findViewById返回null

Question

我正在制作一个应用程序应该是一个非常简单的街头霸王版本，实际上只需轻扫一下即可，AI可以踢或打，然后健康就会被取消。我只是试图让健康部分失效，但每次我刷程序退出，我的TextView得到一个空指针异常。起初我认为问题是我在一个没有使用setContentView方法的类中使用了findViewById，但是当我将它移动到MainActivity类时，我仍然遇到同样的错误。与此主题相关的其他问题已经说过setContentView方法指向不同的布局，但是这个确定指向正确的布局。这是GameView类，MainActivity类和activity_main xml文件。

GameView：

package com.example.images;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.TextView;

@SuppressWarnings({"unused" })
public class GameView extends SurfaceView implements SurfaceHolder.Callback {
    private GameThread thread;
    private Animation a;
    private EnemyAnim ea;
    private int count = 0;
    private float down, up;
    private Character ryu, chun_li;
    private TextView r,l;

    public GameView(Context context) {
        super(context);
        up = 0;
        down = 0;
        getHolder().addCallback(this);
        thread = new GameThread(getHolder(), this, context);
        // animation = new Animation(100,100);
        a = new Animation(context);
        ea = new EnemyAnim(context);
        ryu = new Character(1000);
        chun_li = new Character(1000);
        r = MainActivity.r;
        l = MainActivity.l;

        setFocusable(true);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        thread.setRunning(true);
        thread.start();

    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {

    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width,
            int height) {

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        String attack;
        double action = Math.random();
        if (action >= .5) {
            attack = "kick";
        }
        else {
            attack = "punch";
        }
        switch(event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            down = event.getY();

        case MotionEvent.ACTION_UP:
            up = event.getY();
        }

        if (down < up && Math.abs(down-up)>=20) {
            a.setAnimation("punch");
            chun_li.act("punch");
        }
        else if (down > up && Math.abs(down-up)>=20) {
            a.setAnimation("kick");
            chun_li.act("kick");
        }
        ea.setAnimation(attack);
        ryu.act(attack);
        r.setText(ryu.getHealth());
        l.setText(chun_li.getHealth());
        return true;
    }

    @Override
    public void onDraw(Canvas canvas) {
        try {
            canvas.drawColor(Color.BLACK);
            a.getCurrentFrame().draw(canvas);
            ea.getCurrentFrame().draw(canvas);
        } 
        catch (NullPointerException e) {
            return;
        }
        //count++;
    }
}

MainActivity：

package com.example.images;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.widget.TextView;

@SuppressWarnings("all")
public class MainActivity extends FragmentActivity {
    public static TextView r,l;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        r = (TextView)findViewById(R.id.ryu_health);
        l = (TextView)findViewById(R.id.li_health);

    }
}

activity_main.xml中：

<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"
    tools:context="com.example.images.MainActivity" >

    <TextView
        android:id="@+id/ryu_health"
        android:layout_width="200dp"
        android:layout_height="100dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:text="Ryu health: 1000"
        android:gravity="left|center"
        android:textColor="@android:color/black" />

    <fragment
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        class="com.example.images.FragmentThing" />

    <TextView
        android:id="@+id/li_health"
        android:layout_width="200dp"
        android:layout_height="100dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:gravity="right|center"
        android:text="Chun-Li health: 1000"
        android:textColor="@android:color/black" />

</RelativeLayout>

错误日志：

08-13 11:05:52.671: E/AndroidRuntime(7997): FATAL EXCEPTION: main
08-13 11:05:52.671: E/AndroidRuntime(7997): Process: com.example.images, PID: 7997
08-13 11:05:52.671: E/AndroidRuntime(7997): java.lang.NullPointerException
08-13 11:05:52.671: E/AndroidRuntime(7997):     at com.example.images.GameView.onTouchEvent(GameView.java:84)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.View.dispatchTouchEvent(View.java:8107)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2411)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2101)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2411)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2101)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2411)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2101)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2411)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2101)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2411)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2101)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2280)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1615)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.app.Activity.dispatchTouchEvent(Activity.java:2544)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2228)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.View.dispatchPointerEvent(View.java:8315)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4597)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4465)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4023)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4077)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4046)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4157)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4054)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4214)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4023)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4077)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4046)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4054)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4023)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6404)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6308)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6279)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6244)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6484)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.os.MessageQueue.nativePollOnce(Native Method)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.os.MessageQueue.next(MessageQueue.java:138)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.os.Looper.loop(Looper.java:123)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at android.app.ActivityThread.main(ActivityThread.java:5356)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at java.lang.reflect.Method.invokeNative(Native Method)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at java.lang.reflect.Method.invoke(Method.java:515)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
08-13 11:05:52.671: E/AndroidRuntime(7997):     at dalvik.system.NativeStart.main(Native Method)