Question

我在我的项目中制作了一个导航抽屉，然后我想制作一个左右滑动的按钮，但我的应用停止并阻止。

我收到此错误：

java.lang.RuntimeException: Unable to start activity ComponentInfo{radiofm.arabelradio/radiofm.arabelradio.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference

程序：

package radiofm.arabelradio;

import android.content.res.Configuration;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.os.AsyncTask;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;

import java.io.IOException;

import static android.media.AudioManager.STREAM_MUSIC;

public class MainActivity extends AppCompatActivity {


    ImageButton id_play;
    MediaPlayer mediaPlayer;
    boolean prepared = false;
    boolean started =false;
    String stream ="http://arabelfm.ice.infomaniak.ch/arabelprodcastfm.mp3";
    //main_page contain arabel_photo player for radio



    private DrawerLayout mDrawerLayout;
    private ActionBarDrawerToggle mToggle;





    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        /////////////////////////////////////////////////////////////////////////////
        id_play = (ImageButton) findViewById(R.id.id_play);
        id_play.setEnabled(false);
        //id_play.setText("LOADING");
        mediaPlayer = new MediaPlayer();
        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
        new PlayerTask().execute(stream);
        id_play.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (started){
                    started=false;
                    mediaPlayer.pause();
                    id_play.setImageResource(R.drawable.play);
                   // id_play.setText("PLAY");
                }
                else {
                    started=true;
                    mediaPlayer.start();
                    id_play.setImageResource(R.drawable.pause);

                    //id_play.setText("PAUSE");
                }
            }
        });
        //main_page contain arabel_photo player for radio//////////////////////////:




        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
        mToggle=new ActionBarDrawerToggle(this,mDrawerLayout, R.string.open,R.string.close);
        mDrawerLayout.addDrawerListener(mToggle);
        mToggle.syncState();
        getActionBar().setDisplayHomeAsUpEnabled(true);
        getActionBar().setHomeButtonEnabled(true);



    }




//////////////////////////////////////////////////////////////////////////////////////////////////////////
    class PlayerTask extends AsyncTask<String,Void,Boolean>{

        @Override
        protected Boolean doInBackground(String... strings) {

            try {
                mediaPlayer.setDataSource(strings[0] );
                mediaPlayer.prepare();
                prepared=true;
            } catch (IOException e) {
                e.printStackTrace();
            }

            return prepared;
        }

        @Override
        protected void onPostExecute(Boolean aBoolean) {
            super.onPostExecute(aBoolean);
            id_play.setEnabled(true);
            id_play.setImageResource(R.drawable.play);

            // id_play.setText("PLAY");
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        if(started){
            mediaPlayer.pause();
        }
    }


    @Override
    protected void onResume() {
        super.onResume();
        if(started){
            mediaPlayer.start();
        }
    }


    @Override
    protected void onDestroy() {
        super.onDestroy();
        if(prepared){
            mediaPlayer.release();
        }
    }
/////////////////////////////////////////////////////////////////////////////////////////////////////
    //main_page contain arabel_photo player for radio//////////////////////////:



    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        if (mToggle.onOptionsItemSelected(item))
        {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

Answer 1

您的活动主题可能没有操作栏，而函数getActionBar（）返回null实例。

Answer 2

只需在代码中添加

即可

getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);

我的应用程序错误和停止我不知道为什么

2 个答案: