Java 将文本视图添加到布局时的NullPointerException
将TextView添加到LinearLayout时,生成的是NullPointerException。我叫这个Java 将文本视图添加到布局时的NullPointerException,java,android,android-layout,Java,Android,Android Layout,将TextView添加到LinearLayout时,生成的是NullPointerException。我叫这个 public void loadPlayers() { LinearLayout lv = (LinearLayout) findViewById(R.id.player_list); TextView tv = new TextView(this); for (int i = 0; i < Game.getPlayers().length; i++)
public void loadPlayers() {
LinearLayout lv = (LinearLayout) findViewById(R.id.player_list);
TextView tv = new TextView(this);
for (int i = 0; i < Game.getPlayers().length; i++) {
tv.setText(String.valueOf(Game.getPlayers()[i]));
tv.setPadding(8, 8, 8, 8);
tv.setTextSize(20);
tv.setBackgroundColor(0xD0D0D0);
System.out.println("Got here!");
lv.addView(tv);
}
}
但我不明白为什么这是个问题。布局是否尚未加载?如果是,我该如何解决?下面是完整的活动、xml和日志
MainActivity.java:
package com.example.lineupcreator;
import android.app.Activity;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.content.Context;
import android.os.Build;
import android.os.Bundle;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.support.v4.widget.DrawerLayout;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity
implements NavigationDrawerFragment.NavigationDrawerCallbacks {
/* My Methods */
/**
* Adds a player, gets input from button
* @return
*/
public void addPlayer(View view) {
EditText editText = (EditText) findViewById(R.id.edit_message);
String name = editText.getText().toString();
LinearLayout lv = (LinearLayout) findViewById(R.id.player_list);
TextView tv = new TextView(this);
tv.setText(String.valueOf(name));
tv.setPadding(8, 8, 8, 8);
tv.setTextSize(20);
tv.setBackgroundColor(0xD0D0D0);
lv.addView(tv);// not InformationActivity.tv just write tv
Game.newPlayer(name);
}
/**
* Loads all of the players
*/
public void loadPlayers() {
LinearLayout lv = (LinearLayout) findViewById(R.id.player_list);
TextView tv = new TextView(this);
for (int i = 0; i < Game.getPlayers().length; i++) {
tv.setText(String.valueOf(Game.getPlayers()[i]));
tv.setPadding(8, 8, 8, 8);
tv.setTextSize(20);
tv.setBackgroundColor(0xD0D0D0);
System.out.println("Got here!");
lv.addView(tv);
}
}
/* Prebuilt Methods */
/**
* Fragment managing the behaviors, interactions and presentation of the navigation drawer.
*/
private NavigationDrawerFragment mNavigationDrawerFragment;
/**
* Used to store the last screen title. For use in {@link #restoreActionBar()}.
*/
private CharSequence mTitle;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mNavigationDrawerFragment = (NavigationDrawerFragment)
getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
mTitle = getTitle();
// Set up the drawer.
mNavigationDrawerFragment.setUp(
R.id.navigation_drawer,
(DrawerLayout) findViewById(R.id.drawer_layout));
/* My Code */
Game.init();
this.loadPlayers();
}
@Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, PlaceholderFragment.newInstance(position + 1))
.commit();
}
public void onSectionAttached(int number) {
switch (number) {
case 1:
mTitle = getString(R.string.title_section1);
break;
case 2:
mTitle = getString(R.string.title_section2);
break;
case 3:
mTitle = getString(R.string.title_section3);
break;
}
}
public void restoreActionBar() {
ActionBar actionBar = getSupportActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
actionBar.setDisplayShowTitleEnabled(true);
actionBar.setTitle(mTitle);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
if (!mNavigationDrawerFragment.isDrawerOpen()) {
// Only show items in the action bar relevant to this screen
// if the drawer is not showing. Otherwise, let the drawer
// decide what to show in the action bar.
getMenuInflater().inflate(R.menu.main, menu);
restoreActionBar();
return true;
}
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section
* number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
((MainActivity) activity).onSectionAttached(
getArguments().getInt(ARG_SECTION_NUMBER));
}
}
}
编辑:
在我看来,四元数在正确的道路上,但他的解决方案不起作用。我还尝试创建一个文本视图数组,如下图所示,但也没有成功
public void loadPlayers() {
LinearLayout lv = (LinearLayout) findViewById(R.id.player_list);
TextView[] tv = new TextView[Game.getPlayers().length];
for (int i = 0; i < Game.getPlayers().length; i++) {
tv[i] = new TextView(this);
tv[i].setText(String.valueOf(Game.getPlayers()[i]));
tv[i].setPadding(8, 8, 8, 8);
tv[i].setTextSize(20);
tv[i].setBackgroundColor(0xD0D0D0);
System.out.println("Got here!");
lv.addView(tv[i]);
}
}
public void loadPlayers(){
LinearLayout lv=(LinearLayout)findViewById(R.id.player_列表);
TextView[]tv=新的TextView[Game.getPlayers().length];
for(int i=0;i
更新:
我试着从addPlayer而不是onCreate调用LoadPlayer,效果非常好。唯一的问题是从onCreate调用LoadPlayer时产生的。Ok,错误是您正在尝试从主活动中膨胀布局组件,但您正在膨胀片段,因此,您的主布局没有显示在屏幕中,是顶部的片段布局。你需要行动
<LinearLayout
android:id="@+id/player_list"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@android:color/darker_gray"
android:orientation="vertical" />
分割布局
如果这不起作用,请告诉我。我认为您不能多次将同一视图添加到父视图。您需要将新TextView的实例化移动到for循环中 LoadPlayer函数应如下所示:
public void loadPlayers() {
LinearLayout lv = (LinearLayout) findViewById(R.id.player_list);
for (int i = 0; i < Game.getPlayers().length; i++) {
TextView tv = new TextView(this);
tv.setText(String.valueOf(Game.getPlayers()[i]));
tv.setPadding(8, 8, 8, 8);
tv.setTextSize(20);
tv.setBackgroundColor(0xD0D0D0);
System.out.println("Got here!");
lv.addView(tv);
}
}
public void loadPlayers(){
LinearLayout lv=(LinearLayout)findViewById(R.id.player_列表);
for(int i=0;i
希望这有帮助,如果没有,你可能手头有一个更大的问题=(
获取NullPointerException
的原因是,您试图从活动中获取线性布局
,该布局在片段
中膨胀,特别是以下行:
public void loadPlayers() {
LinearLayout lv = (LinearLayout) findViewById(R.id.player_list);
// R.id.player_list is not inside activity_main.xml
// lv is null
...
lv.addView(tv[i]); // NullPointerException
}
}
解决这个问题的一种方法是移动片段中的所有逻辑
LinearLayout lv;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
lv = (LinearLayout) rootView.findViewById(R.id.player_list);
return rootView;
}
在占位符片段
中添加onActivityCreated(Bundle savedInstanceState)
,并将两行从onCreate()
移动到那里。这是为了确保在活动已设置后调用代码
@Override
public void onActivityCreated (Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
/* My Code */
Game.init();
this.loadPlayers();
}
然后将loadPlayers()
移动到占位符片段
内。但是,片段
内没有findViewById()
。相反,您必须初始化onCreateView()
内的视图。不要忘记声明片段
内的变量
LinearLayout lv;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
lv = (LinearLayout) rootView.findViewById(R.id.player_list);
return rootView;
}
最后,Fragment
使用其活动中的上下文
。虽然您可以在活动中使用此
引用其上下文
,但在Fragment
中您不能。相反,请使用getActivity()
public void loadPlayers(){
//LinearLayout lv=(LinearLayout)findViewById(R.id.player_列表);
文本视图电视;
for(int i=0;i
发布的XML文件是片段布局。我应该添加acitivity_main.XML吗?只有一个问题,如果您使用的是片段,为什么要在活动中调用函数??,是否尝试在片段onCreateView()中调用LoadPlayer功能?我不知道。我对android开发和其他引用MainActivity.java文件中片段的方法有点陌生。如果我添加项目布局的图片会有帮助吗?我在问题中添加了文件名。有帮助吗?如果我链接repo@user3586222会有帮助吗?没有。不起作用。试过cre正在打印一个TextView数组,但我仍然收到相同的错误。另一个错误是…尝试只打印第一个播放器,但我仍然收到空指针异常。可能是因为我的布局尚未加载?尝试从活动访问片段视图的典型情况。在片段中执行loadPlayer操作。(或者干脆不要使用片段)如上所述,您将活动
与片段
(对于使用最新开发工具包的新Android开发人员来说非常容易理解)。一个简单的解释是,您正在片段
中设置布局(注意名称fragment\u main.xml
),但您的逻辑在活动
中。两者都没有直接链接,也不能像那样简单。对于初学者,您可以完全忽略使用片段
。在onCreate()
中,更改为setContentView(R.layout.Fragment_main);
(或将内容从fragment\u main.xml
复制到activity\u main.xml
)然后再试一次。@andrewT。将setContentView移动到fragment_main仍然不起作用。如果有帮助,可以在@njzk2找到repo。我理解为什么这可能是个问题,但我在addPlayer上做的几乎是相同的事情。是因为我从片段调用它,它在那里工作,而不是在loadPlayer中工作吗?是因为我用this.loadPlayers调用它时发现它不工作?哦,很抱歉,刚刚意识到activity\u main.xml
中有DrawerLayout
public void loadPlayers() {
LinearLayout lv = (LinearLayout) findViewById(R.id.player_list);
// R.id.player_list is not inside activity_main.xml
// lv is null
...
lv.addView(tv[i]); // NullPointerException
}
}
@Override
public void onActivityCreated (Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
/* My Code */
Game.init();
this.loadPlayers();
}
LinearLayout lv;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
lv = (LinearLayout) rootView.findViewById(R.id.player_list);
return rootView;
}
public void loadPlayers() {
// LinearLayout lv = (LinearLayout) findViewById(R.id.player_list);
TextView tv;
for (int i = 0; i < Game.getPlayers().length; i++) {
tv = new TextView(getActivity());
tv.setText(String.valueOf(Game.getPlayers()[i].getName()));
tv.setPadding(8, 8, 8, 8);
tv.setTextSize(20);
tv.setBackgroundColor(0xD0D0D0);
lv.addView(tv);
}
}