Android:如何访问音频文件？
Android:如何访问音频文件？
提问于 2012-10-29 14:15:18
在我的应用程序中，我使用这个方法来访问音频文件：
public Cursor pobierzPlikiAudio(){
String[] STAR = {"*"};
String selection = MediaStore.Audio.Media.IS_MUSIC + " != 0";
Uri uri= Uri.parse("content://pl/aplikacja/app/provider/MediaStore/Audio");
return getContentResolver().query(uri, STAR, selection, null, null);
}但在我的LogCat中，我得到了一个nullPointerException。怎么啦？
出现错误的Logcat：
10-29 07:04:17.729: E/AndroidRuntime(24354): FATAL EXCEPTION: main
10-29 07:04:17.729: E/AndroidRuntime(24354): java.lang.RuntimeException: Unable to start activity ComponentInfo{pl.aplikacja.app/pl.aplikacja.app.MainActivity}: java.lang.NullPointerException
10-29 07:04:17.729: E/AndroidRuntime(24354): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
10-29 07:04:17.729: E/AndroidRuntime(24354): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
10-29 07:04:17.729: E/AndroidRuntime(24354): at android.app.ActivityThread.access$600(ActivityThread.java:127)
10-29 07:04:17.729: E/AndroidRuntime(24354): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
10-29 07:04:17.729: E/AndroidRuntime(24354): at android.os.Handler.dispatchMessage(Handler.java:99)
10-29 07:04:17.729: E/AndroidRuntime(24354): at android.os.Looper.loop(Looper.java:137)
10-29 07:04:17.729: E/AndroidRuntime(24354): at android.app.ActivityThread.main(ActivityThread.java:4441)
10-29 07:04:17.729: E/AndroidRuntime(24354): at java.lang.reflect.Method.invokeNative(Native Method)
10-29 07:04:17.729: E/AndroidRuntime(24354): at java.lang.reflect.Method.invoke(Method.java:511)
10-29 07:04:17.729: E/AndroidRuntime(24354): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
10-29 07:04:17.729: E/AndroidRuntime(24354): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
10-29 07:04:17.729: E/AndroidRuntime(24354): at dalvik.system.NativeStart.main(Native Method)
10-29 07:04:17.729: E/AndroidRuntime(24354): Caused by: java.lang.NullPointerException
10-29 07:04:17.729: E/AndroidRuntime(24354): at pl.aplikacja.app.MainActivity.onCreate(MainActivity.java:18)
10-29 07:04:17.729: E/AndroidRuntime(24354): at android.app.Activity.performCreate(Activity.java:4465)
10-29 07:04:17.729: E/AndroidRuntime(24354): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
10-29 07:04:17.729: E/AndroidRuntime(24354): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
10-29 07:04:17.729: E/AndroidRuntime(24354): ... 11 more这是MainActivity.java
package pl.aplikacja.app;
import android.os.Bundle;
import android.database.Cursor;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;
import android.provider.MediaStore;
public class MainActivity extends Activity {
private Dostawca dostawca;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Cursor tablicaPlikow = dostawca.pobierzPlikiAudio();
if (tablicaPlikow.moveToFirst()) {
String title;
String artist;
String album;
int titleColumn = tablicaPlikow.getColumnIndex(MediaStore.EXTRA_MEDIA_TITLE);
int artistColumn = tablicaPlikow.getColumnIndex(MediaStore.EXTRA_MEDIA_ARTIST);
int albumColumn =tablicaPlikow.getColumnIndex(MediaStore.EXTRA_MEDIA_ALBUM);
// Get the field values
title = tablicaPlikow.getString(titleColumn);
artist = tablicaPlikow.getString(artistColumn);
album = tablicaPlikow.getString(albumColumn);
TextView widok = (TextView) findViewById(R.id.tekst);
widok.setText(""+title+" "+ artist + " " + album);
}
setContentView(R.layout.activity_main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}回答 5
Stack Overflow用户
发布于 2012-10-29 14:32:42
我想你把uri放错了。在这个Uri上，没有媒体文件，这就是为什么你会得到空指针异常。点击下面的链接
GetMedia Information
Stack Overflow用户
发布于 2012-10-29 14:43:56
下面是一些获取所有音频并以列表格式显示的代码。
mAdapter = new SimpleCursorAdapter(
this,
// Use a template that displays a text view
R.layout.media_select_row,
// Give the cursor to the list adatper
createCursor(""),
// Map from database columns...
new String[] {
MediaStore.Audio.Media.ARTIST,
MediaStore.Audio.Media.ALBUM,
//MediaStore.Audio.Media.DATE_ADDED,
MediaStore.Audio.Media.TITLE,
MediaStore.Audio.Media._ID,
MediaStore.Audio.Media._ID},
// To widget ids in the row layout...
new int[] {
R.id.row_artist,
R.id.row_album,
R.id.row_title,
R.id.row_icon,
R.id.row_options_button});
setListAdapter(mAdapter);
getListView().setItemsCanFocus(true);
// Normal click - open the editor
getListView().setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView parent,
View view,
int position,
long id) {
DoWhatYouWant();
}
});
} catch (SecurityException e) {
// No permission to retrieve audio?
Log.e("RecordingApp", e.toString());
// todo error 1
} catch (IllegalArgumentException e) {
// No permission to retrieve audio?
Log.e("RecordingApp", e.toString());
// todo error 2这段代码和我一起工作..如果你有任何问题，请随时提问。
Stack Overflow用户
发布于 2012-10-29 15:51:19
查看变量dostawca，它看起来没有初始化。这就是为什么你会得到空指针的原因，除了Cursor tablicaPlikow = dostawca.pobierzPlikiAudio();这一行
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/13116708
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