创建新的 CanvasView

Question

我是编程初学者...所以也许这个问题对你来说听起来很有趣。 我在 MainActivity 中创建一个新的 CanvasView 时遇到问题，因为它的括号内写了一些东西。 这是我的 MainActivity：

public class MainActivity extends AppCompatActivity {
    CanvasView myView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        //the line below doesnt work
        myView = new CanvasView();
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    public void button1(View v){
        CanvasView.l = 400;
        myView.invalidate();
    }
}

这是我的 CanvasView：

public class CanvasView extends View{
    Paint paint = new Paint();
    static int l = 500;

    public CanvasView (Context context, AttributeSet attrs) {
        super(context);
        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setColor(Color.GREEN);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeJoin(Paint.Join.ROUND);
        paint.setStrokeWidth(10);
    }
    @Override
    public void onDraw(final Canvas canvas) {
        canvas.drawLine(100,100,l,100,paint);
    }
}

Answer 1

在 super.onCreate 和 setContentView 之后创建你的画布，如下所示

super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); myView = new CanvasView();