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我知道原因可能是我沒有引用具有Id的正確佈局。但是，我確定他們的Id在相應的佈局中。我收到這個錯誤，因爲我開始包含警報對話框，這是由inflater引起的嗎？感謝這裏的幫助。即使在檢查佈局引用後仍然無法解析NullPointerException
我試圖做什麼的簡要概述：我的主要活動是有3個片段的viewpager。我主要工作在第一個片段，片段main。在發佈時，應用程序將要求一個新的玩家名稱，然後將該數據傳輸給玩家類。我的按鈕只是打開一個對話框，顯示與創建的「newplayer」相關的詳細信息。希望這可以幫助。
package fantasy.myapplication;
import android.app.Dialog;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.View;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import cn.pedant.SweetAlert.SweetAlertDialog;
import fantasy.myapplication.Fragments.fragment_army;
import fantasy.myapplication.Fragments.fragment_main;
import fantasy.myapplication.Fragments.fragment_treasures;
import fantasy.myapplication.player.player;
public class MainActivity extends AppCompatActivity {
private SectionsPagerAdapter mSectionsPagerAdapter;
private ViewPager mViewPager;
private TabLayout tabLayout;
public player thisplayer;
public String playerID;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.activity_main);
final Button btn_playerinfo = (Button) findViewById(R.id.btnplayerid);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayShowTitleEnabled(false);
toolbar.setTitle("");
toolbar.setSubtitle("");
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(mViewPager);
mViewPager.setCurrentItem(2);
//Setup Player
View popup_newplayer = (LayoutInflater.from(MainActivity.this)).inflate(R.layout.popup_newplayer,null);
AlertDialog.Builder alert_newplayer = new AlertDialog.Builder(MainActivity.this);
alert_newplayer.setView(popup_newplayer);
final EditText newplayerid = (EditText) popup_newplayer.findViewById(R.id.tb_newplayer);
Button btn_newplayer_create = (Button) popup_newplayer.findViewById(R.id.btn_newplayer_ok);
Button btn_newplayer_cancel = (Button) popup_newplayer.findViewById(R.id.btn_newplayer_cancel);
final Dialog dialog_newplayer = alert_newplayer.create();
dialog_newplayer.show();
btn_newplayer_create.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
dialog_newplayer.dismiss();
playerID = newplayerid.getText().toString();
thisplayer = new player(playerID);
btn_playerinfo.setText(newplayerid.getText());
new SweetAlertDialog(MainActivity.this, SweetAlertDialog.SUCCESS_TYPE)
.setTitleText("Success!")
.setContentText("New player "+playerID+" created!")
.show();
}
});
btn_newplayer_cancel.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
dialog_newplayer.dismiss();
}
});
btn_playerinfo.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//Display Player Info
View popup_playerinfo = (LayoutInflater.from(MainActivity.this)).inflate(R.layout.popup_playerinfo,null);
AlertDialog.Builder alert_playerinfo = new AlertDialog.Builder(MainActivity.this);
alert_playerinfo.setView(popup_playerinfo);
TextView playerinfo_id = (TextView) popup_playerinfo.findViewById(R.id.info_playerid);
playerinfo_id.setText(newplayerid.getText());
final Dialog dialog_playerinfo = alert_playerinfo.create();
dialog_playerinfo.show();
}
});
}
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) { super(fm);}
@Override
public Fragment getItem(int position) {
//return the current tabs
switch (position) {
case 0:
return new fragment_army();
case 1:
return new fragment_treasures();
case 2:
return new fragment_main();
default:
return null;
}
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Army";
case 1:
return "Treasures";
case 2:
return "Main";
}
return null;
}
@Override
public int getCount() {return 3;}
}
這是我的主要片段XML代碼：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/main_bg">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Main page"
android:id="@+id/textView"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Player ID"
android:id="@+id/btnplayerid"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="26dp"
android:textSize="10dp" />
</RelativeLayout>
這是activity_main XML
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="fantasy.myapplication.MainActivity"
android:id="@+id/main_activity">
<android.support.v7.widget.Toolbar
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:id="@+id/toolbar"
android:background="?attr/colorPrimary"
android:layout_alignParentBottom="true">
</android.support.v7.widget.Toolbar>
<android.support.design.widget.TabLayout
android:id="@+id/tabs"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
app:tabIndicatorColor="#ffffff"
app:tabGravity="fill"/>
<android.support.v4.view.ViewPager
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
android:layout_above="@id/tabs"/>
</RelativeLayout>
我的片段
類package fantasy.myapplication.Fragments;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import fantasy.myapplication.R;
public class fragment_main extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}
這是錯誤消息：顯示java.lang.NullPointerException：嘗試上的空對象引用 –
btn_playerinfo.setText調用虛擬方法「無效android.widget.Button.setText（java.lang.CharSequence中）」（newplayerid.getText （））;嘗試將此行更改爲btn_playerinfo.setText（newplayerid.getText（）。toSting（））; –
將'btn_playerinfo'更改爲實例級變量 –