我能够运行我的程序，但是一旦我进入这个活动，应用程序崩溃，我不知道为什么，我的想法，我真的很感激任何帮助！非常感谢你！
package com.malthorn.zenstatemeditation;
import java.io.File;
import java.io.FilenameFilter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
import android.app.ListActivity;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.CountDownTimer;
import android.os.Environment;
import android.os.Handler;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
class Mp3Filter implements FilenameFilter {
@Override
public boolean accept(File dir, String filename) {
return (filename.startsWith("Zen"));
}
}
public class MeditateScreen extends ListActivity {
private static final String SD_PATH = new String("/sdcard/");
private List<String> songs = new ArrayList<String>();
private MediaPlayer mp = new MediaPlayer();
String[] times = new String[]{"3 minutes", "5 minutes", "10 minutes", "20 minutes"};
TextView timerValue = (TextView) findViewById(R.id.timerValue);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_meditate_screen);
updatePlaylist();
updateTimeList();
}
public void stopMusic(View view) {
mp.stop();
}
public void onItemClick(AdapterView<?> a, View v, int position, long id) {
if( v.getId() == R.id.songList1 )
{
try {
mp.reset();
mp.setDataSource(SD_PATH + songs.get(position));
mp.prepare();
mp.start();
} catch (IOException e) {
Log.v(getString(R.string.app_name), e.getMessage());
}
}
else if( v.getId() == R.id.timeList1 )
{
// String[] times = new String[]{"3 minutes", "5 minutes", "10 minutes", "20 minutes"};
if(position == 0) {
new CountDownTimer(180000, 1000) {
public void onTick(long millisUntilFinished) {
timerValue.setText("time remaining: " + millisUntilFinished / 1000);
}
public void onFinish() {
timerValue.setText("Session finished!");
}
}.start();
} else if(position == 1) {
new CountDownTimer(300000, 1000) {
public void onTick(long millisUntilFinished) {
timerValue.setText("time remaining: " + millisUntilFinished / 1000);
}
public void onFinish() {
timerValue.setText("Session finished!");
}
}.start();
} else if(position == 2) {
new CountDownTimer(600000, 1000) {
public void onTick(long millisUntilFinished) {
timerValue.setText("time remaining: " + millisUntilFinished / 1000);
}
public void onFinish() {
timerValue.setText("Session finished!");
}
}.start();
} else if(position == 3) {
new CountDownTimer(1200000, 1000) {
public void onTick(long millisUntilFinished) {
timerValue.setText("time remaining: " + millisUntilFinished / 1000);
}
public void onFinish() {
timerValue.setText("Session finished!");
}
}.start();
}
}
}
public void pauseResume(View view) {
Button pauseResume = (Button) findViewById(R.id.bPauseResume);
if(mp.isPlaying()){
mp.pause();
pauseResume.setText("Resume");
} else {
mp.start();
pauseResume.setText("Pause");
}
}
public void updatePlaylist() {
File extStore = Environment.getExternalStorageDirectory();
File home = new File(extStore.getAbsolutePath() + "/music/");
if (home.listFiles(new Mp3Filter()).length > 0) {
for (File file : home.listFiles(new Mp3Filter())) {
songs.add(file.getName());
}
ArrayAdapter<String> songList = new ArrayAdapter<String>(this,
R.layout.song_item, songs);
setListAdapter(songList);
}
}
public void updateTimeList() {
ArrayAdapter<String> timeList = new ArrayAdapter<String>(this,
R.layout.song_item, times);
setListAdapter(timeList);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.meditate_screen, menu);
return true;
}
}
我的XML格式：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MeditateScreen" >
<ListView
android:id="@+id/songList1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="@+id/bStop"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true" >
</ListView>
<Button
android:id="@+id/bStop"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="stopMusic"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:text="Stop Music" />
<Button
android:id="@+id/bPauseResume"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/bStop"
android:layout_alignBottom="@+id/bStop"
android:onClick="pauseResume"
android:layout_alignRight="@id/songList1"
android:layout_marginRight="47dp"
android:text="Pause/Resume" />
<Button
android:id="@+id/bTimer"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/bStop"
android:layout_below="@+id/bStop"
android:layout_marginTop="20dp"
android:onClick="startTimer"
android:text="Start Timer" />
<TextView
android:id="@+id/timerValue"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/bTimer"
android:layout_alignBottom="@+id/bTimer"
android:layout_alignRight="@+id/bPauseResume"
android:layout_marginRight="22dp"
android:text="0:00" />
<ListView
android:id="@+id/timeList1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/bTimer"
android:layout_below="@+id/bTimer" >
</ListView>
</RelativeLayout>
我的LogCat错误：
01-29 01:56:27.626: E/AndroidRuntime(1105): FATAL EXCEPTION: main
01-29 01:56:27.626: E/AndroidRuntime(1105): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.malthorn.zenstatemeditation/com.malthorn.zenstatemeditation.MeditateScreen}: java.lang.NullPointerException
01-29 01:56:27.626: E/AndroidRuntime(1105): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137)
01-29 01:56:27.626: E/AndroidRuntime(1105): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
01-29 01:56:27.626: E/AndroidRuntime(1105): at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-29 01:56:27.626: E/AndroidRuntime(1105): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
01-29 01:56:27.626: E/AndroidRuntime(1105): at android.os.Handler.dispatchMessage(Handler.java:99)
01-29 01:56:27.626: E/AndroidRuntime(1105): at android.os.Looper.loop(Looper.java:137)
01-29 01:56:27.626: E/AndroidRuntime(1105): at android.app.ActivityThread.main(ActivityThread.java:5103)
01-29 01:56:27.626: E/AndroidRuntime(1105): at java.lang.reflect.Method.invokeNative(Native Method)
01-29 01:56:27.626: E/AndroidRuntime(1105): at java.lang.reflect.Method.invoke(Method.java:525)
01-29 01:56:27.626: E/AndroidRuntime(1105): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
01-29 01:56:27.626: E/AndroidRuntime(1105): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-29 01:56:27.626: E/AndroidRuntime(1105): at dalvik.system.NativeStart.main(Native Method)
01-29 01:56:27.626: E/AndroidRuntime(1105): Caused by: java.lang.NullPointerException
01-29 01:56:27.626: E/AndroidRuntime(1105): at android.app.Activity.findViewById(Activity.java:1853)
01-29 01:56:27.626: E/AndroidRuntime(1105): at com.malthorn.zenstatemeditation.MeditateScreen.<init>(MeditateScreen.java:41)
01-29 01:56:27.626: E/AndroidRuntime(1105): at java.lang.Class.newInstanceImpl(Native Method)
01-29 01:56:27.626: E/AndroidRuntime(1105): at java.lang.Class.newInstance(Class.java:1130)
01-29 01:56:27.626: E/AndroidRuntime(1105): at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
01-29 01:56:27.626: E/AndroidRuntime(1105): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128)
01-29 01:56:27.626: E/AndroidRuntime(1105): ... 11 more
答案 0 :(得分：0)
setContentView（R.layout.activity_meditate_screen）之后; 您必须定义您在活动中使用的所有视图。
在设定值之前 -
timerValue.setText(YOUR VALUE);
使用
TextView = findViewById(R.id.timerValue);
希望这项工作......
答案 1 :(得分：0)
有3点可能导致崩溃
1）如果您使用ListActivity，则需要至少有ListView个@android:id/list，否则如果您尝试setListAdapter该应用将会崩溃。
2）如果您的SD卡中没有名为music的文件夹，那么
File extStore = Environment.getExternalStorageDirectory();
File home = new File(extStore.getAbsolutePath() + "/music/");
if (home.listFiles(new Mp3Filter()).length > 0)
将使应用程序崩溃，因为它无法找到文件路径
3）你做不到
TextView timerValue = (TextView) findViewById(R.id.timerValue);
在致电setContentView之前。在onCreate
setContentView内