音頻條形圖

一個簡單的案例：可以看到音樂app上有些音頻條，隨着音調的大小條形圖也發生變化，在這裏不去真實地監聽音頻輸入了，只是用一些數字來模擬即可。

條形圖不斷變化。

public class VoiceView extends View {

    private static final String TAG = "VoiceView";

    /**
     * 小矩形的總數
     */
    private int mRectCount;
    private int mWidth;
    /**
     * 小矩形的寬度
     */
    private int mRectWidth;
    /**
     * 小矩形底部所在的高度
     */
    private int mRectHeight;
    private float mRandom;
    /**
     * 兩個小矩形之間的間距
     */
    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，這裏使用的是隨機數
             */
            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);
    }
}