Canvas基础

import android.app.Activity;import android.content.Context;import android.graphics.Bitmap;import android.graphics.Bitmap.Config;import android.graphics.BitmapFactory;import android.graphics.Canvas;import android.graphics.Paint;import android.os.Bundle;import android.view.Menu;import android.view.MotionEvent;import android.view.View;import android.view.animation.AlphaAnimation;import android.view.animation.Animation;public class MainActivity extends Activity {    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(new MyView(this));    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        getMenuInflater().inflate(R.menu.activity_main, menu);        return true;    }    class MyView extends View {        Canvas mCanvas;        Bitmap mBitmap;        Paint mPaint;        float movex, movey;        float X_r, Y_r;        public MyView(Context context) {            super(context);            init();        }        public void init() {            mBitmap = Bitmap.createBitmap(240, 300, Config.ARGB_8888);            mCanvas = new Canvas(mBitmap);            mBitmap = BitmapFactory.decodeResource(getResources(),                    R.drawable.studycenter_userinfo_back);            X_r = -mBitmap.getWidth();            Y_r = -mBitmap.getHeight();            mPaint = new Paint();            mPaint.setColor(0xFFFFFFFF);        }        protected void onDraw(Canvas canvas) {            canvas.drawBitmap(mBitmap, X_r, Y_r, mPaint);            System.out.println("onDraw");            super.onDraw(canvas);        }        @Override        public boolean onTouchEvent(MotionEvent event) {            float x = event.getX();            float y = event.getY();            switch (event.getAction()) {            // 点击时的(x,y)，记录初始位置            case MotionEvent.ACTION_DOWN:                Animation alphaAnimation = new AlphaAnimation(0.1f, 1.0f);                 alphaAnimation.setDuration(500);                this.startAnimation(alphaAnimation);                movex = mBitmap.getWidth() / 2;                movey = mBitmap.getHeight() / 2;                X_r = x - movex;                Y_r = y - movey;                mPaint.setAlpha(255);                invalidate();                break;            // 移动时更新(x,y)，同时更新图片            case MotionEvent.ACTION_MOVE:                movex = mBitmap.getWidth() / 2;                movey = mBitmap.getHeight() / 2;                X_r = x - movex;                Y_r = y - movey;                invalidate();                break;            // 弹起时更新(x,y)，并记录位置            case MotionEvent.ACTION_UP:                mPaint.setAlpha(0);                invalidate();                break;            }            return true;        }    }}