android开发 JAVA知识点

1.Intent.putExtra()实现活动间通信

Intent intent = new Intent();
intent.setClass(MainActivity.this,ShowTrack.class);
intent.putExtra(LocateDbAdapter.TRACKID,track_id);
startActivity(intent);

Intent intent = getIntent();
BaseBundle extras = intent.getExtras();
if (extras != null) {
    track_id = extras.getInt(LocateDbAdapter.TRACKID);

2.LocationManager.requestLocationUpdates()需要验证，不能直接使用

if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED){
    lm.requestLocationUpdates(LocationManager.NETWORK_PROVIDER,0,0,locationListener);
}

3.cursor默认指向-1，使用前需要moveToFirst()