Android Canvas 随机停止在屏幕上绘图

Question

我遇到了一个问题，如果我们继续重新启动应用程序，画布会随机停止在屏幕上绘制。

我已经通过记录器检查了方法onDraw() 正在被调用。但我在设备上的手指痕迹不可见。

任何帮助和建议表示赞赏。 干杯

Answer 1

你可以试试这个代码在屏幕上画线或更多......

包com.kk.demo；

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PointF;
import android.os.Bundle;
import android.util.FloatMath;
import android.util.Log;
import android.view.Display;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class ZoomDemoActivity extends Activity implements OnTouchListener {
     ImageView imageView;
      Bitmap bitmap;
      Canvas canvas;
      Paint paint;

      float downx = 0,downy = 0,upx = 0,upy = 0;

      @Override
      public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        imageView = (ImageView) this.findViewById(R.id.imageView1);
        Display currentDisplay = getWindowManager().getDefaultDisplay();
        float dw = currentDisplay.getWidth();
        float dh = currentDisplay.getHeight();

        bitmap = Bitmap.createBitmap((int) dw, (int) dh,
            Bitmap.Config.ARGB_8888);
        canvas = new Canvas(bitmap);
        paint = new Paint();
        paint.setColor(Color.GREEN);
        imageView.setImageBitmap(bitmap);
        imageView.setOnTouchListener(this);
      }

      public boolean onTouch(View v, MotionEvent event) {
        int action = event.getAction();
        switch (action) {
        case MotionEvent.ACTION_DOWN:
          downx = event.getX();
          downy = event.getY();
          break;
        case MotionEvent.ACTION_MOVE:
          upx = event.getX();
          upy = event.getY();
          canvas.drawLine(downx, downy, upx, upy, paint);
          imageView.invalidate();
          downx = upx;
          downy = upy;
          break;
        case MotionEvent.ACTION_UP:
          upx = event.getX();
          upy = event.getY();
          canvas.drawLine(downx, downy, upx, upy, paint);
          imageView.invalidate();
          break;
        case MotionEvent.ACTION_CANCEL:
          break;
        default:
          break;
        }
        return true;
      }
    }