这里的画直线不是通过新建一个View类,在View的画布中画,而是直接在activity中画。
package lizm.lt;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.Menu;
import android.widget.LinearLayout;
import android.widget.TextView;
public class MainActivity extends Activity {
private LinearLayout mylayout;
private TextView tt;
private Bitmap bitmap;
private int x=0, y=0, xx=800, yy=480;
Paint paint;
Canvas canvas;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mylayout = (LinearLayout)findViewById(R.id.myLayout);
tt = (TextView)findViewById(R.id.myText);
paint = new Paint();
paint.setStrokeWidth(5);//笔宽5像素
paint.setColor(Color.RED);//设置为红笔
// paint.setAntiAlias(false);//锯齿不显示
bitmap = Bitmap.createBitmap(800, 480, Bitmap.Config.ARGB_8888); //设置位图的宽高,bitmap为透明
canvas = new Canvas(bitmap);
canvas.drawColor(Color.TRANSPARENT,PorterDuff.Mode.CLEAR);//设置为透明,画布也是透明
canvas.drawLine(0, 20, 750, 200, paint);
//在画布上贴张小图
Bitmap bm = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
canvas.drawBitmap(bm, 0, 0, paint);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));//橡皮擦一样擦除
canvas.drawLine(0, 20, 750, 200, paint);
paint.setXfermode(null);//取消擦除模式
paint.setColor(Color.BLUE);
canvas.drawLine(0, 20, 750, 200, paint);
Drawable drawable = new BitmapDrawable(bitmap) ;
mylayout.setBackgroundDrawable(drawable);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
// TODO Auto-generated method stub
if(keyCode == 19){
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));//橡皮擦一样擦除
canvas.drawLine(x, y, xx, yy, paint);
x +=20;
y +=20;
xx-=20;
yy-=20;
paint.setXfermode(null);//取消擦除模式
paint.setColor(Color.BLUE);
canvas.drawLine(x, y, xx, yy, paint);
Drawable drawable = new BitmapDrawable(bitmap) ;
mylayout.setBackgroundDrawable(drawable);
}
return super.onKeyDown(keyCode, event);
}
}
运行效果,如下,每按一次方向上键,就擦除上一条直线,重画另一条直线
