我已经尝试并完成了我在互联网和 stackoverflow 上阅读的所有内容来解决我的问题，但到目前为止还没有成功。我想做的基本上是单击按钮并在 MediaPlayer 缓冲来自互联网的流时显示 ProgressDialog。我遇到了许多类型的上下文错误(NullPointerException)和线程问题。以下是有关代码的一些详细信息:
- 该按钮是一个切换按钮，其背景图像基于事件(打开、关闭、未连接时显示不同的图像按钮)；
- 函数
prepareStream()应该在线程中运行，并在加载流后关闭 ProgressDialog。它正在调用 BBC 广播电台的 http 流； - 我猜问题出在上下文上...我在代码上放置了一些 Log.d 标签来检查问题发生的位置，O 发现问题出在
mediaPlayer.start()方法。
他走了小男孩:
package com.android.iFocus;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.media.MediaPlayer;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.CompoundButton;
import android.widget.ToggleButton;
import com.insightoverflow.iFocus.R;
public class iFocusActivity extends Activity implements OnClickListener {
//Declare Controls
public int count = 0;
public int x = 1;
public MediaPlayer mediaPlayer = null;
ToggleButton toggleRain = null;
Button buttonAbout = null;
Button buttonMethod = null;
Button buttonLink = null;
public ProgressDialog progressDialog;
public static final String TAG = "getFocused";
public boolean isOnline() {
//Check if internet is connected
ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
return activeNetworkInfo != null;
}
public void prepareStream(final Context context){
if(isOnline()){
// init player
new Thread()
{
public void run()
{
try {
sleep(1500);
//progressDialog.show();
mediaPlayer = MediaPlayer.create(context, Uri.parse("http://vprbbc.streamguys.net:80/vprbbc24.mp3"), null);
x=2;
} catch (Exception e){
x=3;
}
//dismiss the progressdialog
progressDialog.dismiss();
}
}.start();
} else {
x=3;
}
}
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
// load layout
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// load controls
toggleRain = (ToggleButton)findViewById(R.id.toggleRain);
buttonAbout = (Button)findViewById(R.id.buttonAbout);
buttonMethod = (Button)findViewById(R.id.buttonMethod);
buttonLink = (Button)findViewById(R.id.buttonLink);
//Define Listeners (click event handler)
toggleRain.setOnClickListener(this);
buttonAbout.setOnClickListener(this);
buttonMethod.setOnClickListener(this);
buttonLink.setOnClickListener(this);
// init state for player
count = 0;
//Context APP
//Context appContext = this.getApplicationContext();
if (!isOnline()){
toggleRain.setBackgroundDrawable(getResources().getDrawable(R.drawable.notconnectedbutton));
x=3;
}
}
public void onClick(View v) {
if( toggleRain.getId() == ((Button)v).getId() ){
//meanwhile device is offline, do this
do {
toggleRain.setBackgroundDrawable(getResources().getDrawable(R.drawable.notconnectedbutton));
try{
Thread.currentThread();
//do what you want to do before sleeping
Thread.sleep(1000);//sleep for 1000 ms
//do what you want to do after sleeptig
} catch(Exception ie){}
continue;
}while (!isOnline());
//If device is online, go for this
if (((CompoundButton) toggleRain).isChecked()) {
toggleRain.setBackgroundDrawable(getResources().getDrawable(R.drawable.stopbutton));
} else {
toggleRain.setBackgroundDrawable(getResources().getDrawable(R.drawable.playbutton));
}
//----> HERE GOES WHERE I THINK IS THE PROBLEM <-----
//---------------------------------------------------
if (isOnline()){
//If music is not playing, start music
if(count==0){
Log.d(TAG, "START PROGRESS DIALOG");
progressDialog = ProgressDialog.show(v.getContext(), "Load", "Loading");
//progressDialog = ProgressDialog.show(, "Load", "Loading...", true, false);
Log.d(TAG, "END PROGRESS DIALOG");
Log.d(TAG, "START PREPARE STREAM");
Context context = v.getContext();
prepareStream(context);
Log.d(TAG, "END PREPARE STREAM");
Log.d(TAG, "START MEDIA PLAYER START");
//LOG CAT START AND END ALL OF THE OTHER LOG TAGS, EXCEPT THIS mediaplayer.start()
mediaPlayer.start();
Log.d(TAG, "END MEDIAPLAYER START");
count = 1;
} else {
mediaPlayer.pause();
count = 0;
}
}
} else if( buttonAbout.getId() == ((Button)v).getId() ){
Intent i = new Intent(iFocusActivity.this, AboutActivity.class);
startActivity(i);
}
else if ( buttonMethod.getId() == ((Button)v).getId() ){
Intent o = new Intent(iFocusActivity.this, MethodActivity.class);
startActivity(o);
}
else if ( buttonLink.getId() == ((Button)v).getId() ){
Uri uri = Uri.parse( "http://getFocused.in" );
startActivity( new Intent( Intent.ACTION_VIEW, uri ) );
}
}
@Override
protected void onDestroy() {
super.onDestroy();
if(mediaPlayer != null) {
mediaPlayer.stop();
mediaPlayer.release();
mediaPlayer = null;
}
}
}
所以 logcat 告诉我 mediaPlayer.start() 被调用的时间 NullPointerException
最佳答案
您必须在 runOnUiThread() 方法中运行 ProgressDialog.show()(不在主 UI 线程中)。请参阅 Android 文档 here
创建一个进度对话框对象，然后编写此代码。
runOnUiThread(new Runnable(){
@Override
public void run() {
dialog.show();
}
});
此外，调用 prepareStream() 和 mediaplayer.start() 应该进入单独的线程，而不是主 UI 线程。
解决掉与线程相关的问题就可以了。
关于java - 线程、MediaPlayer、ProgressDialog 和上下文问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/7835411/