android空指针异常

我写了一个简单的程序，但有问题。 代码如下：

package player.org;

import android.app.Activity;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.animation.AlphaAnimation;
import android.view.animation.Animation;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;

public class Player extends Activity {
    /** Called when the activity is first created. */
    private MediaPlayer media;
    private ProgressBar progress;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tabs);

        progress=(ProgressBar) findViewById(R.id.progress);

       progress.setVisibility(ProgressBar.INVISIBLE);

这是tabs.xml

<?xml version="1.0" encoding="utf-8"?>
    <AbsoluteLayout 
     android:layout_width="fill_parent" 
     android:layout_height="fill_parent" 
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:background="#FFFFFF">
     <ProgressBar
        android:id="@+id/progress"
        android:layout_width="250dp"
        android:layout_height="8dp"
        style="@android:style/Widget.ProgressBar.Horizontal"
        android:layout_x="35dp"
        android:layout_y="320dp"/>
</AbsoluteLayout>

---

请显示stacktrace（来自logcat）在模拟器中启动您的应用程序，并查看logcat（在Eclipse:Window>ShowView>Other…>Android>logcat中）。当你的应用程序崩溃时，stacktrace应该显示在LogCat中——这应该可以帮助你找到崩溃的原因。我查看了日志聊天，这里是“在player.org.player.onCreate（player.java:27）”中的一小部分——你还没有给我们看那段代码。我想那一行是

progress.setVisibility（ProgressBar.INVISIBLE）

，所以问题是

ProgressBar）findViewById（R.id.progress）

不工作，请尝试Project->Clean，然后再次运行它。请显示stacktrace（从logcat）在模拟器中启动应用程序，并查看logcat（在Eclipse:Window>show View>Other…>Android>logcat中）。当您的应用程序崩溃时，stacktrace应该显示在LogCat中--这应该可以帮助您找到崩溃的原因。我查看了日志聊天，这里是“在player.org.player.onCreate（player.java:27）”中的一小部分--您还没有向我们显示该代码。我想这行是

progress.setVisibility（ProgressBar.INVISIBLE）

，所以问题是

进度=（ProgressBar）findViewById（R.id.progress）

不工作，请尝试Project->Clean，然后再次运行它。

08-07 08:24:02.516: ERROR/AndroidRuntime(334): FATAL EXCEPTION: main
08-07 08:24:02.516: ERROR/AndroidRuntime(334): java.lang.RuntimeException: Unable to start activity ComponentInfo{player.org/player.org.Player}: java.lang.NullPointerException
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at android.os.Looper.loop(Looper.java:123)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at android.app.ActivityThread.main(ActivityThread.java:3683)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at java.lang.reflect.Method.invokeNative(Native Method)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at java.lang.reflect.Method.invoke(Method.java:507)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at dalvik.system.NativeStart.main(Native Method)
08-07 08:24:02.516: ERROR/AndroidRuntime(334): Caused by: java.lang.NullPointerException
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at player.org.Player.onCreate(Player.java:26)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
08-07 08:24:02.516: ERROR/AndroidRuntime(334):     ... 11 more
08-07 08:24:02.536: WARN/ActivityManager(67):   Force finishing activity player.org/.Player
08-07 08:24:03.056: WARN/ActivityManager(67): Activity pause timeout for HistoryRecord{4054b008 player.org/.Player}
08-07 08:24:03.167: INFO/ActivityManager(67): Displayed com.android.launcher/com.android.launcher2.Launcher: +37s552ms
08-07 08:24:13.233: WARN/ActivityManager(67): Activity destroy timeout for HistoryRecord{4054b008 player.org/.Player}