一、前言
由于最近项目需要，急需开发一个探照灯的功能，限定三天内完成，在网上搜了一整天，尝试各种实现方法，其实无外乎使用BitmapShader和ShapeDrawable在画布上画出源图片，还有一些使用其他语言的方法，比如canavas的clip相关的方法，但是都不能满足我的项目需求。第一个方法虽然可以实现探照灯的效果，缺点是必须要有源图像，而我都项目要求是不管你在哪个界面，都要能够直接探照到背景（就相当于被探照部分变透明了，直接看到后面）。最后只能想办法自己实现了，于是第二天想出了一个可行的方案，如下：
先看下效果图（额....只有静态的，gif不会做）:
Screenshot_2019-07-22-20-10-47-439_com.donview.searchlight.png
Screenshot_2019-07-22-20-10-58-271_com.donview.searchlight.png
Screenshot_2019-07-22-20-11-19-783_com.donview.searchlight.png
旁边的按钮可以调放大镜的大小，每次点击放大镜都会自动聚焦到那个位置的中心。
二、思路
根据需求，总结如下：
-探照灯功能
-探照灯可移动
-探照的部分透明
-在其他应用界面仍然可用
三、实现
废话不多说，直接上代码：
-1.实现Activity透明
在配置文件中给Activity添加如上主题，即将
android:theme="@style/theApp"
改为：
android:theme="@style/TranspantTheme"
这样子启动起来的Activity就是个透明的。
-2.退出应用仍然可用（在其他应用界面仍然可用）
使用WindowManager：
private WindowManager windowManager;
private WindowManager.LayoutParams wmParams,wm;
private int wmType;
private void initView() {
//以下：Window的相关属性设置，可自定义，
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
wmType = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
} else {
wmType = WindowManager.LayoutParams.TYPE_PHONE;
}
windowManager = (WindowManager) this.getSystemService(Context.WINDOW_SERVICE);
wmParams = new WindowManager.LayoutParams();
wmParams.type = wmType;
wmParams.screenOrientation = ActivityInfo.SCREEN_ORIENTATION_SENSOR_LANDSCAPE;
wmParams.flags |= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
wmParams.gravity = Gravity.LEFT | Gravity.TOP;
wmParams.x = 0;
wmParams.y = 0;
wmParams.width = WindowManager.LayoutParams.MATCH_PARENT;
wmParams.height = WindowManager.LayoutParams.MATCH_PARENT;
wmParams.format = PixelFormat.RGBA_8888;
wm = new WindowManager.LayoutParams();
wm.type = wmType;
wm.screenOrientation = ActivityInfo.SCREEN_ORIENTATION_SENSOR_LANDSCAPE;
wm.flags |= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
wm.gravity = Gravity.RIGHT | Gravity.TOP;
wm.x = 0;
wm.y = 0;
wm.width = 100;
wm.height = 100;
wm.format = PixelFormat.RGBA_8888;
}
先初始化好windowManager，别忘了在Activity配置文件中设置为横屏显示（受到windowManager影响）
-3.定义实现探照灯功能的View
直接上代码：
public class MyImageView extends android.support.v7.widget.AppCompatImageView{
private Paint paint1,paint2;//两只笔
private float x=200,y=200;
private int screenWidth,screenHeight;//屏幕宽高，用于判断移动路径是否越界
public MyImageView(Context context) {
super(context);
initData();
}
private synchronized void initData() {
//获取屏幕宽高
DisplayMetrics metrics = getResources().getDisplayMetrics();
screenWidth = metrics.widthPixels;
screenHeight = metrics.heightPixels;
setMyEraseSize(40);
setColor(Color.GRAY);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
drawBackground(canvas);
drawMyCircle(canvas);
}
//画圆
private void drawMyCircle(Canvas canvas) {
canvas.drawCircle(x,y,100,paint1);
}
//画背景颜色
private void drawBackground(Canvas canvas) {
Rect rect=new Rect(0,0,screenWidth,screenHeight);
canvas.drawRect(rect,paint2);//将背景涂满，相当于一块布满屏幕的画布
}
//原理：通过不断改变x,y坐标重绘透明圆，实现探照灯功能，因为Android中的橡皮擦擦除实际上就是用透明笔把原先笔迹覆盖掉
public boolean onTouchEvent(MotionEvent event){
final int x = (int) event.getX();// 获取当前触摸点的X轴坐标
final int y = (int) event.getY(); // 获取当前触摸点的Y轴坐标
this.x=x;this.y=y;
invalidate(); // 重绘画布
return true;
}
//设置橡皮擦大小
public void setMyEraseSize(int size){
paint1= new Paint();
paint1.reset();
paint1.setAntiAlias(true);//抗锯齿
paint1.setDither(true);//防抖动
paint1.setColor(Color.WHITE);
paint1.setStrokeWidth(size);
paint1.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
BlurMaskFilter bmf=new BlurMaskFilter((0.5f), BlurMaskFilter.Blur.SOLID);
paint1.setMaskFilter(bmf);
paint1.setStyle(Paint.Style.FILL);
paint1.setStrokeJoin(Paint.Join.ROUND);
paint1.setStrokeCap(Paint.Cap.ROUND);
paint1.setSubpixelText(true);
paint1.setTextSize(50);
}
//设置比颜色
public void setColor(int color){
paint2=new Paint();
paint2.reset();
paint2.setAntiAlias(true);//抗锯齿
paint2.setDither(true);//防抖动
paint2.setStrokeWidth(5);
paint2.setTextSize(50);
paint2.setSubpixelText(true);
BlurMaskFilter bmf=new BlurMaskFilter((0.5f), BlurMaskFilter.Blur.SOLID);
paint2.setMaskFilter(bmf);
paint2.setPathEffect(new CornerPathEffect(20));
paint2.setStyle(Paint.Style.FILL);
paint2.setStrokeJoin(Paint.Join.ROUND);
paint2.setStrokeCap(Paint.Cap.ROUND);
paint2.setColor(color);
}
}
解析：
简单来说，其实就是采用思路：
用两只笔，一只负责画背景（黑布），一只负责橡皮擦的功能（画圆），这时由于Activity是透明的，所以就可以直接看到下一层内容，然后在手指移动时更新橡皮擦（圆形）的位置，重绘就可以了。代码很简单，相信你能看懂！！
怎么样？是不是很简单？
为了能让大家看到效果，这里接着加上这个demo的其他方法：
public class MainActivity extends Activity {
private WindowManager windowManager;
private WindowManager.LayoutParams wmParams,wm;
private int wmType;
private MyImageView myImageView;
private ImageView view;
private final int OVERLAY_PERMISSION_REQ_CODE = 1234;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (checkBallPermission()) startProgram();
}
//检查是否有悬浮窗权限
private boolean checkBallPermission()
{
if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M)
{
if(!Settings.canDrawOverlays(this)) {
Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:" + getPackageName()));
startActivityForResult(intent,OVERLAY_PERMISSION_REQ_CODE);
return false;
}
}
return true;
}
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
Log.e("SearchPrint","onActivityResult");
if (requestCode == OVERLAY_PERMISSION_REQ_CODE) {
if(android.os.Build.VERSION.SDK_INT>=Build.VERSION_CODES.M) {
if (!Settings.canDrawOverlays(this))
{
Toast.makeText(MainActivity.this, this.getResources().getString(R.string.ballfail), Toast.LENGTH_SHORT).show();
this.finish();
}
else {
startProgram();
}
}
}
}
private void startProgram() {
initView();
show();
addListener();
}
private void addListener() {
//点击关闭按钮退出程序，移除view
view.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
hide();
finish();
}
});
}
private void hide(){
try{
windowManager.removeView(myImageView);
windowManager.removeView(view);
}catch (Exception e){
e.printStackTrace();
Log.e("SearchPrint","removeView:"+e.getMessage());
}
}
private void show() {
try{
windowManager.addView(myImageView,wmParams);
windowManager.addView(view,wm);
}catch (Exception e){
e.printStackTrace();
Log.e("SearchPrint","addView:"+e.getMessage());
}
}
private void initView() {
myImageView=new MyImageView(this);
view=new ImageView(this);
view.setBackgroundResource(R.drawable.exit);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
wmType = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
} else {
wmType = WindowManager.LayoutParams.TYPE_PHONE;
}
windowManager = (WindowManager) this.getSystemService(Context.WINDOW_SERVICE);
wmParams = new WindowManager.LayoutParams();
wmParams.type = wmType;
wmParams.screenOrientation = ActivityInfo.SCREEN_ORIENTATION_SENSOR_LANDSCAPE;
wmParams.flags |= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
wmParams.gravity = Gravity.LEFT | Gravity.TOP;
wmParams.x = 0;
wmParams.y = 0;
wmParams.width = WindowManager.LayoutParams.MATCH_PARENT;
wmParams.height = WindowManager.LayoutParams.MATCH_PARENT;
wmParams.format = PixelFormat.RGBA_8888;
wm = new WindowManager.LayoutParams();
wm.type = wmType;
wm.screenOrientation = ActivityInfo.SCREEN_ORIENTATION_SENSOR_LANDSCAPE;
wm.flags |= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
wm.gravity = Gravity.RIGHT | Gravity.TOP;
wm.x = 0;
wm.y = 0;
wm.width = 100;
wm.height = 100;
wm.format = PixelFormat.RGBA_8888;
}
}
四、其他
如果需要实现探照出来的是一张自定义的图片，那更简单，直接结合使用BitmapShader和ShapeDrawable，网上有不少方法，你还可以添加个从图库里面选择图片的方法，都挺简单的，由于篇幅限制，这里就不再叙述了。
原创文章，转载请加上链接https://www.jianshu.com/p/438e5c7f3ba7