我不确定为什么会收到此错误，它以前是有效的，我们将不胜感激。尝试在微调器选择时产生一个新 Activity (我有一个内部有 ListView 的工作版本，我决定分支尝试微调器，走了很远然后迷路了试图找出这个错误)。它也工作得很好，所以我知道我必须像 1-5 行代码之类的。再次感谢您的帮助。
日志
02-19 23:57:15.980: E/AndroidRuntime(350): FATAL EXCEPTION: main
02-19 23:57:15.980: E/AndroidRuntime(350): java.lang.RuntimeException: Unable to instantiate activity
ComponentInfo{com.example.jordanmaxportfolio/com.example.jordanmaxportfolio.MainActivity}: java.lang.NullPointerException
02-19 23:57:15.980: E/AndroidRuntime(350): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1569)
02-19 23:57:15.980: E/AndroidRuntime(350): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
02-19 23:57:15.980: E/AndroidRuntime(350): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
02-19 23:57:15.980: E/AndroidRuntime(350): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
02-19 23:57:15.980: E/AndroidRuntime(350): at android.os.Handler.dispatchMessage(Handler.java:99)
02-19 23:57:15.980: E/AndroidRuntime(350): at android.os.Looper.loop(Looper.java:123)
02-19 23:57:15.980: E/AndroidRuntime(350): at android.app.ActivityThread.main(ActivityThread.java:3683)
主要 Activity
package com.example.jordanmaxportfolio;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Spinner;
import android.widget.TextView;
public class MainActivity extends Activity
implements AdapterView.OnItemSelectedListener {
TextView selection;
ListView list;
Spinner spin = (Spinner) findViewById(R.id.spinner2);
public final static String exID="com.example.portfolio.MainActivity";
static final String[] items = new String[] {
"36-2510 Game Engine Scripting I",
"36-2551 C++ I",
"36-3210 Game AI Programming",
"36-3405 Authoring Interactive Media I & II"
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
list = (ListView)findViewById(R.id.listView1);
String[] items = getResources().getStringArray(R.array.Classes);
list.setAdapter(new ArrayAdapter<String>(MainActivity.this,android.R.layout.simple_list_item_1,items));
list.setOnItemClickListener(new OnItemClickListener(){
public void onItemClick(AdapterView<?> parent, View view,
int postion, long id){
Intent i =new Intent(MainActivity.this,ClassPage.class);
i.putExtra(exID, String.valueOf(id));
startActivity(i);
}
});
selection = (TextView) findViewById(R.id.textView1);
Spinner spin = (Spinner) findViewById(R.id.spinner2);
spin.setOnItemSelectedListener(this);
ArrayAdapter<String> aa = new ArrayAdapter<String>(
this,
android.R.layout.simple_spinner_item,
items);
aa.setDropDownViewResource(
android.R.layout.simple_spinner_dropdown_item);
spin.setAdapter(aa);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
public void onItemSelected(AdapterView<?> parent, View v, int position,
long id) {
// TODO Auto-generated method stub
selection.setText(items[position]);
Intent i =new Intent(MainActivity.this,ClassPage.class);
i.putExtra(exID, String.valueOf(position));
startActivity(i);
}
/*spin.setOnItemSelectedListener(new OnItemSelectedListener()
{
@Override
public void onItemSelected(AdapterView<?> parent, View v, int position,
long id) {
Intent i =new Intent(MainActivity.this,ClassPage.class);
i.putExtra(exID, String.valueOf(id));
startActivity(i);
@Override
public void onNothingSelected(AdapterView<?> parent) {
// TODO Auto-generated method stub
}
}
});*/
/* example I saw online, however not quite right */
public void onNothingSelected(AdapterView<?> parent) {
// TODO Auto-generated method stub
selection.setText("");
}
}
类页面
package com.example.jordanmaxportfolio;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.support.v4.app.NavUtils;
import android.annotation.TargetApi;
import android.content.Intent;
import android.os.Build;
public class ClassPage extends Activity {
private TextView passedView = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_class);
String passedVar = getIntent().getStringExtra(MainActivity.exID);
passedView = (TextView)findViewById(R.id.tv1);
//passedView.setText("You have clicked item id: "+passedVar);
if(passedVar.equals("0"))
{
passedView.setText("YAYY");
}
if(passedVar.equals("1"))
{
passedView.setText("Game Engine Scripting I");
ImageView iv = (ImageView)findViewById(R.id.imageView1);
iv.setImageResource(R.drawable.asteroids);
TextView tv2 = (TextView)findViewById(R.id.tv2);
tv2.setText("Using C# and Unity, I created a remake of the classic 'Asteroids!'. Dynamic difficulty level is the next addition.");
}
else if(passedVar.equals("2"))
{
passedView.setText("C++ I");
ImageView iv = (ImageView)findViewById(R.id.imageView1);
iv.setImageResource(R.drawable.poker);
TextView tv2 = (TextView)findViewById(R.id.tv2);
tv2.setText("Console GUI C++ Texas Hole 'Em Poker created by Neil Inglese and Jordan Max. Basic concept of game was to eliminate cursors. The game was completed, however we are re-doing it for our C++ II class to make it into the Xbox Live and Windows Store.");
}
else if(passedVar.equals("3"))
{
passedView.setText("Game AI Programming");
ImageView iv = (ImageView)findViewById(R.id.imageView1);
iv.setImageResource(R.drawable.game);
TextView tv2 = (TextView)findViewById(R.id.tv2);
tv2.setText("Currently enrolled in this class, we are learning about FSM's and C++ data structures such as stacks, vectors and queues. ");
}
else
{
passedView.setText("Authoring Interactive Media I & II");
ImageView iv = (ImageView)findViewById(R.id.imageView1);
iv.setImageResource(R.drawable.p);
TextView tv2 = (TextView)findViewById(R.id.tv2);
tv2.setText("Learned basic skills for HTML and CSS. Also divulged into HTML5, PHP, jQuery, and Javascript for web programming. Created my portfolio website based off knowledge learned.");
}
Button btn1 = (Button)findViewById(R.id.button1);
// Show the Up button in the action bar.
setupActionBar();
}
public void btnClicked(View view){
Intent i = new Intent(this,MainActivity.class);
startActivity(i);
}
/**
* Set up the {@link android.app.ActionBar}, if the API is available.
*/
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
private void setupActionBar() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
getActionBar().setDisplayHomeAsUpEnabled(true);
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.class_page, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This ID represents the Home or Up button. In the case of this
// activity, the Up button is shown. Use NavUtils to allow users
// to navigate up one level in the application structure. For
// more details, see the Navigation pattern on Android Design:
//
// http://developer.android.com/design/patterns/navigation.html#up-vs-back
//
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
}
acitvity_class.xml
<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".ClassPage" >
<TextView
android:id="@+id/tv1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:text="@string/hello_world" />
<ImageView
android:id="@+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="200dp"
android:layout_alignLeft="@+id/tv1"
android:layout_alignRight="@+id/tv1"
android:layout_below="@+id/tv1"
android:layout_marginTop="46dp"
android:maxHeight="500dp"
android:src="@drawable/ic_launcher" />
<TextView
android:id="@+id/tv2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/imageView1"
android:layout_alignParentRight="true"
android:layout_below="@+id/imageView1"
android:layout_marginLeft="21dp"
android:layout_marginTop="60dp"
android:text="TextView" />
<Button
android:id="@+id/button1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignRight="@+id/tv2"
android:layout_below="@+id/tv2"
android:layout_marginTop="20dp"
android:onClick="btnClicked"
android:text="Go Back" />
</RelativeLayout>
activity_main.xml
<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
<ListView
android:id="@+id/listView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/spinner1" >
</ListView>
<Spinner
android:id="@+id/spinner1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/textView1"
android:layout_marginTop="67dp"
android:layout_toLeftOf="@+id/listView1" />
<TextView
android:id="@+id/textView2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/textView1"
android:layout_below="@+id/textView1"
android:text="@string/hello" />
<Spinner
android:id="@+id/spinner2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/textView2"
android:layout_below="@+id/textView2"
android:layout_marginLeft="57dp" />
</RelativeLayout>
最佳答案
放这个
Spinner spin = (Spinner) findViewById(R.id.spinner2);
在 setContentView(R.layout.activity_main); 之后的 onCreate() 内；
关于java - 不确定为什么会抛出 NullPointer，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21899543/