android - 如何将 Canvas 保留在布局内？

Question

我的代码:

public class MainActivity extends GraphicsActivity{    

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new MyView(this));

        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(0xffffffff);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(12);

        mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },
                                       0.4f, 6, 3.5f);
        mPaint.setMaskFilter(mEmboss);

        //mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
    }

    private Paint       mPaint;
    private MaskFilter  mEmboss;

    public class MyView extends View {

        private Bitmap  mBitmap;
        private Canvas  mCanvas;
        private Path    mPath;
        private Paint   mBitmapPaint;

        public MyView(Context c) {
            super(c);

            Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.t01);
            Display  display = getWindowManager().getDefaultDisplay();
            int height = display.getWidth();
            int width = display.getHeight();
            mBitmap = Bitmap.createScaledBitmap(bmp, height, width, true);
            //mBitmap = Bitmap.createBitmap(320, 480, Bitmap.Config.ARGB_8888);
            mCanvas = new Canvas(mBitmap);
            mPath = new Path();
            mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        }

        @Override
        protected void onDraw(Canvas canvas) {

            canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);

            canvas.drawPath(mPath, mPaint);
        }

        private float mX, mY;
        private static final float TOUCH_TOLERANCE = 4;

        private void touch_start(float x, float y) {
            mPath.reset();
            mPath.moveTo(x, y);
            mX = x;
            mY = y;
        }
        private void touch_move(float x, float y) {
            float dx = Math.abs(x - mX);
            float dy = Math.abs(y - mY);
            if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
                mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
                mX = x;
                mY = y;
            }
        }
        private void touch_up() {
            mPath.lineTo(mX, mY);
            // commit the path to our offscreen
            mCanvas.drawPath(mPath, mPaint);
            // kill this so we don't double draw
            mPath.reset();
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float x = event.getX();
            float y = event.getY();

            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    touch_start(x, y);
                    invalidate();
                    break;
                case MotionEvent.ACTION_MOVE:
                    touch_move(x, y);
                    invalidate();
                    break;
                case MotionEvent.ACTION_UP:
                    touch_up();
                    invalidate();
                    break;
            }
            return true;
        }
    }

}

我的 xml:

<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" >

    <ImageView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:src="@drawable/t01"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true" />

</RelativeLayout>

现在我想将 Activity 中的 View 添加到此 xml，并且我想将此 View 放置在布局上，以便必须看到图像和 View 。实际上，我正在尝试在图像中的字母线条内绘制。就像追踪这封信一样。而且我也不希望我的 Canvas 绘图排除图像中我的字母的轮廓。如果它穿过，那么我想发出一些警告声音。 请帮我怎么做？提前致谢。

Answer 1

当我尝试 MarvinLabs 给出的答案时，我得到 Inflate Exception。所以尝试使用java本身编写代码。我的代码对我有用:

public class MainActivity extends GraphicsActivity{

    private Button clearButton;
    MyView signature;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        signature = new MyView(this);

        RelativeLayout myLayout = new RelativeLayout(this);
        myLayout.setLayoutParams(new RelativeLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));

        clearButton = new Button(this);
        clearButton.setText("Clear");
        clearButton.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // To clear the drawn lines with finger.
                Intent intent = new Intent(MainActivity.this, MainActivity.class);
            startActivity(intent);
            finish();
            }
        });

        myLayout.addView(signature);
        myLayout.addView(clearButton);

        RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(100, LayoutParams.WRAP_CONTENT);
        params.addRule(RelativeLayout.ALIGN_PARENT_TOP);
        params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
        clearButton.setLayoutParams(params);

        clearButton.bringToFront();
        this.setContentView(myLayout);

        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(0xffffffff);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(12);

        mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },
                                       0.4f, 6, 3.5f);
        mPaint.setMaskFilter(mEmboss);

    }

    private Paint       mPaint;
    private MaskFilter  mEmboss;


    public class MyView extends View {

        private static final float MINP = 0.25f;
        private static final float MAXP = 0.75f;

        private Bitmap  mBitmap;
        private Canvas  mCanvas;
        private Path    mPath;
        private Paint   mBitmapPaint;

        public MyView(Context c) {
            super(c);

            Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.t01);
            Display  display = getWindowManager().getDefaultDisplay();
            int height = display.getWidth();
            int width = display.getHeight();
            mBitmap = Bitmap.createScaledBitmap(bmp, height, width, true);
            mCanvas = new Canvas(mBitmap);
            mPath = new Path();
            mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        }


        @Override
        protected void onDraw(Canvas canvas) {

            canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);

            canvas.drawPath(mPath, mPaint);
        }

        private float mX, mY;
        private static final float TOUCH_TOLERANCE = 4;

        private void touch_start(float x, float y) {
            mPath.reset();
            mPath.moveTo(x, y);
            mX = x;
            mY = y;
        }
        private void touch_move(float x, float y) {
            float dx = Math.abs(x - mX);
            float dy = Math.abs(y - mY);
            if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
                mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
                mX = x;
                mY = y;
            }
        }
        private void touch_up() {
            mPath.lineTo(mX, mY);
            // commit the path to our offscreen
            mCanvas.drawPath(mPath, mPaint);
            // kill this so we don't double draw
            mPath.reset();
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float x = event.getX();
            float y = event.getY();

            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    touch_start(x, y);
                    invalidate();
                    break;
                case MotionEvent.ACTION_MOVE:
                    touch_move(x, y);
                    invalidate();
                    break;
                case MotionEvent.ACTION_UP:
                    touch_up();
                    invalidate();
                    break;
            }
            return true;
        }
    }
}

感谢您的支持和帮助。