我在运行时不断收到此错误但没有编译错误？这是主要的 logcat 和代码。
05-25 12:29:25.543: W/dalvikvm(384): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
05-25 12:29:25.582: E/AndroidRuntime(384): FATAL EXCEPTION: main
05-25 12:29:25.582: E/AndroidRuntime(384): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.tablayout/com.example.tablayout.TablayoutActivity}: java.lang.NullPointerException
05-25 12:29:25.582: E/AndroidRuntime(384): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
05-25 12:29:25.582: E/AndroidRuntime(384): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
05-25 12:29:25.582: E/AndroidRuntime(384): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
05-25 12:29:25.582: E/AndroidRuntime(384): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
05-25 12:29:25.582: E/AndroidRuntime(384): at android.os.Handler.dispatchMessage(Handler.java:99)
05-25 12:29:25.582: E/AndroidRuntime(384): at android.os.Looper.loop(Looper.java:123)
05-25 12:29:25.582: E/AndroidRuntime(384): at android.app.ActivityThread.main(ActivityThread.java:4627)
05-25 12:29:25.582: E/AndroidRuntime(384): at java.lang.reflect.Method.invokeNative(Native Method)
05-25 12:29:25.582: E/AndroidRuntime(384): at java.lang.reflect.Method.invoke(Method.java:521)
05-25 12:29:25.582: E/AndroidRuntime(384): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
05-25 12:29:25.582: E/AndroidRuntime(384): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
05-25 12:29:25.582: E/AndroidRuntime(384): at dalvik.system.NativeStart.main(Native Method)
05-25 12:29:25.582: E/AndroidRuntime(384): Caused by: java.lang.NullPointerException
05-25 12:29:25.582: E/AndroidRuntime(384): at android.app.Activity.setContentView(Activity.java:1647)
05-25 12:29:25.582: E/AndroidRuntime(384): at android.app.TabActivity.ensureTabHost(TabActivity.java:114)
05-25 12:29:25.582: E/AndroidRuntime(384): at android.app.TabActivity.getTabHost(TabActivity.java:136)
05-25 12:29:25.582: E/AndroidRuntime(384): at com.example.tablayout.TablayoutActivity.<init>(TablayoutActivity.java:15)
05-25 12:29:25.582: E/AndroidRuntime(384): at java.lang.Class.newInstanceImpl(Native Method)
05-25 12:29:25.582: E/AndroidRuntime(384): at java.lang.Class.newInstance(Class.java:1429)
05-25 12:29:25.582: E/AndroidRuntime(384): at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
05-25 12:29:25.582: E/AndroidRuntime(384): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577)
05-25 12:29:25.582: E/AndroidRuntime(384): ... 11 more
<?xml version="1.0" encoding="utf-8"?>
<TabHost xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<LinearLayout android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:baselineAligned="false">
<FrameLayout android:layout_width="0dip"
android:layout_height="fill_parent"
android:layout_weight="0.2">
<TabWidget android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:visibility="invisible"/>
<LinearLayout android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">
<Button android:layout_height="0dip"
android:layout_width="fill_parent"
android:layout_weight="1.0"
android:background="@drawable/icon_photos_tab"
android:id="@+id/artist_id"
android:onClick="tabHandler"/>
<Button android:layout_height="0dip"
android:layout_width="fill_parent"
android:layout_weight="1.0"
android:background="@drawable/icon_videos_tab"
android:id="@+id/album_id"
android:onClick="tabHandler"/>
<Button android:layout_height="0dip"
android:layout_width="fill_parent"
android:layout_weight="1.0"
android:background="@drawable/icon_songs_tab"
android:id="@+id/song_id"
android:onClick="tabHandler"/>
</LinearLayout>
</FrameLayout>
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="0dip"
android:layout_height="fill_parent"
android:layout_weight="0.8"/>
</LinearLayout>
</TabHost>
这是 main.java 文件，这样您就可以看到它是如何成为全局变量以及我从哪里删除它的。还将按钮全局而不是本地添加到该位置。
import android.app.TabActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TabHost;
import android.widget.TabHost.TabSpec;
public class TablayoutActivity extends TabActivity {
/** Called when the activity is first created. */
Button artistButton, songButton, videosButton;
TabHost tabHost = getTabHost();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//TabHost tabHost = getTabHost();
// Tab for Photos
TabSpec photospec = tabHost.newTabSpec("Photos");
// setting Title and Icon for the Tab
photospec.setIndicator("Photos", getResources().getDrawable(R.drawable.icon_photos_tab));
Intent photosIntent = new Intent(this, PhotosActivity.class);
photospec.setContent(photosIntent);
// Tab for Songs
TabSpec songspec = tabHost.newTabSpec("Songs");
songspec.setIndicator("Songs", getResources().getDrawable(R.drawable.icon_songs_tab));
Intent songsIntent = new Intent(this, SongsActivity.class);
songspec.setContent(songsIntent);
// Tab for Videos
TabSpec videospec = tabHost.newTabSpec("Videos");
videospec.setIndicator("Videos", getResources().getDrawable(R.drawable.icon_videos_tab));
Intent videosIntent = new Intent(this, VideosActivity.class);
videospec.setContent(videosIntent);
// Adding all TabSpec to TabHost
tabHost.addTab(photospec); // Adding photos tab
tabHost.addTab(songspec); // Adding songs tab
tabHost.addTab(videospec); // Adding videos tab
}
public void tabHandler(View target){
artistButton.setSelected(false);
videosButton.setSelected(false);
songButton.setSelected(false);
if(target.getId() == R.id.artist_id){
tabHost.setCurrentTab(0);
artistButton.setSelected(true);
} else if(target.getId() == R.id.album_id){
tabHost.setCurrentTab(1);
videosButton.setSelected(true);
} else if(target.getId() == R.id.song_id){
tabHost.setCurrentTab(2);
songButton.setSelected(true);
}
};
}