19:55:43.124: E/AndroidRuntime(1083): at android.content.ContextWrapper.getCacheDir(ContextWrapper.java:230)
04-16 19:55:43.124: E/AndroidRuntime(1083): at com.solinpromex.vivegrancanaria.FileCache.<init>(FileCache.java:17)
04-16 19:55:43.124: E/AndroidRuntime(1083): at com.solinpromex.vivegrancanaria.ImageLoader.<init>(ImageLoader.java:34)
04-16 19:55:43.124: E/AndroidRuntime(1083): at com.solinpromex.vivegrancanaria.Empresas_SingleItemView.<init>(Empresas_SingleItemView.java:16)
04-16 19:55:43.124: E/AndroidRuntime(1083): at java.lang.Class.newInstanceImpl(Native Method)
04-16 19:55:43.124: E/AndroidRuntime(1083): at java.lang.Class.newInstance(Class.java:1208)
04-16 19:55:43.124: E/AndroidRuntime(1083): at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
04-16 19:55:43.124: E/AndroidRuntime(1083): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
04-16 19:55:43.124: E/AndroidRuntime(1083): ... 11 more
已编辑：已添加Empresa.SingleItemView.java：
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.ImageView;
import android.widget.TextView;
public class Empresas_SingleItemView extends Activity {
// Declare Variables
String valoracionEmpresa;
String nombreEmpresa;
String direccionEmpresa;
String imagenstrImagen;
String position;
ImageLoader imageLoader = new ImageLoader(this);
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Get the view from singleitemview.xml
setContentView(R.layout.empresas_singleitemview);
Intent i = getIntent();
// Get the result of rank
valoracionEmpresa = i.getStringExtra("valoracionEmpresa");
// Get the result of country
nombreEmpresa = i.getStringExtra("nombreEmpresa");
// Get the result of population
direccionEmpresa = i.getStringExtra("direccionEmpresa");
// Get the result of flag
imagenstrImagen = i.getStringExtra("strImagen");
// Locate the TextViews in singleitemview.xml
TextView txtvaloracionempresa = (TextView) findViewById(R.id.valoracionEmpresa);
TextView txtnombreempresa = (TextView) findViewById(R.id.nombreEmpresa);
TextView txtdireccionempresa = (TextView) findViewById(R.id.direccionEmpresa);
// Locate the ImageView in singleitemview.xml
ImageView imagenEmpresa = (ImageView) findViewById(R.id.strImagen);
// Set results to the TextViews
txtvaloracionempresa.setText(valoracionEmpresa);
txtnombreempresa.setText(nombreEmpresa);
txtdireccionempresa.setText(direccionEmpresa);
// Capture position and set results to the ImageView
// Passes flag images URL into ImageLoader.class
imageLoader.DisplayImage(imagenstrImagen, imagenEmpresa);
}
}
添加了FileCache.java
import java.io.File;
import android.content.Context;
public class FileCache {
private File cacheDir;
public FileCache(Context context) {
// Find the dir to save cached images
if (android.os.Environment.getExternalStorageState().equals(
android.os.Environment.MEDIA_MOUNTED))
cacheDir = new File(
android.os.Environment.getExternalStorageDirectory(),
"JsonParseTutorialCache");
else
cacheDir = context.getCacheDir();
if (!cacheDir.exists())
cacheDir.mkdirs();
}
public File getFile(String url) {
String filename = String.valueOf(url.hashCode());
// String filename = URLEncoder.encode(url);
File f = new File(cacheDir, filename);
return f;
}
public void clear() {
File[] files = cacheDir.listFiles();
if (files == null)
return;
for (File f : files)
f.delete();
}
}
添加了ImageLoader.java
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
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 java.util.Collections;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import android.os.Handler;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.widget.ImageView;
public class ImageLoader {
MemoryCache memoryCache = new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews = Collections
.synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;
// Handler to display images in UI thread
Handler handler = new Handler();
public ImageLoader(Context context) {
fileCache = new FileCache(context);
executorService = Executors.newFixedThreadPool(5);
}
final int stub_id = R.drawable.temp_img;
public void DisplayImage(String url, ImageView imageView) {
imageViews.put(imageView, url);
Bitmap bitmap = memoryCache.get(url);
if (bitmap != null)
imageView.setImageBitmap(bitmap);
else {
queuePhoto(url, imageView);
imageView.setImageResource(stub_id);
}
}
private void queuePhoto(String url, ImageView imageView) {
PhotoToLoad p = new PhotoToLoad(url, imageView);
executorService.submit(new PhotosLoader(p));
}
private Bitmap getBitmap(String url) {
File f = fileCache.getFile(url);
Bitmap b = decodeFile(f);
if (b != null)
return b;
// Download Images from the Internet
try {
Bitmap bitmap = null;
URL imageUrl = new URL(url);
HttpURLConnection conn = (HttpURLConnection) imageUrl
.openConnection();
conn.setConnectTimeout(30000);
conn.setReadTimeout(30000);
conn.setInstanceFollowRedirects(true);
InputStream is = conn.getInputStream();
OutputStream os = new FileOutputStream(f);
Utils.CopyStream(is, os);
os.close();
conn.disconnect();
bitmap = decodeFile(f);
return bitmap;
} catch (Throwable ex) {
ex.printStackTrace();
if (ex instanceof OutOfMemoryError)
memoryCache.clear();
return null;
}
}
// Decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f) {
try {
// Decode image size
BitmapFactory.Options o = new BitmapFactory.Options();
o.inJustDecodeBounds = true;
FileInputStream stream1 = new FileInputStream(f);
BitmapFactory.decodeStream(stream1, null, o);
stream1.close();
// Find the correct scale value. It should be the power of 2.
// Recommended Size 512
final int REQUIRED_SIZE = 70;
int width_tmp = o.outWidth, height_tmp = o.outHeight;
int scale = 1;
while (true) {
if (width_tmp / 2 < REQUIRED_SIZE
|| height_tmp / 2 < REQUIRED_SIZE)
break;
width_tmp /= 2;
height_tmp /= 2;
scale *= 2;
}
// Decode with inSampleSize
BitmapFactory.Options o2 = new BitmapFactory.Options();
o2.inSampleSize = scale;
FileInputStream stream2 = new FileInputStream(f);
Bitmap bitmap = BitmapFactory.decodeStream(stream2, null, o2);
stream2.close();
return bitmap;
} catch (FileNotFoundException e) {
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
// Task for the queue
private class PhotoToLoad {
public String url;
public ImageView imageView;
public PhotoToLoad(String u, ImageView i) {
url = u;
imageView = i;
}
}
class PhotosLoader implements Runnable {
PhotoToLoad photoToLoad;
PhotosLoader(PhotoToLoad photoToLoad) {
this.photoToLoad = photoToLoad;
}
@Override
public void run() {
try {
if (imageViewReused(photoToLoad))
return;
Bitmap bmp = getBitmap(photoToLoad.url);
memoryCache.put(photoToLoad.url, bmp);
if (imageViewReused(photoToLoad))
return;
BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
handler.post(bd);
} catch (Throwable th) {
th.printStackTrace();
}
}
}
boolean imageViewReused(PhotoToLoad photoToLoad) {
String tag = imageViews.get(photoToLoad.imageView);
if (tag == null || !tag.equals(photoToLoad.url))
return true;
return false;
}
// Used to display bitmap in the UI thread
class BitmapDisplayer implements Runnable {
Bitmap bitmap;
PhotoToLoad photoToLoad;
public BitmapDisplayer(Bitmap b, PhotoToLoad p) {
bitmap = b;
photoToLoad = p;
}
public void run() {
if (imageViewReused(photoToLoad))
return;
if (bitmap != null)
photoToLoad.imageView.setImageBitmap(bitmap);
else
photoToLoad.imageView.setImageResource(stub_id);
}
}
public void clearCache() {
memoryCache.clear();
fileCache.clear();
}
}
答案 0 :(得分：0)
经过长时间的讨论和搜索，我找到了问题所在。我还不知道如何解决它，但至少，我知道如何避免异常。 可能是明天，我会更新思，我会解决源问题，但是现在只需要执行app就可以了。 这里：
// Locate the TextViews in singleitemview.xml
TextView txtvaloracionempresa = (TextView) findViewById(R.id.valoracionEmpresa);
TextView txtnombreempresa = (TextView) findViewById(R.id.nombreEmpresa);
TextView txtdireccionempresa = (TextView) findViewById(R.id.direccionEmpresa);
// Locate the ImageView in singleitemview.xml
ImageView imagenEmpresa = (ImageView) findViewById(R.id.strImagen);
注释这些行（将//放在所有行上），未显示异常并显示活动Empresas_SingleItemView。当然，这些值并不是真正的价值，但现在解决方案的方式似乎非常简单。感谢您的支持。