android画等边三角形

运行截图如下图所示

1.画三角形类

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Bitmap.Config;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class Triangle extends View {
 private int mStartX;
 private int mStartY;
 private Path mPath;
 private Paint mPaint;
 private float point_x_3;
 private float point_y_3;
 private float point_x_2;
 private float point_y_2;
 int VIEW_WIDTH = 1280;
 int VIEW_HEIGHT = 750;
 // 定义一个内存中的图片，该图片将作为缓冲区
 Bitmap cacheBitmap ;
 // 定义cacheBitmap上的Canvas对象
 Canvas cacheCanvas = null;

 public Triangle(Context context, AttributeSet attrs) {
  super(context, attrs);
  
  mPath = new Path();
  mPaint = new Paint();
  
  cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH, VIEW_HEIGHT,
    Config.ARGB_8888);
  cacheCanvas = new Canvas();
  
  //设置画笔的颜色
  mPaint.setColor(Color.YELLOW);
  //设置背景色
  cacheBitmap.eraseColor(Color.RED);
  
  // 设置cacheCanvas将会绘制到内存中的cacheBitmap上
  cacheCanvas.drawBitmap(cacheBitmap, VIEW_WIDTH, VIEW_HEIGHT, null);
  mPaint.setStrokeWidth(10);
  mPaint.setAntiAlias(true);
  // 设置Paint的样式
  mPaint.setStyle(Paint.Style.STROKE);
  // 设置结合处为圆弧
  mPaint.setStrokeJoin(Paint.Join.ROUND);
  // 设置画笔样式为圆弧
  mPaint.setStrokeCap(Paint.Cap.ROUND);
 }

 @Override
 public boolean onTouchEvent(MotionEvent event) {

  switch (event.getAction()) {
  case MotionEvent.ACTION_DOWN:
   mStartX = (int) event.getX();
   mStartY = (int) event.getY();
   break;
  case MotionEvent.ACTION_MOVE:
   float x = event.getX();
   float y = event.getY();
   float deltaX = x - mStartX;
   float deltaY = y - mStartY;
   float frac = (float) Math.sqrt(3) / 2;
   point_x_2 = x;
   point_y_2 = y;
   point_x_3 = mStartX + (float) (Math.sqrt(1 - Math.pow(frac, 2)) * deltaX - frac * deltaY);
   point_y_3 = mStartY + (float) (Math.sqrt(1 - Math.pow(frac, 2)) * deltaY + frac * deltaX);
   break;
  case MotionEvent.ACTION_UP:
   mPath.reset(); 
   mPath.moveTo(mStartX, mStartY);
   mPath.lineTo(point_x_2, point_y_2);
   mPath.lineTo(point_x_3, point_y_3);
   mPath.close();
   
   break;
  default:
   break;
  }
  invalidate();
  return true;
 }

 @Override
 protected void onDraw(Canvas canvas) {
  canvas.drawPath(mPath, mPaint);
 }
}

 

2.activity类

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class MainActivity extends Activity {

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

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater().inflate(R.menu.main, menu);
  return true;
 }

}

3.布局文件

<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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >
 
    <com.mmmm.sanjiaox.Triangle
        android:layout_height="fill_parent"
        android:layout_width="fill_parent"
        android:width="1280dp"
  android:height="1280dp"
        />
</RelativeLayout>