我是Android编程新手,只有一点java背景。出于某种原因,我在基于The New Bostons Android Tutorial系列制作的程序中的3个类创建了类似于此的错误:
03-13 18:17:22.095: E/AndroidRuntime(13055): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.infitenothing.dogcat/com.infitenothing.word.OpenClass}: java.lang.NullPointerException
03-13 18:17:22.095: E/AndroidRuntime(13055): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
03-13 18:17:22.095: E/AndroidRuntime(13055): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
03-13 18:17:22.095: E/AndroidRuntime(13055): at android.app.ActivityThread.access$800(ActivityThread.java:135)
03-13 18:17:22.095: E/AndroidRuntime(13055): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
03-13 18:17:22.095: E/AndroidRuntime(13055): at android.os.Handler.dispatchMessage(Handler.java:102)
03-13 18:17:22.095: E/AndroidRuntime(13055): at android.os.Looper.loop(Looper.java:136)
03-13 18:17:22.095: E/AndroidRuntime(13055): at android.app.ActivityThread.main(ActivityThread.java:5017)
03-13 18:17:22.095: E/AndroidRuntime(13055): at java.lang.reflect.Method.invokeNative(Native Method)
03-13 18:17:22.095: E/AndroidRuntime(13055): at java.lang.reflect.Method.invoke(Method.java:515)
03-13 18:17:22.095: E/AndroidRuntime(13055): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-13 18:17:22.095: E/AndroidRuntime(13055): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
03-13 18:17:22.095: E/AndroidRuntime(13055): at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:126)
03-13 18:17:22.095: E/AndroidRuntime(13055): at dalvik.system.NativeStart.main(Native Method)
03-13 18:17:22.095: E/AndroidRuntime(13055): Caused by: java.lang.NullPointerException
03-13 18:17:22.095: E/AndroidRuntime(13055): at com.infitenothing.word.OpenClass.intalize(OpenClass.java:43)
03-13 18:17:22.095: E/AndroidRuntime(13055): at com.infitenothing.word.OpenClass.onCreate(OpenClass.java:29)
03-13 18:17:22.095: E/AndroidRuntime(13055): at android.app.Activity.performCreate(Activity.java:5231)
03-13 18:17:22.095: E/AndroidRuntime(13055): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
03-13 18:17:22.095: E/AndroidRuntime(13055): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
03-13 18:17:22.095: E/AndroidRuntime(13055): ... 12 more
我使用此类启动活动
public class Menu extends ListActivity {
String classes[] = {"MainActivity", "Splash", "TextPlay", "Email", "Camera", "DatA", "OpenClass", "example1", "example1"};
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setListAdapter(new ArrayAdapter<String>(Menu.this, android.R.layout.simple_list_item_1, classes ));
}
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
// TODO Auto-generated method stub
super.onListItemClick(l, v, position, id);
String cheese = classes[position];
try{
Class ourClass = Class.forName("com.infitenothing.word." + cheese);
Intent ourIntent = new Intent(Menu.this, ourClass);
startActivity(ourIntent);
}catch(ClassNotFoundException e){
e.printStackTrace();
}
}
}
这些是无效的课程
package com.infitenothing.word;
import com.infitenothing.dogcat.R;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class Data extends Activity implements OnClickListener {
Button start, startFor;
TextView gotAnswer;
EditText sendET;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
intalize();
setContentView(R.layout.get);
}
private void intalize() {
start = (Button) findViewById(R.id.bSA);
startFor = (Button) findViewById(R.id.bSAFR);
gotAnswer = (TextView) findViewById(R.id.tvGot);
sendET= (EditText) findViewById(R.id.etSend);
start.setOnClickListener(this);
startFor.setOnClickListener(this);
}
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
switch (arg0.getId()){
case R.id.bSA:
String bread = sendET.getText().toString();
Bundle basket = new Bundle();
basket.putString("key", bread);
Intent a = new Intent(Data.this, OpenClass.class);
a.putExtras(basket);
startActivity(a);
break;
case R.id.bSAFR:
break;
}
}
}
和
package com.infitenothing.word;
import java.util.Random;
import com.infitenothing.dogcat.R;
import android.R.anim;
import android.R.integer;
import android.R.string;
import android.app.Activity;
import android.graphics.Color;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.support.v4.widget.SimpleCursorAdapter.ViewBinder;
import android.text.InputType;
import android.view.Gravity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.ToggleButton;
public class TextPlay extends Activity implements View.OnClickListener {
Button chkCmd;
ToggleButton passTog;
EditText input;
TextView display;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.text);
baconAndEggs();
passTog.setOnClickListener(this);
chkCmd.setOnClickListener(this);
}
private void baconAndEggs() {
// TODO Auto-generated method stub
Button chkCmd = (Button) findViewById(R.id.bResults);
passTog = (ToggleButton) findViewById(R.id.tbPassword);
input = (EditText) findViewById(R.id.etCommands);
display = (TextView) findViewById(R.id.tvResults);
}
@Override
public void onClick(View view) {
// TODO Auto-generated method stub
switch (view.getId()) {
case R.id.bResults:
// TODO Auto-generated method stub
String check = input.getText().toString();
if (check.contentEquals("left") || check.contentEquals("Left")) {
display.setText("LEFT!!!");
display.setGravity(Gravity.LEFT);
} else if (check.contentEquals("center")
|| check.contentEquals("Center")) {
display.setText(check + " !!!");
display.setGravity(Gravity.CENTER);
} else if (check.contentEquals("right")
|| check.contentEquals("Right")) {
display.setText("Ha Ha you have been tricked");
display.setGravity(Gravity.LEFT);
} else if (check.contentEquals("blue")
|| check.contentEquals("Blue")) {
display.setText("Yellow");
display.setTextColor(Color.BLUE);
display.setTextSize(50);
} else if (check.contentEquals("role")) {
// Random
// Way one (created by me) Num choser
/*
* double joe = Math.random(); double crazy = joe *100; int cast
* = (int) crazy; display.setText("" + cast);
*/
// Way two Travis
Random crazyRandom = new Random();
display.setText("Dice???????!!!!!!");
display.setTextSize(crazyRandom.nextInt(200));
display.setTextColor(Color.rgb(crazyRandom.nextInt(256),
crazyRandom.nextInt(256), crazyRandom.nextInt(256)));
// Switch Travis
switch (crazyRandom.nextInt(3)) {
case 0:
display.setGravity(Gravity.LEFT);
break;
case 1:
display.setGravity(Gravity.CENTER);
break;
case 2:
display.setGravity(Gravity.RIGHT);
break;
}
} else if (check.contentEquals("cat")) {
MediaPlayer meow = MediaPlayer
.create(TextPlay.this, R.raw.meow);
display.setText("I am the most evil cat");
meow.start();
} else {
display.setGravity(Gravity.CENTER);
display.setTextColor(Color.WHITE);
display.setText("invalid");
}
break;
case R.id.tbPassword:
if (passTog.isChecked() == true) {
input.setInputType(InputType.TYPE_CLASS_TEXT
| InputType.TYPE_TEXT_VARIATION_PASSWORD);
} else {
input.setInputType(InputType.TYPE_CLASS_TEXT);
}
break;
}
}
}
最后
package com.infitenothing.word;
import com.infitenothing.dogcat.R;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.RadioGroup;
import android.widget.RadioGroup.OnCheckedChangeListener;
import android.widget.TextView;
public class OpenClass extends Activity implements OnClickListener,
OnCheckedChangeListener {
TextView question, test;
Button returnData;
RadioGroup selectList;
String gotBread;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.send);
intalize();
/*
* Bundle gotBasket = getIntent().getExtras(); gotBread =
* gotBasket.getString("key"); question.setText(gotBread);
*/
}
private void intalize() {
// TODO Auto-generated method stub
question = (TextView) findViewById(R.id.tvQestion);
question = (TextView) findViewById(R.id.tvQestion);
selectList = (RadioGroup) findViewById(R.id.rgAnswer);
selectList.setOnCheckedChangeListener(this);
returnData.setOnClickListener(this);
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
@Override
public void onCheckedChanged(RadioGroup group, int checkedId) {
// TODO Auto-generated method stub
// check id ma not be right vabable
switch (checkedId) {
case R.id.rcrazy:
break;
case R.id.rawsome:
break;
case R.id.rBoth:
break;
}
}
}
我的机器人清单是
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.infitenothing.dogcat"
android:versionCode="1"
android:versionName="1.0009" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="18" />
<permission android:name="android.permission.SET_WALLPAPER"></permission>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.infitenothing.word.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.infitenothing.word.MainActivity" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.infitenothing.word.Menu"
android:label="SPLASH" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.infitenothing.word.Splash"
android:label="SPLASH" >
<intent-filter>
<action android:name="com.infitenothing.word.Splash" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.infitenothing.word.Magic"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.infitenothing.word.Magic" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.infitenothing.word.TextPlay"
android:label="@string/app_name" >
</activity>
<activity
android:name="com.infitenothing.word.Email"
android:label="@string/app_name" >
</activity>
<activity
android:name="com.infitenothing.word.Camera"
android:label="Camera to Wallpaper"
android:screenOrientation="portrait"
>
</activity>
<activity
android:name="com.infitenothing.word.Data"
android:label="Camera to Wallpaper"
android:screenOrientation="portrait"
>
<intent-filter>
<action android:name="com.infitenothing.word.Data" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.infitenothing.word.OpenClass"
android:label="Camera to Wallpaper"
android:screenOrientation="portrait"
>
</activity>
</application>
</manifest>
很抱歉这篇文章很长,但我一直在寻找一段时间,并没有找到任何解决这个问题的好答案。
解决此问题的任何答案都将是一个巨大的帮助
答案 0 :(得分:1)
您正在按钮上调用setOnClickListener方法:
returnData.setOnClickListener(this);
但您之前从未初始化此按钮! ==&GT; NPE
要解决此问题,您需要像使用其他视图一样使用findViewById:
returnData = (Button) findViewById(R.id.the_id_of_your_button);