图像视图空指针异常

我试图能够移动'长颈鹿'图像视图。看起来好像是从strings.xml调用资源的方式有问题，或者它继续作为giraffe.setOnTouchListener（this）;上的NullPointerException返回。下面是代码：图像视图空指针异常

public class MainGameActivity extends Activity implements OnTouchListener { 

float x,y,dx,dy; 
ImageView giraffe; 


@Override 
protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     this.requestWindowFeature(Window.FEATURE_NO_TITLE); 
     ImageView giraffe = (ImageView)findViewById(R.id.giraffe); 
     setContentView(R.layout.activity_main_game); 
     giraffe.setOnTouchListener(this); 
} 


public boolean onTouch(View v, MotionEvent me){ 
    switch(me.getAction()){ 
     case MotionEvent.ACTION_DOWN: 
     { 
      x = me.getX(); 
      y = me.getY(); 
      dx = x - giraffe.getX(); 
      dy = y - giraffe.getY(); 
     } 
     break; 
     case MotionEvent.ACTION_MOVE : 
     { 
      giraffe.setX(me.getX()-dx); 
      giraffe.setY(me.getY()-dy); 
     } 
     break; 
    } 
    return 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.activity_main_game, menu); 
    return true; 
}

}

<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=".MainGameActivity" > 

<ImageView 
    android:id="@+id/giraffe" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentBottom="true" 
    android:layout_centerHorizontal="true" 
    android:layout_marginBottom="58dp" 
    android:contentDescription="@string/giraffe" 
    android:src="@drawable/giraffeicon" />

<?xml version="1.0" encoding="utf-8"?>

<string name="app_name">Falling Objects</string> 
<string name="menu_settings">Settings</string> 
<string name="splash_text">Start dodging in:</string> 
<string name="splash_number_countdown" > </string> 
<string name="title_activity_main_game" > </string> 
<string name="version">Version 1.0</string> 
<string name="giraffe">Giraffe</string> 
<string name="s_and_b_productions">Created by: S&amp;B Productions</string> 
<drawable name="giraffe">#F00</drawable>

07-05 19:41:52.006: E/AndroidRuntime(1826): FATAL EXCEPTION: main 
07-05 19:41:52.006: E/AndroidRuntime(1826): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.SandBProductions.fallingobjects/com.SandBProductions.fallingobjects.MainGameActivity}: java.lang.NullPointerException 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at android.app.ActivityThread.access$600(ActivityThread.java:141) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at android.os.Handler.dispatchMessage(Handler.java:99) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at android.os.Looper.loop(Looper.java:137) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at android.app.ActivityThread.main(ActivityThread.java:5039) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at java.lang.reflect.Method.invokeNative(Native Method) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at java.lang.reflect.Method.invoke(Method.java:511) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at dalvik.system.NativeStart.main(Native Method) 
07-05 19:41:52.006: E/AndroidRuntime(1826): Caused by: java.lang.NullPointerException 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at com.SandBProductions.fallingobjects.MainGameActivity.onCreate(MainGameActivity.java:24) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at android.app.Activity.performCreate(Activity.java:5104) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 
07-05 19:41:52.006: E/AndroidRuntime(1826):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)

来源

2013-07-05 Brian

请提供例外的logcat的设置内容视图。 – zmbq

您需要在findViewById之前设置ContentView，否则该活动不知道在哪里寻找。

来源

2013-07-05 19:52:19

aha非常感谢你......这样一个小小的修复...... – Brian

不客气，请记住接受答案，如果它解决了你的问题 –

这个代码是错误的：

ImageView giraffe = (ImageView)findViewById(R.id.giraffe); 
setContentView(R.layout.activity_main_game);

你必须调用SetContentView()之前任何一个布局元素的搜索。这部分应该是

setContentView(R.layout.activity_main_game); 
ImageView giraffe = (ImageView)findViewById(R.id.giraffe);

来源

2013-07-05 19:52:49

尝试：

setContentView(R.layout.activity_main_game); 
ImageView giraffe = (ImageView)findViewById(R.id.giraffe); 
     giraffe.setOnTouchListener(new OnTouchListener() { 
    public boolean onTouch(View v, MotionEvent me){ 
    switch(me.getAction()){ 
     case MotionEvent.ACTION_DOWN: 
     { 
      x = me.getX(); 
      y = me.getY(); 
      dx = x - giraffe.getX(); 
      dy = y - giraffe.getY(); 
     } 
     break; 
     case MotionEvent.ACTION_MOVE : 
     { 
      giraffe.setX(me.getX()-dx); 
      giraffe.setY(me.getY()-dy); 
     } 
     break; 
    } 
    return true; 
} 
});

您需要致电前的ImageView的

来源

2013-07-05 19:55:43 BlackHatSamurai

图像视图空指针异常

回答

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