Android图像处理（二） 画画板

思路：

建立一个bitmap副本
给imageview设置触摸监听
在两个触摸点之间画一条线canvas.drawLine(mStartx,mStarty,x,y,mPaint)
然后mImageView.setImageBitmap(mAltBitmap);
可以设置不同画笔颜色，粗细等
也可以改变画布颜色。

布局：

<LinearLayout  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"  android:orientation="vertical"  tools:context="cn.zsp.huahuaban.MainActivity"> <ImageView  android:id="@+id/iv"  android:layout_width="match_parent"  android:layout_height="320dp"  /></LinearLayout></pre>

代码：

cn.zsp.huahuaban;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Matrix;import android.graphics.Paint;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import android.view.MotionEvent;import android.view.View;import android.widget.ImageView;public class MainActivity extends AppCompatActivity {    private static final String TAG = "zsp"; private ImageView mImageView; private Paint mPaint; private Bitmap mAltBitmap; private int mStarty; private int mStartx;  @Override  protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);  setContentView(R.layout.activity_main);  mImageView = (ImageView) findViewById(R.id.iv);  //得到原图  Bitmap bitmap= BitmapFactory.decodeResource(getResources(),R.drawable.sc);  mImageView.setImageBitmap(bitmap);  //获取副本  mAltBitmap = Bitmap.createBitmap(bitmap.getWidth(),bitmap.getHeight(),bitmap.getConfig());  mPaint = new Paint();  mPaint.setColor(Color.BLACK);  mPaint.setStyle(Paint.Style.FILL);  //    mPaint.setStrokeWidth(20);  final Canvas canvas=new Canvas(mAltBitmap);  canvas.drawBitmap(bitmap,new Matrix(),mPaint);  canvas.drawText("niafdsaf",0,0,mPaint);  mImageView.setOnTouchListener(new View.OnTouchListener() {            @Override  public boolean onTouch(View v, MotionEvent event) {                switch (event.getAction()){                    case MotionEvent.ACTION_DOWN:                        Log.e(TAG, "onTouch: 按下了" );  mStartx = (int) event.getX();  mStarty = (int) event.getY(); break; case MotionEvent.ACTION_MOVE:                        Log.e(TAG, "onTouch: 移动了" ); int x= (int) event.getX(); int y= (int) event.getY();  canvas.drawLine(mStartx,mStarty,x,y,mPaint);//两点间划线  mImageView.setImageBitmap(mAltBitmap);  mStartx=x;  mStarty=y;//重置  break; case MotionEvent.ACTION_UP:                        Log.e(TAG, "onTouch: 离开了" ); break;  }                return true;  }        });  }}</pre>