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;

        }

    }

}