所以我的Android Gallery中有3个文件夹。我试图将这些文件夹的文件读入File数组，然后从那里将图像源转换为实际的ImageViews。
我的问题是引用文件数组时出现NullPointerException的问题。这是一些代码：
// Get image files paths.
private File topsFolder = new File(Environment.getExternalStorageDirectory().getPath() + "/DressIt Tops/");
private File bottomsFolder = new File(Environment.getExternalStorageDirectory()
.getPath() + "/DressIt Bottoms/");
private File shoesFolder = new File(Environment.getExternalStorageDirectory()
.getPath() + "/DressIt Shoes/");
private File[] allTops = topsFolder.listFiles();
private File[] allBottoms = bottomsFolder.listFiles();
private File[] allShoes = shoesFolder.listFiles();
使用这些图像文件数组...
ImageAdapter topAdapter = new ImageAdapter(createList(allTops));
topList.setAdapter(topAdapter);
ImageAdapter midAdapter = new ImageAdapter(createList(allBottoms));
midList.setAdapter(midAdapter);
ImageAdapter botAdapter = new ImageAdapter(createList(allShoes));
botList.setAdapter(botAdapter);
我的CreateList方法。错误是当我引用list.length时。
private List<ImageClass> createList(File[] list) {
List<ImageClass> result = new ArrayList<ImageClass>();
ImageClass img;
Bitmap bmp;
if (list.length > 0) {
for (int i = 0; i < list.length; i++) {
bmp = BitmapFactory.decodeFile(list[i].getAbsolutePath());
img = new ImageClass(bmp);
result.add(img);
}
} else
result.add(new ImageClass(this.getResources().getIdentifier(
"no_imgs_yet", "drawable", this.getPackageName())));
return result;
}
就像我说的那样，错误是当我使用list.length引用一个File数组时，例如我在第一个代码段中创建的allTops。
这是LogCat错误消息：
05-05 19:43:49.409: D/dalvikvm(537): Not late-enabling CheckJNI (already on)
05-05 19:43:51.069: D/dalvikvm(537): GC_FOR_ALLOC freed 70K, 3% free 10185K/10439K, paused 63ms
05-05 19:43:51.079: I/dalvikvm-heap(537): Grow heap (frag case) to 10.566MB for 562516-byte allocation
05-05 19:43:51.139: D/dalvikvm(537): GC_CONCURRENT freed 1K, 3% free 10733K/11015K, paused 6ms+7ms
05-05 19:43:51.278: D/com.example.dressit(537): /mnt/sdcard/DressIt Tops
05-05 19:43:51.289: D/AndroidRuntime(537): Shutting down VM
05-05 19:43:51.289: W/dalvikvm(537): threadid=1: thread exiting with uncaught exception (group=0x409961f8)
05-05 19:43:51.319: E/AndroidRuntime(537): FATAL EXCEPTION: main
05-05 19:43:51.319: E/AndroidRuntime(537): java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.example.dressit/com.example.dressit.MainActivity}: java.lang.NullPointerException
05-05 19:43:51.319: E/AndroidRuntime(537): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
05-05 19:43:51.319: E/AndroidRuntime(537): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
05-05 19:43:51.319: E/AndroidRuntime(537): at android.app.ActivityThread.access$600(ActivityThread.java:122)
05-05 19:43:51.319: E/AndroidRuntime(537): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
05-05 19:43:51.319: E/AndroidRuntime(537): at android.os.Handler.dispatchMessage(Handler.java:99)
05-05 19:43:51.319: E/AndroidRuntime(537): at android.os.Looper.loop(Looper.java:137)
05-05 19:43:51.319: E/AndroidRuntime(537): at android.app.ActivityThread.main(ActivityThread.java:4340)
05-05 19:43:51.319: E/AndroidRuntime(537): at java.lang.reflect.Method.invokeNative(Native Method)
05-05 19:43:51.319: E/AndroidRuntime(537): at java.lang.reflect.Method.invoke(Method.java:511)
05-05 19:43:51.319: E/AndroidRuntime(537): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-05 19:43:51.319: E/AndroidRuntime(537): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-05 19:43:51.319: E/AndroidRuntime(537): at dalvik.system.NativeStart.main(Native Method)
05-05 19:43:51.319: E/AndroidRuntime(537): Caused by: java.lang.NullPointerException
05-05 19:43:51.319: E/AndroidRuntime(537): at com.example.dressit.MainActivity.createList(MainActivity.java:125)
05-05 19:43:51.319: E/AndroidRuntime(537): at com.example.dressit.MainActivity.onCreate(MainActivity.java:103)
05-05 19:43:51.319: E/AndroidRuntime(537): at android.app.Activity.performCreate(Activity.java:4465)
05-05 19:43:51.319: E/AndroidRuntime(537): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
05-05 19:43:51.319: E/AndroidRuntime(537): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
05-05 19:43:51.319: E/AndroidRuntime(537): ... 11 more
05-05 19:43:51.509: D/dalvikvm(537): GC_CONCURRENT freed 420K, 5% free 10747K/11271K, paused 6ms+5ms
05-05 19:44:25.629: I/Process(537): Sending signal. PID: 537 SIG: 9
我也有我的同意：
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
很抱歉投入了这么多代码，但我觉得有人在这里弄清楚这个问题是必要且足够的。
我现在已经花了几个小时，以为我会问社区！非常感谢大家。
编辑：感谢所有的反馈！这是我的代码，用于保存拍摄的图像。这应该显示所有已保存图像的路径。另外，我的LogCat说文件路径为/ mnt / sdcard / DressIt Tops。
/** Create a File for saving an image or video */
private static File getOutputMediaFile(int type) {
// To be safe, you should check that the SDCard is mounted
// using Environment.getExternalStorageState() before doing this.
String dirName;
if (imageType == 1) {
dirName = "DressIt Tops";
} else if (imageType == 2) {
dirName = "DressIt Bottoms";
} else
dirName = "DressIt Shoes";
File mediaStorageDir = new File(
Environment
.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),
dirName);
// This location works best if you want the created images to be shared
// between applications and persist after your app has been uninstalled.
// Create the storage directory if it does not exist
if (!mediaStorageDir.exists()) {
if (!mediaStorageDir.mkdirs()) {
Log.d(dirName, "failed to create directory");
return null;
}
}
// Create a media file name
String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss")
.format(new Date());
File mediaFile;
if (type == MEDIA_TYPE_IMAGE) {
mediaFile = new File(mediaStorageDir.getPath() + File.separator
+ "IMG_" + timeStamp + ".jpg");
} else if (type == MEDIA_TYPE_VIDEO) {
mediaFile = new File(mediaStorageDir.getPath() + File.separator
+ "VID_" + timeStamp + ".mp4");
} else {
return null;
}
return mediaFile;
}
最佳答案
根据File.listFiles()的文档，如果null不是目录，它将返回File。
关于为什么会这样，有三种（非常相似的）替代方案...
由（例如）... String返回的Environment.getExternalStorageDirectory().getPath() + "/DressIt Tops/"代表无效目录（..."/DressIt Bottoms/"和/或..."/DressIt Shoes/"可能相同）。
返回的Strings是有效路径，但其中一个或另一个是文件，而不是目录。
目录确实存在，但是您输入的目录名称有错字-记住文件系统区分大小写。如果您将“ / DressIt Tops /”目录创建为“” / dressIt tops /”（例如），则找不到有效路径。
还有一件事-永远不要假设任何路径到Android文件系统上的任何地方-记录Environment.getExternalStorageDirectory().getPath()实际返回的内容，检查它是否是您创建目录的位置，并检查所有文件的大小写是否正确。