我的应用程序有问题，我正在从 JSON 加载时间线，没关系。现在我想单击一个项目并在单独的活动中查看它。事情是在我尝试放置图像之前一直有效。
为了更好地理解：
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.ImageView;
import android.widget.TextView;
public class SingleItemView extends Activity {
// Declare Variables
String country;
String population;
String flag;
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.singleitemview);
Intent i = getIntent();
// Get the result of rank
// Get the result of country
country = i.getStringExtra("country");
// Get the result of population
population = i.getStringExtra("population");
// Get the result of flag
flag = i.getStringExtra("flag");
// Locate the TextViews in singleitemview.xml
TextView txtcountry = (TextView) findViewById(R.id.country);
TextView txtpopulation = (TextView) findViewById(R.id.population);
// Locate the ImageView in singleitemview.xml
ImageView imgflag = (ImageView) findViewById(R.id.flag);
// Set results to the TextViews
txtcountry.setText(country);
txtpopulation.setText(population);
// Capture position and set results to the ImageView
// Passes flag images URL into ImageLoader.class
imageLoader.DisplayImage(flag, imgflag);
}
}
FileCache.java 是这个：
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(),
"GettfordCommunity");
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();
}
}
我已经在 AndroidManifest 上设置了写入外部存储的权限：
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
但是当我点击一个项目时，应用程序崩溃了：
10-07 16:57:47.586: E/AndroidRuntime(1772): FATAL EXCEPTION: main
10-07 16:57:47.586: E/AndroidRuntime(1772): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.gettford.community/com.gettford.community.SingleItemView}: java.lang.NullPointerException
10-07 16:57:47.586: E/AndroidRuntime(1772): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
10-07 16:57:47.586: E/AndroidRuntime(1772): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
10-07 16:57:47.586: E/AndroidRuntime(1772): at android.app.ActivityThread.access$600(ActivityThread.java:130)
10-07 16:57:47.586: E/AndroidRuntime(1772): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
10-07 16:57:47.586: E/AndroidRuntime(1772): at android.os.Handler.dispatchMessage(Handler.java:99)
10-07 16:57:47.586: E/AndroidRuntime(1772): at android.os.Looper.loop(Looper.java:137)
10-07 16:57:47.586: E/AndroidRuntime(1772): at android.app.ActivityThread.main(ActivityThread.java:4745)
10-07 16:57:47.586: E/AndroidRuntime(1772): at java.lang.reflect.Method.invokeNative(Native Method)
10-07 16:57:47.586: E/AndroidRuntime(1772): at java.lang.reflect.Method.invoke(Method.java:511)
10-07 16:57:47.586: E/AndroidRuntime(1772): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-07 16:57:47.586: E/AndroidRuntime(1772): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-07 16:57:47.586: E/AndroidRuntime(1772): at dalvik.system.NativeStart.main(Native Method)
10-07 16:57:47.586: E/AndroidRuntime(1772): Caused by: java.lang.NullPointerException
10-07 16:57:47.586: E/AndroidRuntime(1772): at android.content.ContextWrapper.getCacheDir(ContextWrapper.java:200)
10-07 16:57:47.586: E/AndroidRuntime(1772): at com.gettford.community.FileCache.<init>(FileCache.java:18)
10-07 16:57:47.586: E/AndroidRuntime(1772): at com.gettford.community.ImageLoader.<init>(ImageLoader.java:35)
10-07 16:57:47.586: E/AndroidRuntime(1772): at com.gettford.community.SingleItemView.<init>(SingleItemView.java:15)
10-07 16:57:47.586: E/AndroidRuntime(1772): at java.lang.Class.newInstanceImpl(Native Method)
10-07 16:57:47.586: E/AndroidRuntime(1772): at java.lang.Class.newInstance(Class.java:1319)
10-07 16:57:47.586: E/AndroidRuntime(1772): at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
10-07 16:57:47.586: E/AndroidRuntime(1772): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
10-07 16:57:47.586: E/AndroidRuntime(1772): ... 11 more
如果我删除 SingleItemView 上的行以显示图像就像一个魅力。
提前致谢。