Android抛出空指针异常
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21-12-2019 - |
题
我正在尝试从音频目录中获取音频文件,为此我使用下面的代码。我不明白为什么会出现这种情况 if (home.listFiles(new FileExtensionFilter()).length > 0)
正在抛出一个错误。代码如下。
Uri allsongsuri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
final String MEDIA_PATH = allsongsuri.toString();
private ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
public ArrayList<HashMap<String, String>> getPlayList(){
System.out.println(" -- "+MEDIA_PATH);
File home = new File(MEDIA_PATH);
if (home.listFiles(new FileExtensionFilter()).length > 0) {
for (File file : home.listFiles(new FileExtensionFilter())) {
HashMap<String, String> song = new HashMap<String, String>();
song.put("songTitle", file.getName().substring(0, (file.getName().length() - 4)));
song.put("songPath", file.getPath());
// Adding each song to SongList
songsList.add(song);
}
}
return songsList;
}
class FileExtensionFilter implements FilenameFilter {
public boolean accept(File dir, String name) {
return (name.endsWith(".mp3") || name.endsWith(".MP3"));
}
我需要使用 hashMap 将音频文件存储在 ArrayList 中。我尝试这个示例将文件存储在列表中 http://android-er.blogspot.in/2012/02/list-audio-media-in-mediastoreaudiomedi.html 。使用这个示例,我尝试了很多将列表存储在 ArrayList 中,因为我的需求需要这样做。但没有成功。我需要帮助。我必须将音频文件存储在 Arraylist 中。
解决方案 3
public class SongsManager {
final String MEDIA_PATH = Environment.getExternalStorageDirectory()
.getPath() + "/";
private ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
private String mp3Pattern = ".mp3";
// Constructor
public SongsManager() {
}
/**
* Function to read all mp3 files and store the details in
* ArrayList
* */
public ArrayList<HashMap<String, String>> getPlayList() {
System.out.println(MEDIA_PATH);
if (MEDIA_PATH != null) {
File home = new File(MEDIA_PATH);
File[] listFiles = home.listFiles();
if (listFiles != null && listFiles.length > 0) {
for (File file : listFiles) {
System.out.println(file.getAbsolutePath());
if (file.isDirectory()) {
scanDirectory(file);
} else {
addSongToList(file);
}
}
}
}
// return songs list array
return songsList;
}
private void scanDirectory(File directory) {
if (directory != null) {
File[] listFiles = directory.listFiles();
if (listFiles != null && listFiles.length > 0) {
for (File file : listFiles) {
if (file.isDirectory()) {
scanDirectory(file);
} else {
addSongToList(file);
}
}
}
}
}
private void addSongToList(File song) {
if (song.getName().endsWith(mp3Pattern)) {
HashMap<String, String> songMap = new HashMap<String, String>();
songMap.put("songTitle",
song.getName().substring(0, (song.getName().length() - 4)));
songMap.put("songPath", song.getPath());
// Adding each song to SongList
songsList.add(songMap);
}
}
}
. 其他提示
这必须是 home.listFiles
返回 null
.
从 Android 开发者参考 在 public File[] listFiles (FileFilter filter)
获取此文件表示的目录中的文件列表。然后通过 FileFilter 过滤此列表,并将匹配的文件作为文件数组返回。 如果该文件不是目录,则返回 null。 如果过滤器为空,则所有文件都匹配。
所以你需要确保 MEDIA_PATH
是一个正确的目录。
“listfiles()”方法如果找不到文件,则可以返回null。我建议在检查它是否首先是null,并且只有在null以外的东西时才继续。示例:
public ArrayList<HashMap<String, String>> getPlayList(){
System.out.println(" -- "+MEDIA_PATH);
File home = new File(MEDIA_PATH);
if (home.listFiles(new FileExtensionFilter()) != null){
if (home.listFiles(new FileExtensionFilter()).length > 0) {
for (File file : home.listFiles(new FileExtensionFilter())) {
HashMap<String, String> song = new HashMap<String, String>();
song.put("songTitle", file.getName().substring(0, (file.getName().length() - 4)));
song.put("songPath", file.getPath());
// Adding each song to SongList
songsList.add(song);
}
}
}
return songsList;
}
.
您可能希望放入别的语句,以确保在返回时ony songslist不是null。
与Ref to Anup和Dartom的答案我只想要将代码与文件名过滤器
汇总 public class SongsManager {
// SDCard Path
// final String MEDIA_PATH = new String("/sdcard/sound_recorder");
final String MEDIA_PATH =Environment.getExternalStorageDirectory()+"/sound_recorder";
private ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
// Constructor
public SongsManager(){
}
/**
* Function to read all mp3 files from sdcard
* and store the details in ArrayList
* */
public ArrayList<HashMap<String, String>> getPlayList(){
Log.d("testsd",MEDIA_PATH);
File home = new File(MEDIA_PATH);
// if (home.listFiles(new FileExtensionFilter()).length > 0) //don't use this to avoid null pointer exception !
if (home.listFiles(new FileExtensionFilter())!=null) {
for (File file : home.listFiles(new FileExtensionFilter())) {
HashMap<String, String> song = new HashMap<String, String>();
song.put("songTitle", file.getName().substring(0, (file.getName().length() - 4)));
song.put("songPath", file.getPath());
// Adding each song to SongList
songsList.add(song);
}
}
// return songs list array
return songsList;
}
/**
* Class to filter files which are having .mp3 extension
* */
class FileExtensionFilter implements FilenameFilter {
public boolean accept(File dir, String name) {
return (name.endsWith(".mp3") || name.endsWith(".MP3") || name.endsWith(".3gpp") || name.endsWith(".wav")); //add more extensions here
}
}
}
. 谢谢一句话.....没有SDCARD的MOTO G.它效仿物理SDCARD ......仍然不起作用。
但您的代码与具有物理SDCARD的另一个摩托罗拉合作完美
我的意思是当sdcard是仿真notwork ..i尝试所有的media_paths
我需要你的建议......谢谢。 // final string media_path= neverional.getexternalstoragedirectory()。getPath()+“/”; //私有最终字符串Media_path= new字符串(“/ sdcard / res / Raw /”); // final string media_path= neverional.getexternalstoragedirectory()。getabsolutepath()+“/”; // final string media_path= new字符串(“/ sdcard /”); // final string media_path= neverional.getexternalstoragedirectory()。getPath()+“/”; // final string media_path=“”; // final string media_path= new字符串(“/ sdcard / musica /”); // final string media_path= neverional.getexternalstoragedirectory()。getPath()+“/”; //最终字符串MediaPath= Environment.getExternalStoragedirectory()。getabsolutepath()+“/ musica /”; //最终字符串MediaPath= new字符串(“/ sdcard /”); // final string media_path= neverional.getexternalstoragedirectory()。getPath()+“/”; 最终字符串Media_path= Environment.getExternalStoragedIrectory()。getabsolutepath()+“/”;
确保不要忘记Manifest.xml中的使用权限读取外部存储