关于java：如何在Android Studio中将类添加到AndroidManifest.xml文件？

How to add a class to AndroidManifest.xml file in Android Studio?

本问题已经有最佳答案，请猛点这里访问。

我从Eclipse切换到Android Studio，我正在尝试将一个活动添加到我的清单文件中，我不知道应该使用什么代码，我的应用程序不断崩溃，这是我清单中的代码。

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<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="penis.jason.payday">

<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme">
<activity
android:name=".MainActivity"
android:label="@string/app_name">
<intent-filter>

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>

<activity android:name="settings"
android:label="Pay Day!!">

</activity>

<activity android:name="statistics"
android:label="Pay Day!!">

</activity>

</application>

我让它做的是当用户按下设置按钮时，它会把它带到这个类和新的XML中。这是我用来发送意图的代码

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Settings.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent GoToSettings = new Intent(getApplicationContext(), settings.class);

startActivity(GoToSettings);
finish();
}
});

这是我的落袋猫

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08-24 10:41:52.098 21750-21750/penis.jason.payday E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: penis.jason.payday, PID: 21750
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{penis.jason.payday/penis.jason.payday.settings}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2259)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392)
at android.app.ActivityThread.access$900(ActivityThread.java:169)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1280)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5487)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.app.Activity.findViewById(Activity.java:1986)
at penis.jason.payday.settings.<init>(settings.java:23)
at java.lang.Class.newInstanceImpl(Native Method)
at java.lang.Class.newInstance(Class.java:1208)
at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2250)

这是整个设置类

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package penis.jason.payday;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.CheckBox;

import java.util.Calendar;

@SuppressWarnings("unused")
public class settings extends Activity {

boolean FullScreen;

Button SaveAndExit = (Button) findViewById(R.id.SaveAndExit);
Button Save = (Button) findViewById(R.id.Save);
Button Cls = (Button) findViewById(R.id.Cls);
CheckBox FullScreenOnOff = (CheckBox) findViewById(R.id.fullScreen);
CheckBox SaveWarningOnOff = (CheckBox) findViewById(R.id.SaveWarningOnOff);

Calendar cal = Calendar.getInstance();
int year = cal.get(Calendar.YEAR);
int month= cal.get(Calendar.MONTH)+1;
int day = cal.get(Calendar.DATE);

String FullDate = (""+month+"/"+day+"/"+year);
String Date=(String.valueOf(FullDate));

@Override
protected void onCreate(Bundle saveInstanceState){
super.onCreate(saveInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.settings);

FullScreen = getSharedPreferences("Settings",MODE_PRIVATE).getBoolean("FullScreen",false);
if(FullScreen==true){
this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.settings);
}

SaveAndExit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent GoToMain = new Intent(getApplicationContext(), MainActivity.class);

startActivity(GoToMain);
finish();

}
});

Save.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {

}
});

Cls.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {

}
});

if(FullScreenOnOff.isChecked()){
FullScreen = true;
SharedPreferences FullScreenSave = getSharedPreferences("Settings", Context.MODE_PRIVATE);
SharedPreferences.Editor FullScreenE = FullScreenSave.edit();
FullScreenE.putBoolean("FullScreen", FullScreen);
FullScreenE.commit();
}

}
}

____更新____我发现了问题！

我不得不改变我的按钮变量声明方式

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boolean FullScreen;
Button SaveAndExit,Save,Cls;
CheckBox FullScreenOnOff,SaveWarningOnOff;

Calendar cal = Calendar.getInstance();
int year = cal.get(Calendar.YEAR);
int month= cal.get(Calendar.MONTH)+1;
int day = cal.get(Calendar.DATE);

String FullDate = (""+month+"/"+day+"/"+year);
String Date=(String.valueOf(FullDate));

@Override
protected void onCreate(Bundle saveInstanceState){
super.onCreate(saveInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.settings);

FullScreen = getSharedPreferences("Settings",MODE_PRIVATE).getBoolean("FullScreen",false);
if(FullScreen==true){
this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.settings);
}

SaveAndExit = (Button) findViewById(R.id.SaveAndExit);
Save = (Button) findViewById(R.id.Save);
Cls = (Button) findViewById(R.id.Cls);
FullScreenOnOff = (CheckBox) findViewById(R.id.fullScreen);
SaveWarningOnOff = (CheckBox) findViewById(R.id.SaveWarningOnOff);

}