java - Android : java. lang.NullPointerException 无法启动 Activity

Question

我知道这个问题被问了很多次，但答案总是针对特定的代码。

所以，我正在创建一个游戏，我需要在 Activity 之间切换，我已经尝试了一切，但我的 logcat 总是给我这个错误，模拟器说“应用程序已停止工作”。所以请帮我找出错误。

我的代码是:

MainActivity.java

package com.example.experiment;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class MainActivity extends Activity
{

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView playG=(TextView)findViewById(R.id.playGame);
        playG.setOnClickListener(new View.OnClickListener()
        {   
            @Override
            public void onClick(View arg0)
            {
                Intent i=new Intent(MainActivity.this,GameActivity.class);
                startActivity(i);
            }
        });
    }
}

GameActivity.java

package com.example.experiment;

import android.app.Activity;
import android.os.Bundle;

public class GameActivity extends Activity 
{
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(new Game(this));
    }
}

游戏.java

package com.example.experiment;

import java.util.Random;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Toast;

public class Game extends View 
{
int i=0,j=0;
int hei=0,wid=0,div=0;
int MoUp=0,MoUpDo=0,Rd;
float TouchXU=0,TouchYU=0,TouchXD=0,TouchYD=0;
float CirX,CirY;
int Score=0;
boolean MoveUp=false,Move=false,NextObs=false;
Path Rpath=new Path();
Paint paint=new Paint();
String ScoreStr="";
Random Rand=new Random();
Activity act=new Activity();
GamEnd g=new GamEnd(getContext());
Context context1=act.getApplicationContext();
Intent intent=new Intent();
public Game(Context context)
{
    super(context);
}
@Override
public void onDraw(Canvas canvas)
{
    Rd=Rand.nextInt(10);
    super.onDraw(canvas);
    paint.setAntiAlias(true);
    setBackgroundColor(Color.parseColor("#3E8E21"));
    MainPath(canvas);
    Obstacle1(canvas);
    Ball(canvas);
    Scores(canvas);
}
public void Ball(Canvas canvas)
{
    CirX=getWidth()/2;
    CirY=(getHeight()/2+getHeight()/4);
    paint.setStyle(Paint.Style.STROKE);
    paint.setColor(Color.BLUE);
    paint.setStyle(Paint.Style.FILL);
    if(i<9)
    {
        postInvalidateDelayed(40);
        canvas.drawCircle(CirX, CirY+i, 30, paint);
        i+=3;
        Score+=10;
    }
    else if(MoveUp==true)
    {
        if(MoUp<200)
        {
            postInvalidateDelayed(30);
            canvas.drawCircle(CirX, CirY+i-MoUp, 30, paint);
            MoUp+=40;
            Score+=10;
        }
        else
        {
            postInvalidateDelayed(25);
            canvas.drawCircle(CirX, CirY+i-j+MoUpDo-MoUp, 30, paint);
            MoUpDo+=40;
            Score+=10;
            if(MoUpDo==200) 
            {
                MoUp=0;
                MoUpDo=0;
                MoveUp=false;
            }
        }
    }
    else
    {
        postInvalidateDelayed(40);
        canvas.drawCircle(CirX, CirY+i-j, 30, paint);
        j+=3;
        Score+=10;
        if(j==9) 
        {
            i=0;
            j=0;
        }
    }
    if(hei>=CirY-15 && hei<=CirY+10 && MoveUp==false)
    {
        Toast.makeText(getContext(), "You Are Out", Toast.LENGTH_LONG).show();
        Intent in=new Intent(getContext(),MainActivity.class);
        act.startActivity(in);
    }
}
public void MainPath(Canvas canvas)
{
    paint.setColor(Color.parseColor("#EE874B"));
    paint.setStyle(Paint.Style.FILL);
    Rpath.moveTo(getWidth()/2-getWidth()/6,0);
    Rpath.lineTo(getWidth()/2+getWidth()/6,0);
    Rpath.lineTo(getWidth()/2+getWidth()/3,getHeight());
    Rpath.lineTo(getWidth()/2-getWidth()/3,getHeight());
    Rpath.lineTo(getWidth()/2-getWidth()/6,0);
    canvas.drawPath(Rpath, paint);
    Rpath.reset();
}
@Override
public boolean onTouchEvent(MotionEvent event)
{
    switch(event.getAction())
    {
    case MotionEvent.ACTION_DOWN:
        TouchXD=(float)event.getRawX();
        TouchYD=(float)event.getRawY();
        break;
    case MotionEvent.ACTION_UP:
        TouchXU=(float)event.getRawX();
        TouchYU=(float)event.getRawY();
        break;
    case MotionEvent.ACTION_MOVE:
        Move=true;
        break;
    }
    if(TouchYD>TouchYU && Move==true)
    {
        MoveUp=true;
        Move=false;
    }
    return true;
}
public void Scores(Canvas canvas)
{
    paint.setColor(Color.parseColor("#4CB028"));
    paint.setTextSize(20);
    paint.setTextSkewX((float) 0.1);
    paint.setFakeBoldText(true);
    ScoreStr=String.valueOf(Score);
    canvas.drawText(ScoreStr, 10, 30, paint);
}
public void Obstacle1(Canvas canvas)
{
    paint.setColor(Color.BLACK);
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeWidth(20);
    canvas.drawLine(getWidth()/2-getWidth()/6-wid, hei, getWidth()/2+getWidth()/6+wid, hei, paint);
    float heiDiv=getHeight()/40;
    float widDiv=(getWidth()/3-getWidth()/6)/40;
    wid+=widDiv;
    hei+=heiDiv;
    if(hei>=getHeight())
    {
        NextObs=true;
        hei=0;
        wid=0;
        Obstacle1(canvas);
    }
}
public void ShowEnd(Canvas canvas)
{
    setBackgroundColor(Color.parseColor("#003366"));
    canvas.drawColor(Color.BLACK);
}
}

我的日志猫

08-21 08:57:09.647: E/AndroidRuntime(1253): FATAL EXCEPTION: main
08-21 08:57:09.647: E/AndroidRuntime(1253): Process: com.example.experiment, PID: 1253
08-21 08:57:09.647: E/AndroidRuntime(1253): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.experiment/com.example.experiment.GameActivity}: java.lang.NullPointerException
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.os.Handler.dispatchMessage(Handler.java:102)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.os.Looper.loop(Looper.java:136)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.app.ActivityThread.main(ActivityThread.java:5017)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at java.lang.reflect.Method.invokeNative(Native Method)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at java.lang.reflect.Method.invoke(Method.java:515)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at dalvik.system.NativeStart.main(Native Method)
08-21 08:57:09.647: E/AndroidRuntime(1253): Caused by: java.lang.NullPointerException
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:109)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at com.example.experiment.Game.<init>(Game.java:31)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at com.example.experiment.GameActivity.onCreate(GameActivity.java:12)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.app.Activity.performCreate(Activity.java:5231)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
08-21 08:57:09.647: E/AndroidRuntime(1253):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
08-21 08:57:09.647: E/AndroidRuntime(1253):     ... 11 more

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.experiment"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk
    android:minSdkVersion="11"
    android:targetSdkVersion="19" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="com.example.experiment.MainActivity"
        android:configChanges="orientation"
        android:label="@string/app_name"
        android:screenOrientation="portrait"
        android:theme="@android:style/Theme.NoTitleBar.Fullscreen" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name="com.example.experiment.GameActivity"
        android:label="@string/title_activity_game" >
        <meta-data 
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.experiment.GameActivity"/>
    </activity>
</application>

</manifest>

请各位 friend 帮忙。 提前致谢。

Answer 1

Intent i = new Intent(MainActivity.this, GameActivity.class);

应在

之后声明

super.onCreate();