雷达扫描

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看了一个学习视频，仿着做了一个效果如下：

思路：用自定义的View来嵌套。画四个不同半径的空心圆，再画一个渐变的实心圆，利用矩阵和线程让他转起来，其中矩阵要注意reset()，不然会叠加。

所有代码，在下面贴出来，其中过程的注解也很清晰：

xml：

<FrameLayout 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"    tools:context=".MainActivity" >  <span style="color:#ff0000;"><strong>  <com.example.leidasm.RadarView</strong></span>        android:layout_width="match_parent"        android:layout_height="match_parent"        android:background="@drawable/alv"<strong><span style="color:#ff0000;"> /></span></strong>    <ImageView        android:layout_width="100dp"        android:layout_height="100dp"        android:layout_gravity="center"        android:src="@drawable/girl" /></FrameLayout>

MainActivity:

package com.example.leidasm;import android.os.Bundle;import android.app.Activity;import android.view.Menu;import android.view.Window;import android.view.WindowManager;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);<span style="color:#ff6666;">//去掉标题栏和信息栏</span><span style="color:#3333ff;">requestWindowFeature(Window.FEATURE_NO_TITLE);getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN);</span>setContentView(R.layout.activity_main);}}

View:

package com.example.leidasm;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Matrix;import android.graphics.Paint;import android.graphics.Paint.Style;import android.graphics.Shader;import android.graphics.SweepGradient;import android.os.Handler;import android.util.AttributeSet;import android.view.View;public class RadarView extends View {private int w,h;private Paint paint,paint2;private Matrix matrix;;private Handler handler=new Handler();//线程选中private Runnable run=new Runnable() {<span style="color:#ff0000;">int i=0;</span>@Overridepublic void run() {<span style="color:#ff6666;">i++;</span>matrix.postRotate(i%360, w/2, h/2);<span style="color:#33cc00;">RadarView.this.invalidate();//更新界面--调用onDraw()</span>handler.postDelayed(run, 10);//UI更新要用handler}};public RadarView(Context context, AttributeSet attrs) {super(context, attrs);//屏幕宽度和高度w=context.getResources().getDisplayMetrics().widthPixels;h=context.getResources().getDisplayMetrics().heightPixels;//画笔1paint=new Paint();paint.setColor(Color.WHITE);paint.setAntiAlias(true);//抗锯齿，光滑paint.setStrokeWidth(4);//宽度paint.setStyle(Style.<span style="color:#ff6666;">STROKE</span>);//空心//画笔2paint2=new Paint();paint2.setColor(Color.parseColor("#<span style="background-color: rgb(255, 153, 0);">88</span>68d2c4"));paint2.setAntiAlias(true);//抗锯齿，光滑paint2.setStyle(Style.<span style="color:#ff6666;">FILL</span>);//实心<span style="color:#3333ff;">Shader shader=new SweepGradient(w/2, h/2, Color.TRANSPARENT, Color.parseColor("#AA68d2c4"));paint2.setShader(shader);//渐变</span>matrix=new Matrix();//初始化矩阵//启动线程handler.post(run);}/** * 画圈和实心圆,转起来 */@Overrideprotected void onDraw(Canvas canvas) {//画出四个空心圈for(int i=1;i<=4;i++){canvas.drawCircle(w/2, h/2, i*(h/8), paint);}//让实心圆转起来canvas.concat(matrix);//画出渐变实心圆canvas.drawCircle(w/2, h/2, h/2, paint2);matrix.reset();//避免矩阵叠加，越转越快}}

invalidate()的解释：

void android.view.View.invalidate()

public void invalidate()

Added in API level 1

Invalidate the whole view. If the view is visible, onDraw(android.graphics.Canvas) will be called at some point in the future. This must be called from a UI thread. To call from a non-UI thread, call postInvalidate().

即：

调用invalidate()便会调用onDraw()方法。

1.线程----》invalidate()

2.非线程--》postInvalidate()

项目下载地址：http://download.csdn.net/detail/fangjingjingll/9420985

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