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需求：PopupWindow 在弹出的时候需要设置背景为半透明状态，写个简单的工具类，方法如下：

public class MainActivity extends AppCompatActivity {
       private PopupWindow mPop;    @Override    protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        findViewById(R.id.but).setOnClickListener(new View.OnClickListener() {
               @Override            public void onClick(View view) {
                   showPop();            }        });    }    private void showPop(){
           WindowUtil.lucencyBackground(this);        View contentView = LayoutInflater.from(this).inflate(R.layout.pop,null);        if (mPop == null){
               mPop = new PopupWindow(contentView,ViewGroup.LayoutParams.WRAP_CONTENT,ViewGroup.LayoutParams.WRAP_CONTENT,true);        }        mPop.setBackgroundDrawable(new BitmapDrawable());        mPop.setContentView(contentView);        mPop.setOutsideTouchable(true);        mPop.showAtLocation(this.getWindow().getDecorView(), Gravity.CENTER, 0, 0);        mPop.setOnDismissListener(new PopupWindow.OnDismissListener() {
               @Override            public void onDismiss() {
                   mPop.dismiss();                WindowUtil.cancelBackground(MainActivity.this);            }        });    }}public static void lucencyBackground(Activity activity) {
           WindowManager.LayoutParams lp = activity.getWindow().getAttributes();        lp.alpha = 0.3f;        activity.getWindow().addFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);        activity.getWindow().setAttributes(lp);    }    public static void cancelBackground(Activity activity) {
           WindowManager.LayoutParams lp1 = activity.getWindow().getAttributes();        lp1.alpha = 1f;        activity.getWindow().clearFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);        activity.getWindow().setAttributes(lp1);    }源码连接

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