Android学习笔记画笔和画布

概念

• 画笔类:Paint用于指定颜色、透明度、笔触磅数、图形样式。
• 画布类:Canvas用于指定背景颜色，尺寸画笔的容器。

绘图的基本步骤

继承View类，重写OnDraw()——>在Activity中引用

案例绘制一个矩形

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/framelayout"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
</FrameLayout>

MyView.java

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.view.View;

public class MyView extends View {
    public MyView(Context context) {
        super(context);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint = new Paint(); //定义一个默认的画笔
        paint.setColor(0xFFFF6600);
        paint.setStyle(Paint.Style.FILL);//设置填充方式
        canvas.drawRect
                (10,10,280,150,paint);
        //绘制矩形
    }
}

MainActivity.java

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.FrameLayout;

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        FrameLayout frameLayout = findViewById(R.id.framelayout);
        frameLayout.addView(new MyView(this));

    }
}

效果: