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[编程交流] Android画板

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电梯直达

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发表于 2013-6-13 10:27:04 |只看该作者 |倒序浏览

本帖最后由 sky_yx 于 2015-12-30 14:07 编辑

思路：
      自定义CustomView，重写onTouch()，和onDraw()。在onTouch中识别触屏事件，并记录触屏发生的位置。为了在ACTION_DOWN发生后能够接收到后续的触屏事件，我们需要让onTouch()返回true。
Java代码
package com.ipjmc.hello;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
public class CustomView extends View {
private int mLastX, mLastY; //上次触屏的位置
private int mCurrX, mCurrY; //当前触屏的位置
private Bitmap mBitmap;  //保存每次绘画的结果
private Paint mPaint;
public CustomView(Context context, AttributeSet attrs) {
      super(context, attrs);
      mPaint = new Paint();
}
@Override
protected void onDraw(Canvas canvas) {
      super.onDraw(canvas);
      int width = getWidth();
      int height = getHeight();
      if (mBitmap == null) {
         mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
      }
//先将结果画到Bitmap上
      Canvas tmpCanvas = new Canvas(mBitmap);
      tmpCanvas.drawLine(mLastX, mLastY, mCurrX, mCurrY, mPaint);
//再把Bitmap画到canvas上
      canvas.drawBitmap(mBitmap, 0, 0, mPaint);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
      mLastX = mCurrX;
      mLastY = mCurrY;
      mCurrX = (int) event.getX();
      mCurrY = (int) event.getY();
      switch (event.getAction()) {
      case MotionEvent.ACTION_DOWN:
         mLastX = mCurrX;
         mLastY = mCurrY;
         break;
      default:
         break;
      }
      invalidate();
      return true; //必须返回true
}
}