Java 访问TextView时获取NullPointerException
我正在尝试从java中的布局访问textview。在访问它时,我在日志猫中得到NullPointerException。这是我的密码Java 访问TextView时获取NullPointerException,java,android,android-service,Java,Android,Android Service,我正在尝试从java中的布局访问textview。在访问它时,我在日志猫中得到NullPointerException。这是我的密码 public class GameActivity extends Activity { TextView tv = (TextView)findViewById(R.id.ctry); /** Called when the activity is first created. */ @Override public void onCreate(Bundle
public class GameActivity extends Activity {
TextView tv = (TextView)findViewById(R.id.ctry);
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tv.setText("Text");
}
}
这是我的日志
05-20 12:32:57.808: D/AndroidRuntime(18776): Shutting down VM
05-20 12:32:57.808: W/dalvikvm(18776): threadid=1: thread exiting with uncaught exception (group=0x4001e578)
05-20 12:32:57.808: E/AndroidRuntime(18776): FATAL EXCEPTION: main
05-20 12:32:57.808: E/AndroidRuntime(18776): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.zafar.game/com.zafar.game.GameActivity}: java.lang.NullPointerException
05-20 12:32:57.808: E/AndroidRuntime(18776): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1573)
05-20 12:32:57.808: E/AndroidRuntime(18776): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
05-20 12:32:57.808: E/AndroidRuntime(18776): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
05-20 12:32:57.808: E/AndroidRuntime(18776): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
05-20 12:32:57.808: E/AndroidRuntime(18776): at android.os.Handler.dispatchMessage(Handler.java:99)
05-20 12:32:57.808: E/AndroidRuntime(18776): at android.os.Looper.loop(Looper.java:130)
05-20 12:32:57.808: E/AndroidRuntime(18776): at android.app.ActivityThread.main(ActivityThread.java:3691)
05-20 12:32:57.808: E/AndroidRuntime(18776): at java.lang.reflect.Method.invokeNative(Native Method)
05-20 12:32:57.808: E/AndroidRuntime(18776): at java.lang.reflect.Method.invoke(Method.java:507)
05-20 12:32:57.808: E/AndroidRuntime(18776): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
05-20 12:32:57.808: E/AndroidRuntime(18776): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
05-20 12:32:57.808: E/AndroidRuntime(18776): at dalvik.system.NativeStart.main(Native Method)
05-20 12:32:57.808: E/AndroidRuntime(18776): Caused by: java.lang.NullPointerException
05-20 12:32:57.808: E/AndroidRuntime(18776): at android.app.Activity.findViewById(Activity.java:1653)
05-20 12:32:57.808: E/AndroidRuntime(18776): at com.zafar.game.GameActivity.<init>(GameActivity.java:11)
05-20 12:32:57.808: E/AndroidRuntime(18776): at java.lang.Class.newInstanceImpl(Native Method)
05-20 12:32:57.808: E/AndroidRuntime(18776): at java.lang.Class.newInstance(Class.java:1409)
05-20 12:32:57.808: E/AndroidRuntime(18776): at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
05-20 12:32:57.808: E/AndroidRuntime(18776): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1565)
05-20 12:32:57.808: E/AndroidRuntime(18776): ... 11 more
05-20 12:32:57.808:D/AndroidRuntime(18776):关闭虚拟机
05-20 12:32:57.808:W/dalvikvm(18776):threadid=1:线程以未捕获异常退出(组=0x4001e578)
05-20 12:32:57.808:E/AndroidRuntime(18776):致命异常:主
05-20 12:32:57.808:E/AndroidRuntime(18776):java.lang.RuntimeException:无法实例化活动组件信息{com.zafar.game/com.zafar.game.GameActivity}:java.lang.NullPointerException
05-20 12:32:57.808:E/AndroidRuntime(18776):在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1573)
05-20 12:32:57.808:E/AndroidRuntime(18776):在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
05-20 12:32:57.808:E/AndroidRuntime(18776):在android.app.ActivityThread.access$1500(ActivityThread.java:117)
05-20 12:32:57.808:E/AndroidRuntime(18776):在android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
05-20 12:32:57.808:E/AndroidRuntime(18776):在android.os.Handler.dispatchMessage(Handler.java:99)上
05-20 12:32:57.808:E/AndroidRuntime(18776):在android.os.Looper.loop(Looper.java:130)
05-20 12:32:57.808:E/AndroidRuntime(18776):位于android.app.ActivityThread.main(ActivityThread.java:3691)
05-20 12:32:57.808:E/AndroidRuntime(18776):位于java.lang.reflect.Method.Invokenactive(本机方法)
05-20 12:32:57.808:E/AndroidRuntime(18776):位于java.lang.reflect.Method.invoke(Method.java:507)
05-20 12:32:57.808:E/AndroidRuntime(18776):位于com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
05-20 12:32:57.808:E/AndroidRuntime(18776):位于com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
5-20 12:32:57.808:E/AndroidRuntime(18776):在dalvik.system.NativeStart.main(本机方法)
05-20 12:32:57.808:E/AndroidRuntime(18776):由以下原因引起:java.lang.NullPointerException
05-20 12:32:57.808:E/AndroidRuntime(18776):在android.app.Activity.findViewById(Activity.java:1653)
05-20 12:32:57.808:E/AndroidRuntime(18776):位于com.zafar.game.GameActivity。(GameActivity.java:11)
05-20 12:32:57.808:E/AndroidRuntime(18776):位于java.lang.Class.newInstanceImpl(本机方法)
05-20 12:32:57.808:E/AndroidRuntime(18776):位于java.lang.Class.newInstance(Class.java:1409)
05-20 12:32:57.808:E/AndroidRuntime(18776):在android.app.Instrumentation.newActivity(Instrumentation.java:1021)上
05-20 12:32:57.808:E/AndroidRuntime(18776):在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1565)
05-20 12:32:57.808:E/AndroidRuntime(18776):。。。还有11个
只有在调用setContentView(R.layout.main)
后,才能调用findViewById(R.id.ctry)
在onCreate()
code中不能调用
TextView tv = (TextView)findViewById(R.id.ctry);
以前
setContentView
上线后
setContentView(R.layout.main);
使用like
public class GameActivity extends Activity {
TextView tv;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tv = (TextView)findViewById(R.id.ctry);
tv.setText("Text");
}
}
更新
在main.xml中
<Button android:id="@+id/match" ... />
您能看到我的更新吗?为什么在上面的第二个代码中会出现相同的错误?打开main.xml,看到您有一个带有match
id的按钮?查看我的最新答案
<Button android:id="@+id/match" ... />