音频条形图

一个简单的案例：可以看到音乐app上有些音频条，随着音调的大小条形图也发生变化，在这里不去真实地监听音频输入了，只是用一些数字来模拟即可。

条形图不断变化。

public class VoiceView extends View {

    private static final String TAG = "VoiceView";

    /**
     * 小矩形的总数
     */
    private int mRectCount;
    private int mWidth;
    /**
     * 小矩形的宽度
     */
    private int mRectWidth;
    /**
     * 小矩形底部所在的高度
     */
    private int mRectHeight;
    private float mRandom;
    /**
     * 两个小矩形之间的间距
     */
    private int offset;
    private Paint mPaint;
    /**
     * 小矩形的着色器
     */
    private LinearGradient mLinearGradient;

    public VoiceView(Context context) {
        this(context, null);
    }

    public VoiceView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public VoiceView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initData();
    }

    private void initData() {
        mRectCount = 10;
        offset = 5;
        mPaint = new Paint();
        mPaint.setColor(Color.GRAY);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        mWidth = getWidth();
        mRectHeight = getHeight()/2;
        mRectWidth = (int) (mWidth*0.6/mRectCount);
        mLinearGradient = new LinearGradient(0, 0, mRectWidth, mRectHeight, Color.YELLOW, Color.BLUE, Shader.TileMode.CLAMP);
        mPaint.setShader(mLinearGradient);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        /**
         * 小矩形的高
         */

        for (int i=0; i<mRectCount; i++){
            mRandom = (float) Math.random();
            /**
             * 矩形的高度，这里使用的是随机数
             */
            float currentHeight = mRectHeight*mRandom;
            canvas.drawRect((float) (mWidth*0.4/2+mRectWidth*i+offset),
                    currentHeight,
                    (float) (mWidth*0.4/2+mRectWidth*(i+1)),
                    mRectHeight,
                    mPaint
            );
        }
        postInvalidateDelayed(300);
    }
}