浅析Android位置权限以及数组寻找索引的坑

LocationManager locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
if(locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)){
 if(ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
  != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission
  (MainActivity.this, Manifest.permission.ACCESS_COARSE_LOCATION)
  != PackageManager.PERMISSION_GRANTED){
 // request permissions
 // ...
 // ...
 }else{  
 Location location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER;
 if(location != null){ 
  double latitude = location.getLatitude(); 
  double longitude = location.getLongitude(); 
 } 
 }
}

spinner.setAdapter(adapter);
　　spinner.setSelection(2);

spinner.setAdapter(adapter);
　　spinner.setSelection(2,true); //spinner会重新layout

 spinner.setAdapter(adapter);![](https://images2018.cnblogs.com/blog/758949/201807/758949-20180726224508174-131546620.jpg)

　　adapter.notifyDataSetChanged(); //通知spinner刷新数据
 spinner.setSelection(2);

<?xml version="1.0" encoding="utf-8"?>
<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"
 tools:context="com.example.sharpcj.helloworld.MainActivity">

 <Spinner
  android:id="@+id/sp_test"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_centerInParent="true">

 </Spinner>

</RelativeLayout>

package com.example.sharpcj.helloworld;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.Spinner;

import java.util.Arrays;

public class MainActivity extends AppCompatActivity {

 private Spinner mSpTest;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  String[] strs = new String[20];
  for (int i = 0; i < strs.length; i++) {
   strs[i] = "第" + i + "项";
  }
  mSpTest = findViewById(R.id.sp_test);
  mSpTest.setAdapter(new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, strs));

  int index = Arrays.binarySearch(strs, "第11项");
  mSpTest.setSelection(index);
 }
}

 // Like public version, but without range checks.
 private static int binarySearch0(Object[] a, int fromIndex, int toIndex,
          Object key) {
  int low = fromIndex;
  int high = toIndex - 1;

  while (low <= high) {
   int mid = (low + high) >>> 1;
   @SuppressWarnings("rawtypes")
   Comparable midVal = (Comparable)a[mid];
   @SuppressWarnings("unchecked")
   int cmp = midVal.compareTo(key);

   if (cmp < 0)
    low = mid + 1;
   else if (cmp > 0)
    high = mid - 1;
   else
    return mid; // key found
  }
  return -(low + 1); // key not found.
 }