我在listview中制作带有歌词的媒体播放应用程序，随着媒体的进展，列表视图滚动，现在我希望当前的播放节目在列表视图中以不同的颜色突出显示。所以我在处理程序中使用以下代码，但是我得到了一个NPE。
if(mediaPlayer.getCurrentPosition()/1000 > 0 && mediaPlayer.getCurrentPosition()/1000 < 20){
listView.smoothScrollToPosition(3);
View element = listView.getChildAt(3);
element.setBackgroundColor(0xff0000ff);
完整代码
public class MainActivity extends Activity {
TextView T,S1;
MediaPlayer mediaPlayer;
ScrollView sv;
SeekBar seek_bar;
boolean lang = true;
Typeface tf;
String [] LyricsE;
String [] LyricsH;
ListView listView;
Button b;
private ArrayAdapter dataAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//mediaPlayer = MediaPlayer.create(MainActivity.this, R.raw.stair);
//mediaPlayer.start();
LyricsE = new String [] {"","","",getResources().getString(R.string.V1E),getResources().getString(R.string.V2E),
getResources().getString(R.string.V3E),
getResources().getString(R.string.V4E),getResources().getString(R.string.V4E),getResources().getString(R.string.V5E),
getResources().getString(R.string.V6E),getResources().getString(R.string.V7E),getResources().getString(R.string.V8E),
getResources().getString(R.string.V9E),getResources().getString(R.string.V10E),getResources().getString(R.string.V11E),
getResources().getString(R.string.V12E),getResources().getString(R.string.V13E),getResources().getString(R.string.V14E),
getResources().getString(R.string.V15E),getResources().getString(R.string.V16E),getResources().getString(R.string.V17E),
getResources().getString(R.string.V18E),getResources().getString(R.string.V19E),getResources().getString(R.string.V20E),
getResources().getString(R.string.V21E),getResources().getString(R.string.V22E),getResources().getString(R.string.V23E),
getResources().getString(R.string.V24E),getResources().getString(R.string.V25E),getResources().getString(R.string.V26E),
getResources().getString(R.string.V27E),getResources().getString(R.string.V28E),getResources().getString(R.string.V29E),
getResources().getString(R.string.V30E),getResources().getString(R.string.V31E),getResources().getString(R.string.V32E),
getResources().getString(R.string.V33E),getResources().getString(R.string.V34E),getResources().getString(R.string.V35E),
getResources().getString(R.string.V36E),getResources().getString(R.string.V37E),getResources().getString(R.string.V38E),
getResources().getString(R.string.V39E),getResources().getString(R.string.V40E),getResources().getString(R.string.V41E),
getResources().getString(R.string.V42E)};
LyricsH = new String[] {"","","",getResources().getString(R.string.V1H),getResources().getString(R.string.V2H),
getResources().getString(R.string.V3H),
getResources().getString(R.string.V4H),getResources().getString(R.string.V4H),getResources().getString(R.string.V5H),
getResources().getString(R.string.V6H),getResources().getString(R.string.V7H),getResources().getString(R.string.V8H),
getResources().getString(R.string.V9H),getResources().getString(R.string.V10H),getResources().getString(R.string.V11H),
getResources().getString(R.string.V12H),getResources().getString(R.string.V13H),getResources().getString(R.string.V14H),
getResources().getString(R.string.V15H),getResources().getString(R.string.V16H),getResources().getString(R.string.V17H),
getResources().getString(R.string.V18H),getResources().getString(R.string.V19H),getResources().getString(R.string.V20H),
getResources().getString(R.string.V21H),getResources().getString(R.string.V22H),getResources().getString(R.string.V23H),
getResources().getString(R.string.V24H),getResources().getString(R.string.V25H),getResources().getString(R.string.V26H),
getResources().getString(R.string.V27H),getResources().getString(R.string.V28H),getResources().getString(R.string.V29H),
getResources().getString(R.string.V30H),getResources().getString(R.string.V31H),getResources().getString(R.string.V32H),
getResources().getString(R.string.V33H),getResources().getString(R.string.V34H),getResources().getString(R.string.V35H),
getResources().getString(R.string.V36H),getResources().getString(R.string.V37H),getResources().getString(R.string.V38H),
getResources().getString(R.string.V39H),getResources().getString(R.string.V40H),getResources().getString(R.string.V41H),
getResources().getString(R.string.V42H)};
String fontPath = "fonts/DroidSansDevanagari-Regular.ttf";
tf = Typeface.createFromAsset(getAssets(), fontPath);
mediaPlayer = MediaPlayer.create(MainActivity.this, R.raw.stair);
b = (Button)findViewById(R.id.button1);
Button L = (Button)findViewById(R.id.button2);
L.setOnClickListener(Lang);
b.setOnClickListener(on);
T = (TextView)findViewById(R.id.textView1);
S1 = (TextView)findViewById(R.id.textView2);
seek_bar =(SeekBar)findViewById(R.id.seekBar1);
listView = (ListView) findViewById(R.id.listView1);
if(lang){
//ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.list,R.id.textView2, LyricsE);
//listView.setAdapter(adapter);
dataAdapter = new arrayAdapter(MainActivity.this, LyricsE);
listView.setAdapter(dataAdapter);
}
if(!lang){
//ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.list,R.id.textView2, LyricsH);
//listView.setAdapter(adapter);
dataAdapter = new arrayAdapter(MainActivity.this, LyricsH);
listView.setAdapter(dataAdapter);
}
}
private View.OnClickListener on = new View.OnClickListener() {
@Override
public void onClick(View v) {
boolean flag = true;
int B = 0;
// mediaPlayer = MediaPlayer.create(MainActivity.this, R.raw.stair);
if(mediaPlayer.isPlaying()){
mediaPlayer.pause();
B = mediaPlayer.getCurrentPosition();
flag = false;
b.setText("Play");
System.out.println("in is.playing");
}else if(!flag && !mediaPlayer.isPlaying()){
mediaPlayer.seekTo(B);
b.setText("Pause");
System.out.println("in flag and !playing");
}
else{
b.setText("Pause");
System.out.println("Normal execution");
//listView = (ListView) findViewById(R.id.listView1);
// mediaPlayer = MediaPlayer.create(MainActivity.this, R.raw.stair);
mediaPlayer.start();
seek_bar.setMax(mediaPlayer.getDuration());
seek_bar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
}
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
}
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
if(mediaPlayer != null && fromUser){
mediaPlayer.seekTo(progress);
}
}
});
final Handler handler = new Handler();
handler.post(new Runnable(){
@Override
public void run(){
int X = mediaPlayer.getCurrentPosition();
S1.setText(""+X);
setProgressText();
seek_bar.setProgress(mediaPlayer.getCurrentPosition());
if(mediaPlayer.getCurrentPosition()/1000 > 0 && mediaPlayer.getCurrentPosition()/1000 < 20){
//listView.smoothScrollToPosition(3);
//View element = listView.getChildAt(3);
//element.setBackgroundColor(Color.YELLOW);
System.out.println("FIrst if");
int wantedPosition = 3;
int firstPosition = listView.getFirstVisiblePosition() - listView.getHeaderViewsCount(); // This is the same as child #0
int wantedChild = wantedPosition - firstPosition;
// Say, first visible position is 8, you want position 10, wantedChild will now be 2
// So that means your view is child #2 in the ViewGroup:
if (wantedChild < 0 || wantedChild >= listView.getChildCount()) {
System.out.println( "Unable to get view for desired position, because it's not being displayed on screen.");
return;
}
listView.smoothScrollToPosition(wantedChild);
View wantedView = listView.getChildAt(wantedChild);
wantedView.setBackgroundColor(Color.YELLOW);
}else if(mediaPlayer.getCurrentPosition()/1000 > 20 && mediaPlayer.getCurrentPosition()/1000 < 54){
// listView.smoothScrollToPosition(4);
// View element = listView.getChildAt(4);
// element.setBackgroundColor(Color.YELLOW);
System.out.println("2 if");
int wantedPosition = 4;
int firstPosition = listView.getFirstVisiblePosition() - listView.getHeaderViewsCount(); // This is the same as child #0
int wantedChild = wantedPosition - firstPosition;
// Say, first visible position is 8, you want position 10, wantedChild will now be 2
// So that means your view is child #2 in the ViewGroup:
if (wantedChild < 0 || wantedChild >= listView.getChildCount()) {
System.out.println( "Unable to get view for desired position, because it's not being displayed on screen.");
return;
}
listView.smoothScrollToPosition(wantedChild);
View wantedView = listView.getChildAt(wantedChild);
wantedView.setBackgroundColor(Color.YELLOW);
}else if(mediaPlayer.getCurrentPosition()/1000 > 54 && mediaPlayer.getCurrentPosition()/1000 < 67){
//listView.smoothScrollToPosition(5);
//View element = listView.getChildAt(5);
//element.setBackgroundColor(Color.YELLOW);
System.out.println("3 if");
int wantedPosition = 5;
int firstPosition = listView.getFirstVisiblePosition() - listView.getHeaderViewsCount(); // This is the same as child #0
int wantedChild = wantedPosition - firstPosition;
// Say, first visible position is 8, you want position 10, wantedChild will now be 2
// So that means your view is child #2 in the ViewGroup:
if (wantedChild < 0 || wantedChild >= listView.getChildCount()) {
System.out.println( "Unable to get view for desired position, because it's not being displayed on screen.");
return;
}
listView.smoothScrollToPosition(wantedChild);
View wantedView = listView.getChildAt(wantedChild);
wantedView.setBackgroundColor(Color.YELLOW);
}else if(mediaPlayer.getCurrentPosition()/1000 > 67 && mediaPlayer.getCurrentPosition()/1000 < 75){
listView.smoothScrollToPosition(6);
System.out.println("4 if");
}else if(mediaPlayer.getCurrentPosition()/1000 > 20 && mediaPlayer.getCurrentPosition()/1000 < 54){
listView.smoothScrollToPosition(7);
System.out.println("5 if");
}else if(mediaPlayer.getCurrentPosition()/1000 > 20 && mediaPlayer.getCurrentPosition()/1000 < 54){
listView.smoothScrollToPosition(8);
System.out.println("6 if");
}else if(mediaPlayer.getCurrentPosition()/1000 > 20 && mediaPlayer.getCurrentPosition()/1000 < 54){
listView.smoothScrollToPosition(9);
System.out.println("7 if");
}else if(mediaPlayer.getCurrentPosition()/1000 > 20 && mediaPlayer.getCurrentPosition()/1000 < 54){
}
handler.postDelayed(this, 1000L);
}
});
}
}
};
protected void setProgressText() {
String X ;
final int HOUR = 60*60*1000;
final int MINUTE = 60*1000;
final int SECOND = 1000;
int durationInMillis = mediaPlayer.getDuration();
int curVolume = mediaPlayer.getCurrentPosition();
int durationHour = durationInMillis/HOUR;
int durationMint = (durationInMillis%HOUR)/MINUTE;
int durationSec = (durationInMillis%MINUTE)/SECOND;
int currentHour = curVolume/HOUR;
int currentMint = (curVolume%HOUR)/MINUTE;
int currentSec = (curVolume%MINUTE)/SECOND;
if(durationHour>0){
X = (""+String.format("%02d:%02d:%02d/%02d:%02d:%02d",
currentHour,currentMint,currentSec, durationHour,durationMint,durationSec));
}else{
X = (""+String.format("%02d:%02d/%02d:%02d",
currentMint,currentSec, durationMint,durationSec));
}
// Toast.makeText(getApplicationContext(), ""+X, 10000);
T = (TextView)findViewById(R.id.textView1);
T.setText(""+X);
}
private View.OnClickListener Lang = new View.OnClickListener() {
@Override
public void onClick(View v) {
ListView listView = (ListView) findViewById(R.id.listView1);
String [] Change;
int index = listView.getFirstVisiblePosition();
View v1 = listView.getChildAt(0);
int top = (v1 == null) ? 0 : v1.getTop();
if(lang){
Change = LyricsH;
lang = false;
}
else{
Change = LyricsE;
lang = true;
}
/* ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this, R.layout.list,R.id.textView2, Change);
listView.setAdapter(adapter);
listView.setSelectionFromTop(index, top); */
dataAdapter = new arrayAdapter(MainActivity.this, Change);
listView.setAdapter(dataAdapter);
listView.setSelectionFromTop(index, top);
}
};
public boolean fontMag(){
return lang;
}
public class arrayAdapter extends ArrayAdapter<String[]> {
private final Context context;
private final String[] lyrics;
public arrayAdapter(Context context, String[]lyrics ) {
super(context, R.layout.list);
this.context = context;
this.lyrics = lyrics;
}
public int getCount() {
return lyrics.length;
}
public String[] getItem(int position) {
return (lyrics);
}
public long getItemId(int arg0) {
return arg0;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null) {
convertView = inflater.inflate(R.layout.list, parent, false);
}
TextView textView = ((TextView) convertView.findViewById(R.id.textView2));
textView.setText(lyrics[position]);
return convertView;
}
}
}
我可能会出错的任何指示？
答案 0 :(得分：1)
必须引起空指针异常，因为您的视图未正确充气..请发布logcat详细信息......
也是实现目标的更好方法
int wantedPosition = 10; // Whatever position you're looking for
int firstPosition = listView.getFirstVisiblePosition() - listView.getHeaderViewsCount(); // This is the same as child #0
int wantedChild = wantedPosition - firstPosition;
// Say, first visible position is 8, you want position 10, wantedChild will now be 2
// So that means your view is child #2 in the ViewGroup:
if (wantedChild < 0 || wantedChild >= listView.getChildCount()) {
Log.w(TAG, "Unable to get view for desired position, because it's not being displayed on screen.");
return;
}
// Could also check if wantedPosition is between listView.getFirstVisiblePosition() and listView.getLastVisiblePosition() instead.
View wantedView = listView.getChildAt(wantedChild);
请参阅此link