一起来学习Android自定义控件2-简单的写字板控件

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <declare-styleable name="WritingBoardView">
        <attr name="boardBackground" format="color"></attr> <!--画板颜色-->
        <attr name="paintColor" format="color"></attr> <!--画笔颜色-->
        <attr name="paintWidth" format="dimension"></attr> <!--画笔宽度-->
    </declare-styleable>
</resources>

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:custom="http://schemas.android.com/apk/res-auto"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.qiangyu.test.writingboardview.MainActivity">

    <com.qiangyu.test.writingboardview.view.WritingBoardView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        custom:paintColor="@color/colorAccent"
        custom:boardBackground="@color/colorPrimary"
        custom:paintWidth="3dp"/>
</RelativeLayout>

   private int mBoardBackground;//画板颜色
    private int mPaintColor;//画笔颜色
    private int mPaintWidth;//画笔宽度
    private Path mPath;
    private Paint mPaint;//画笔

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

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

    public WritingBoardView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context,attrs);
    }



 private void init(Context context,AttributeSet attrs) {
        TypedArray a = context.obtainStyledAttributes(attrs,R.styleable.WritingBoardView);
        mBoardBackground =   a.getColor(R.styleable.WritingBoardView_boardBackground,Color.WHITE);
        mPaintColor =   a.getColor(R.styleable.WritingBoardView_paintColor,Color.BLUE);
        mPaintWidth = a.getDimensionPixelSize(R.styleable.WritingBoardView_paintWidth,
                (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,5,getResources().getDisplayMetrics()));
        a.recycle();
        mPaint = new Paint();
        mPath = new Path();
        setBackgroundColor(mBoardBackground);
        mPaint.setColor(mPaintColor);
        mPaint.setStrokeWidth(mPaintWidth);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setAntiAlias(true);
    }

/**
 * The Path class encapsulates compound (multiple contour) geometric paths
 * consisting of straight line segments, quadratic curves, and cubic curves.
 * It can be drawn with canvas.drawPath(path, paint), either filled or stroked
 * (based on the paint‘s Style), or it can be used for clipping or to draw
 * text on a path.
 */
public class Path {

    ...

}

  /**
     * Set the beginning of the next contour to the point (x,y).
     *
     * @param x The x-coordinate of the start of a new contour
     * @param y The y-coordinate of the start of a new contour
     */
    public void moveTo(float x, float y) {
        native_moveTo(mNativePath, x, y);
    }

/**
     * Add a line from the last point to the specified point (x,y).
     * If no moveTo() call has been made for this contour, the first point is
     * automatically set to (0,0).
     *
     * @param x The x-coordinate of the end of a line
     * @param y The y-coordinate of the end of a line
     */
    public void lineTo(float x, float y) {
        isSimplePath = false;
        native_lineTo(mNativePath, x, y);
    }

 @Override
    public boolean onTouchEvent(MotionEvent event) {
        float touchX = event.getX();
        float touchY = event.getY();
        switch (event.getAction()){
            case MotionEvent.ACTION_DOWN:
                mPath.moveTo(touchX,touchY);//重新设置即将出现的线的起点
                break;
            case MotionEvent.ACTION_MOVE:
                mPath.lineTo(touchX,touchY);//连线
                break;
            case MotionEvent.ACTION_UP:
                break;
        }
        invalidate();//通知系统重绘
        return true;//要处理当前事件
    }

 @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawPath(mPath,mPaint);
    }