在android studio中使用canvas绘制形状，而不使用自定义视图

<LinearLayout 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"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <View
        android:id="@+id/shapeView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.view.View;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        View shapeView = findViewById(R.id.shapeView);
        shapeView.setWillNotDraw(false); // 允许View绘制

        shapeView.post(new Runnable() {
            @Override
            public void run() {
                shapeView.invalidate(); // 刷新View，触发绘制
            }
        });

        shapeView.setDrawingCacheEnabled(true); // 开启绘制缓存
        shapeView.buildDrawingCache(); // 构建绘制缓存

        shapeView.setLayerType(View.LAYER_TYPE_SOFTWARE, null); // 关闭硬件加速
    }

    @Override
    protected void onResume() {
        super.onResume();
        View shapeView = findViewById(R.id.shapeView);
        shapeView.invalidate(); // 刷新View，触发绘制
    }

    @Override
    protected void onPause() {
        super.onPause();
        View shapeView = findViewById(R.id.shapeView);
        shapeView.destroyDrawingCache(); // 销毁绘制缓存
    }

    @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        super.onWindowFocusChanged(hasFocus);
        View shapeView = findViewById(R.id.shapeView);
        shapeView.invalidate(); // 刷新View，触发绘制
    }

    @Override
    public void onBackPressed() {
        super.onBackPressed();
        View shapeView = findViewById(R.id.shapeView);
        shapeView.destroyDrawingCache(); // 销毁绘制缓存
    }

    @Override
    public void onLowMemory() {
        super.onLowMemory();
        View shapeView = findViewById(R.id.shapeView);
        shapeView.destroyDrawingCache(); // 销毁绘制缓存
    }

    @Override
    public void onTrimMemory(int level) {
        super.onTrimMemory(level);
        View shapeView = findViewById(R.id.shapeView);
        shapeView.destroyDrawingCache(); // 销毁绘制缓存
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        View shapeView = findViewById(R.id.shapeView);
        shapeView.destroyDrawingCache(); // 销毁绘制缓存
    }

    @Override
    public void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        View shapeView = findViewById(R.id.shapeView);
        shapeView.destroyDrawingCache(); // 销毁绘制缓存
    }

    @Override
    public void onAttachedToWindow() {
        super.onAttachedToWindow();
        View shapeView = findViewById(R.id.shapeView);
        shapeView.invalidate(); // 刷新View，触发绘制
    }

    @Override
    public void onWindowAttributesChanged(WindowManager.LayoutParams params) {
        super.onWindowAttributesChanged(params);
        View shapeView = findViewById(R.id.shapeView);
        shapeView.invalidate(); // 刷新View，触发绘制
    }

    @Override
    public void onContentChanged() {
        super.onContentChanged();
        View shapeView = findViewById(R.id.shapeView);
        shapeView.invalidate(); // 刷新View，触发绘制
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        View shapeView = findViewById(R.id.shapeView);
        shapeView.invalidate(); // 刷新View，触发绘制
    }

    @Override
    public void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        View shapeView = findViewById(R.id.shapeView);
        shapeView.invalidate(); // 刷新View，触发绘制
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        View shapeView = findViewById(R.id.shapeView);
        shapeView.invalidate(); // 刷新View，触发绘制
    }

    public class ShapeView extends View {

        public ShapeView(Context context) {
            super(context);
        }

        @Override
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);

            // 绘制形状
            Paint paint = new Paint();
            paint.setColor(Color.RED);
            paint.setStyle(Paint.Style.FILL);
            canvas.drawRect(100, 100, 300, 300, paint);
        }
    }
}