Android-滑動解鎖高亮文字自定義TextView

public class HightLightTextView extends TextView {

    // 存儲view的寬度  
    private int mTextViewWidth = 0;
    // 畫筆  
    private Paint mPaint;
    // 線性渲染  
    private LinearGradient mLinearGradient;
    // 存儲變換的matrix  
    private Matrix matrix;
    // 移動距離  
    private int mTranslateX = 0;


    // 構造方法  
    public HightLightTextView(Context context) {
        this(context, null);
    }

    public HightLightTextView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public HightLightTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    /**
     * view的調用過程:構造方法->onFinishInflate->onSizeChanged->onDraw
     */
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        // 獲取view的寬度，初始化畫筆等初始屬性  
        if (mTextViewWidth == 0) {
            mTextViewWidth = getMeasuredWidth();
            // 如果寬度大於0的話，則初始化  
            if (mTextViewWidth > 0) {
                // 初始化畫筆  
                mPaint = getPaint();
                // 線性渲染  
                mLinearGradient = new LinearGradient(0, getMeasuredHeight(), mTextViewWidth, 0,
                        new int[]{0X55FFFFFF, 0XFFFFFFFF, 0X55FFFFFF},
                        new float[]{0, 0.5f, 1}, Shader.TileMode.CLAMP);
                mPaint.setShader(mLinearGradient);
                matrix = new Matrix();
            }
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if (matrix != null) {
            mTranslateX += mTextViewWidth / 10;
            // 如果移動的距離大於兩倍的寬度，則重新開始移動  
            if (mTranslateX > 2 * mTextViewWidth) {
                mTranslateX = -mTextViewWidth;
            }
            // 平移matrix  
            matrix.setTranslate(mTranslateX, 0);
            // 設置線性變化的matrix  
            mLinearGradient.setLocalMatrix(matrix);
            // 延遲50ms重繪  (重繪時會重新調用onDraw)
            postInvalidateDelayed(50);
        }
    }

}