在RelativeLayout中绘制从角到角的对角线

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;
import android.widget.RelativeLayout;

public class DiagonalLineView extends View {
    private Paint paint;

    public DiagonalLineView(Context context) {
        super(context);
        init();
    }

    public DiagonalLineView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public DiagonalLineView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        paint = new Paint();
        paint.setColor(Color.BLACK);
        paint.setStrokeWidth(5);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int width = getWidth();
        int height = getHeight();
        canvas.drawLine(0, 0, width, height, paint);
    }
}

<RelativeLayout 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">

    <com.example.myapplication.DiagonalLineView
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <!-- 其他视图组件 -->

</RelativeLayout>