单击按钮在 android studio 中不起作用

Question

对于我正在创建的应用程序，它不允许我指定如何处理按钮，而是给我错误。该应用程序有助于在三首音乐歌曲之间切换。

代码已关闭

    package com.example.atvan.babysleeper;

import android.media.MediaPlayer;
import android.os.Handler;
import android.os.Message;
import android.provider.MediaStore;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.SeekBar;
import android.widget.TextView;

import com.example.atvan.babysleep.R;

public class MainActivity extends AppCompatActivity {

    Button playBtn;
    Button one;
    Button two;
    Button three;
    SeekBar positionBar;
    SeekBar volumeBar;
    TextView elapsedTimeLabel;
    TextView remainingTimelabel;
    MediaPlayer mp;
    int totalTime;

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

        playBtn = (Button) findViewById(R.id.playBtn);
        elapsedTimeLabel = (TextView) findViewById(R.id.elapsedTimeLabel);
        remainingTimelabel = (TextView) findViewById(R.id.remainingTimeLabel);
        one = (Button) findViewById(R.id.one);
        two = (Button) findViewById(R.id.two);
        three = (Button) findViewById(R.id.three);


        //Media player

        public void setOne(View view){
            mp = MediaPlayer.create(this, R.raw.music3);
        }
        public void setTwo(View view){
            mp = MediaPlayer.create(this, R.raw.music2);
        }
        public void setThree(View view){
            mp = MediaPlayer.create(this, R.raw.music1);

        }


        mp.setLooping(true);
        mp.seekTo(0);
        mp.setVolume(0.5f,0.5f);
        totalTime = mp.getDuration();

        //position Bar
        positionBar = (SeekBar) findViewById(R.id.positionBar);
        positionBar.setMax(totalTime);
        positionBar.setOnSeekBarChangeListener(
                new SeekBar.OnSeekBarChangeListener() {
                    @Override
                    public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                        if (fromUser) {
                            mp.seekTo(progress);
                            positionBar.setProgress(progress);
                        }
                    }

                    @Override
                    public void onStartTrackingTouch(SeekBar seekBar) {

                    }

                    @Override
                    public void onStopTrackingTouch(SeekBar seekBar) {

                    }
                }
        );

        //Volume Bar
        volumeBar = (SeekBar) findViewById(R.id.volumeBar);
        volumeBar.setOnSeekBarChangeListener(
                new SeekBar.OnSeekBarChangeListener() {
                    @Override
                    public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                        float volumeNum = progress/100f;
                        mp.setVolume(volumeNum, volumeNum);
                    }

                    @Override
                    public void onStartTrackingTouch(SeekBar seekBar) {

                    }

                    @Override
                    public void onStopTrackingTouch(SeekBar seekBar) {

                    }
                }
        );

        //thread (update positionBar amd timeLabel)
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (mp != null) {
                    try{
                        Message msg = new Message();
                        msg.what = mp.getCurrentPosition();
                        handler.sendMessage(msg);
                        Thread.sleep(1000);
                    }catch (InterruptedException e){}
                }
            }
        }).start();



    }

    private Handler handler;

    {
        handler = new Handler(new Handler.Callback() {
            @Override
            public boolean handleMessage(Message msg) {
                int currentPosition = msg.what;
                // Update positionBar.
                positionBar.setProgress(currentPosition);

                // Update Labels.
                String elapsedTime = createTimeLabel(currentPosition);
                elapsedTimeLabel.setText(elapsedTime);

                String remainingTime = "- " + createTimeLabel(totalTime - currentPosition);
                remainingTimelabel.setText(remainingTime);

                return true;
            }
        });
    }

    public String createTimeLabel(int time) {
        String timeLabel = "";
        int min = time / 1000 / 60;
        int sec = time /1000 % 60;

        timeLabel = min + ":";
        if (sec<10) timeLabel += "0";
        timeLabel += sec;

        return timeLabel;
    }

    public void playBtnClick(View view) {
        if (!mp.isPlaying()){
            //stopping
            mp.start();
            playBtn.setBackgroundResource(R.drawable.stop);
        } else {
            //playing
            mp.pause();
            playBtn.setBackgroundResource(R.drawable.play);

        }
    }

它给出的错误是我的媒体播放器部分有一个非法的表达式开头。它还表示给予；那里的某个地方。当放在代码末尾时。它不会给出任何错误，但应用程序不会运行

错误在这里

Answer 1

你不能只在函数中间定义函数。它们需要在 class 范围内，在 onCreate 之外。

Answer 2

您已经在 onCreate() 中定义了所有 3 个方法。将它们放在 onCreate 之外并从任何你想要的地方调用它们。如果默认情况下您需要 setOne() 则只需在 onCreate() 中调用 setOne()。

//媒体播放器

    public void setOne(View view){
        mp = MediaPlayer.create(this, R.raw.music3);
    }
    public void setTwo(View view){
        mp = MediaPlayer.create(this, R.raw.music2);
    }
    public void setThree(View view){
        mp = MediaPlayer.create(this, R.raw.music1);

    }

类似于

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

    playBtn = (Button) findViewById(R.id.playBtn);
    elapsedTimeLabel = (TextView) findViewById(R.id.elapsedTimeLabel);
    remainingTimelabel = (TextView) findViewById(R.id.remainingTimeLabel);
    one = (Button) findViewById(R.id.one);
    two = (Button) findViewById(R.id.two);
    three = (Button) findViewById(R.id.three);

    //call setOne or setTwo or setThree based on what you want here.

Answer 3

这里几乎没有逻辑错误。首先，您不能在另一个方法中编写方法，因此请从 onCreate() 中删除以下代码行并将其写在外部：

public void setOne(View view){ mp = MediaPlayer.create(this, R.raw.music3); } 
public void setTwo(View view){ mp = MediaPlayer.create(this, R.raw.music2); } 
public void setThree(View view){ mp = MediaPlayer.create(this, R.raw.music1); }

第二件事是你在这些方法中初始化你的 mediaPlayer，所以你应该做的是最初调用来自onCreate()的setOne()方法，当前播放歌曲结束后调用其他方法。

请完成 this 教程，虽然它显示 "Building a media player in a service" 但你可以在你的 activity 中完成它，并为你完成“ 第三步 –构建 MediaPlayer" 很重要。

单击按钮在 android studio 中不起作用

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