判断是否是第一次进入

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        firstRun();
    }

private void firstRun() {
    SharedPreferences sharedPreferences = getSharedPreferences("FirstRun",0);
    Boolean firstrun = sharedPreferences.getBoolean("First",true);
    if (firstrun){
        sharedPreferences.edit().putBoolean("First",false).commit();
        Toast.makeText(this,"第一次",Toast.LENGTH_LONG).show();
    }
    else {
        Toast.makeText(this,"不是第一次",Toast.LENGTH_LONG).show();
    }
}