Android自定义View实现柱状波形图的绘制

来源：jb51　　时间：2022/8/16 9:55:00　　对本文有异议

前言

柱状波形图是一种常见的图形。一个个柱子按顺序排列，构成一个波形图。

柱子的高度由输入数据决定。如果输入的是音频的音量，则可得到一个声波图。

在一些音频软件中，我们也可以左右拖动声波，来改变音频的播放进度

本文举例的自定View，实现如下功能：

以柱状形式展示数据的大小
标明图形当前最中间的数据
可以横向拖动进度，进度就是让某个特定的数据居中展示
可以改变左右两边的柱子颜色
可以调整柱子的宽度
拖动完毕后监听当前进度

实现

首先创建类SoundWaveView继承自View

我们可以先记录给定的宽高，方便后面找到View的中间点

private int viewWid = 1000;     // px
private int viewHeight = 100;   // px
 
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    viewWid = w;
    viewHeight = h;
    // ..
}

基本属性

例如柱子的颜色，宽度。可以设置个属性来记录，并开放出去可由外部来设置。

private float barWidDp = 1.5f;
private float barWidPx = 3f;
private float barGapPx = barWidPx / 2;
private int barCount = 1;       // 当前宽度能绘制多少个柱子
 
private final Paint paint = new Paint();
private int leftColor = Color.GREEN;
private int rightColor = Color.LTGRAY;
private int middleLineColor = Color.parseColor("#55000000");

设计监听器

拖动完毕后，可以将当前进度通知出去。也可以直接把触摸事件传出去。

public interface OnEvent {
    void onMoveEnd(); // 停止拖动了
 
    void onDragTouchEvent(MotionEvent event);
}
 
private OnEvent onEventListener;
 
private void tellOnMoveEnd() {
    if (onEventListener != null) {
        onEventListener.onMoveEnd();
    }
}

绘制图形

在onDraw方法中根据数据绘制图形

本例没有设计背景，直接绘制数据。

图形需求之一是要求某个数据能居中显示，我们用midIndex来标记这个数据的下标。

比较简单粗暴的实现方法，遍历整个数据列表，计算出每个数据的x坐标。超出范围的不绘制，范围内的逐一绘制。

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    if (dataList == null || dataList.isEmpty()) {
        // draw nothing
        drawMiddleLine(canvas);
        return;
    }
    float x0 = viewWid / 2.0f;
 
    if (midIndex > 0) {
        x0 = x0 - (barGapPx + barWidPx) * midIndex; // 可能是负数
    }
    for (int i = 0; i < dataList.size(); i++) {
        float d = dataList.get(i);
        float x = x0 + (barWidPx + barGapPx) * i;
        if (x < 0) {
            continue;
        }
        if (x > viewWid) {
            break;
        }
        if (i <= midIndex) {
            paint.setColor(leftColor);
        } else {
            paint.setColor(rightColor);
        }
        paint.setStrokeWidth(barWidPx);
        float bh = (d / showMaxData) * viewHeight;
        bh = Math.max(bh, 4); // 最小也要一点高度 (1)
        float bhGap = (viewHeight - bh) / 2f;
        canvas.drawLine(x, bhGap, x, viewHeight - bhGap, paint);
    }
 
    drawMiddleLine(canvas);
}
 
private void drawMiddleLine(Canvas canvas) {
    paint.setColor(middleLineColor);
    canvas.drawLine(viewWid / 2f, 0, viewWid / 2f, viewHeight, paint);
}

如果数据太小，为了更美观，也要显示一点东西

左右拖动

本例给出的思路是在SoundWaveView中直接获取触摸事件并进行处理。

简单区分一下模式，分为纯展示和可拖动模式

/**
* 单纯播放 展示 无交互
*/
public static final int MODE_PLAY = 1;
 
/**
* 允许左右拖动
*/
public static final int MODE_CAN_DRAG = 2;

复写onTouchEvent方法，如果是MODE_CAN_DRAG模式，则拦截触摸事件。判断拖动的横向（x）距离。

@Override
public boolean onTouchEvent(MotionEvent event) {
    if (mode == MODE_CAN_DRAG) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_MOVE:
                float dx = (downX - event.getX()); // 不要那么灵敏
                float movePercent = dx / viewWid;
                int dIndex = (int) (movePercent * barCount);
                int targetMidIndex = downOldMidIndex + dIndex;
                targetMidIndex = Math.max(0, targetMidIndex);
                targetMidIndex = Math.min(targetMidIndex, dataList.size() - 1);
                setMidIndex(targetMidIndex);
                Log.d(TAG, "onTouchEvent-MOVE; dx: " + dx + ", dIndex: " + dIndex + "; targetMidIndex: " + targetMidIndex);
                break;
            case MotionEvent.ACTION_DOWN:
                downX = event.getX();
                downOldMidIndex = midIndex;
                break;
            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                downOldMidIndex = midIndex;
                tellOnMoveEnd();
                break;
        }
        if (onEventListener != null) {
            onEventListener.onDragTouchEvent(event);
        }
        return true;
    }
    return super.onTouchEvent(event);
}

完整代码

文件SoundWaveView.java，这个view主要目的是展现声波，取名为「SoundWave」

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
 
import androidx.annotation.Nullable;
 
import java.util.ArrayList;
import java.util.List;
 
/**
 * @author an.rustfisher.com
 */
public class SoundWaveView extends View {
    private static final String TAG = "rustAppSoundWaveView";
 
    /**
     * 单纯播放 展示 无交互
     */
    public static final int MODE_PLAY = 1;
 
    /**
     * 允许左右拖动
     */
    public static final int MODE_CAN_DRAG = 2;
 
    private int mode = MODE_PLAY; // 1 播放
    private List<Float> dataList = new ArrayList<>(100);
    private float showMaxData = 40f; // 能显示的最大数据
    private int midIndex = 0;   // 在中间显示的数据的下标
    private float barWidDp = 1.5f;
    private float barWidPx = 3f;
    private float barGapPx = barWidPx / 2;
    private int barCount = 1;       // 当前宽度能绘制多少个柱子
    private int viewWid = 1000;     // px
    private int viewHeight = 100;   // px
 
    private final Paint paint = new Paint();
    private int leftColor = Color.GREEN;
    private int rightColor = Color.LTGRAY;
    private int middleLineColor = Color.parseColor("#55000000");
 
    private float downX = 0; // getX
    private int downOldMidIndex = 0;
 
    public interface OnEvent {
        void onMoveEnd(); // 停止拖动了
 
        void onDragTouchEvent(MotionEvent event);
    }
 
    private OnEvent onEventListener;
 
    public SoundWaveView(Context context) {
        this(context, null);
    }
 
    public SoundWaveView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }
 
    public SoundWaveView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        paint.setColor(Color.BLUE);
    }
 
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        viewWid = w;
        viewHeight = h;
        calBarPara();
        Log.d(TAG, "onSizeChanged: " + w + ", " + h);
        Log.d(TAG, "onSizeChanged: barWidPx: " + barWidPx);
    }
 
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if (dataList == null || dataList.isEmpty()) {
            // draw nothing
            drawMiddleLine(canvas);
            return;
        }
        float x0 = viewWid / 2.0f;
 
        // 绘制数据
        if (midIndex > 0) {
            x0 = x0 - (barGapPx + barWidPx) * midIndex; // 可能是负数
        }
        for (int i = 0; i < dataList.size(); i++) {
            float d = dataList.get(i);
            float x = x0 + (barWidPx + barGapPx) * i;
            if (x < 0) {
                continue;
            }
            if (x > viewWid) {
                break;
            }
            if (i <= midIndex) {
                paint.setColor(leftColor);
            } else {
                paint.setColor(rightColor);
            }
            paint.setStrokeWidth(barWidPx);
            float bh = (d / showMaxData) * viewHeight;
            bh = Math.max(bh, 4); // 最小也要一点高度
            float bhGap = (viewHeight - bh) / 2f;
            canvas.drawLine(x, bhGap, x, viewHeight - bhGap, paint);
        }
        drawMiddleLine(canvas);
    }
 
    private void drawMiddleLine(Canvas canvas) {
        paint.setColor(middleLineColor);
        canvas.drawLine(viewWid / 2f, 0, viewWid / 2f, viewHeight, paint);
    }
 
    public float getMidByPercent() {
        return midIndex / (float) (dataList.size() - 1);
    }
 
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (mode == MODE_CAN_DRAG) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_MOVE:
                    float dx = (downX - event.getX()); // 不要那么灵敏
                    float movePercent = dx / viewWid;
                    int dIndex = (int) (movePercent * barCount);
                    int targetMidIndex = downOldMidIndex + dIndex;
                    targetMidIndex = Math.max(0, targetMidIndex);
                    targetMidIndex = Math.min(targetMidIndex, dataList.size() - 1);
                    setMidIndex(targetMidIndex);
                    Log.d(TAG, "onTouchEvent-MOVE; dx: " + dx + ", dIndex: " + dIndex + "; targetMidIndex: " + targetMidIndex);
                    break;
                case MotionEvent.ACTION_DOWN:
                    downX = event.getX();
                    downOldMidIndex = midIndex;
                    break;
                case MotionEvent.ACTION_CANCEL:
                case MotionEvent.ACTION_UP:
                    downOldMidIndex = midIndex;
                    tellOnMoveEnd();
                    break;
            }
            if (onEventListener != null) {
                onEventListener.onDragTouchEvent(event);
            }
            return true;
        }
        return super.onTouchEvent(event);
    }
 
    public void setMode(int mode) {
        this.mode = mode;
    }
 
    public int getMode() {
        return mode;
    }
 
    public int getMidIndex() {
        return midIndex;
    }
 
    public List<Float> getDataList() {
        return dataList;
    }
 
    public void setOnEventListener(OnEvent onEventListener) {
        this.onEventListener = onEventListener;
    }
 
    public void clear() {
        dataList = new ArrayList<>();
        midIndex = 0;
        invalidate();
    }
 
    private void calBarPara() {
        barWidPx = dp2Px(barWidDp);
        barGapPx = barWidPx;
        barCount = (int) ((viewWid - barGapPx) / (barWidPx + barGapPx));
        paint.setStrokeWidth(barWidPx);
        Log.d(TAG, "calBarPara: barCount: " + barCount);
    }
 
    public void setDataList(List<Float> input) {
        dataList = new ArrayList<>(input);
        midIndex = 0;
        invalidate();
    }
 
    public void setMidIndex(int midIndex) {
        this.midIndex = midIndex;
        invalidate();
    }
 
    public void setMidEnd() {
        setMidIndex(dataList.size() - 1);
    }
 
    // 设置当前播放进度
    public void setPlayPercent(float percent) {
        midIndex = (int) (percent * (dataList.size() - 1));
        if (percent >= 1) {
            midIndex = dataList.size() - 1;
        }
        invalidate();
    }
 
    public void setShowMaxData(float showMaxData) {
        this.showMaxData = showMaxData;
    }
 
    public float getShowMaxData() {
        return showMaxData;
    }
 
    // 不停地插入数据
    public void addDataEnd(float f) {
        dataList.add(f);
        midIndex = dataList.size() - 1;
        invalidate();
    }
 
    public void setLeftColor(int leftColor) {
        this.leftColor = leftColor;
    }
 
    public void setRightColor(int rightColor) {
        this.rightColor = rightColor;
    }
 
    private float dp2Px(float dp) {
        float density = getContext().getResources().getDisplayMetrics().density;
        int mark = dp > 0 ? 1 : -1;
        return dp * density * mark;
    }
 
    private void tellOnMoveEnd() {
        if (onEventListener != null) {
            onEventListener.onMoveEnd();
        }
    }
}

layout中使用

<com.rustfisher.tutorial2020.customview.soundwave.SoundWaveView
    android:id="@+id/sound_wave_view"
    android:layout_width="match_parent"
    android:layout_height="100dp"
    android:layout_marginTop="4dp"
    android:background="@android:color/white"
    app:layout_constraintTop_toTopOf="parent" />

activity中使用模拟数据

private void setData1() {
    List<Float> dataList = new ArrayList<>();
    for (int i = 0; i < 1000; i++) {
        dataList.add((float) (Math.random() * soundWaveView.getShowMaxData()));
    }
    soundWaveView.setDataList(dataList);
    soundWaveView.setMidIndex(0);
 
    soundWaveView.setOnEventListener(new SoundWaveView.OnEvent() {
        @Override
        public void onMoveEnd() {
            Log.d(TAG, "onMoveEnd: " + soundWaveView.getMidIndex());
        }
 
        @Override
        public void onDragTouchEvent(MotionEvent event) {
            // 在这里可以收到触摸事件
        }
    });
}