我正在尝试使用main来启动3个选项卡，并且每个选项卡都指向一个单独的java / xml文件。我成功地使用#deprecation为4.0平台创建了它，并且它在2.3.3中正常工作但是一段时间后它已停止工作。我已经完成调试，无法弄清问题是什么。任何帮助，将不胜感激。 附件是main.java / main.xml和日志。如果您还需要，请告诉我。
Main.java
import android.app.TabActivity;
import android.content.Intent;
import android.content.res.Resources;
import android.os.Bundle;
import android.widget.TabHost;
public class Main extends TabActivity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Resources res = getResources(); // Resource object to get Drawables
TabHost tabHost = getTabHost(); // The activity TabHost
TabHost.TabSpec spec; // Resusable TabSpec for each tab
Intent intent; // Reusable Intent for each tab
// Create an Intent to launch an Activity for the tab (to be reused)
intent = new Intent().setClass(this, Joke.class);
// Initialize a TabSpec for each tab and add it to the TabHost
spec = tabHost.newTabSpec("Joke")
.setIndicator("", res.getDrawable(R.drawable.ic_tab_joke))
.setContent(intent);
tabHost.addTab(spec);
// Do the same for the other tabs
intent = new Intent().setClass(this, Picture.class);
spec = tabHost.newTabSpec("Picture")
.setIndicator("", res.getDrawable(R.drawable.ic_tab_picture))
.setContent(intent);
tabHost.addTab(spec);
intent = new Intent().setClass(this, Video.class);
spec = tabHost.newTabSpec("Video")
.setIndicator("", res.getDrawable(R.drawable.ic_tab_video))
.setContent(intent);
tabHost.addTab(spec);
tabHost.setCurrentTab(1);
}
}
main.xml中
<?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:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:padding="0dp" >
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:tabStripEnabled="false" />
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="5dp" />
</LinearLayout>
</TabHost>
LOG
03-15 16:26:49.625: I/ActivityManager(61): Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.example.oftheday/.Main } from pid 132
03-15 16:26:49.805: I/ActivityManager(61): Start proc com.example.oftheday for activity com.example.oftheday/.Main: pid=345 uid=10035 gids={3003}
03-15 16:26:50.365: I/ARMAssembler(61): generated scanline__00000177:03515104_00001002_00000000 [ 87 ipp] (110 ins) at [0x444ea6f0:0x444ea8a8] in 423460 ns
03-15 16:26:50.964: D/AndroidRuntime(345): Shutting down VM
03-15 16:26:50.964: W/dalvikvm(345): threadid=1: thread exiting with uncaught exception (group=0x40015560)
03-15 16:26:50.984: E/AndroidRuntime(345): FATAL EXCEPTION: main
03-15 16:26:50.984: E/AndroidRuntime(345): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.oftheday/com.example.oftheday.Main}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.oftheday/com.example.oftheday.Joke}: java.lang.NullPointerException
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.os.Handler.dispatchMessage(Handler.java:99)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.os.Looper.loop(Looper.java:123)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.ActivityThread.main(ActivityThread.java:3683)
03-15 16:26:50.984: E/AndroidRuntime(345): at java.lang.reflect.Method.invokeNative(Native Method)
03-15 16:26:50.984: E/AndroidRuntime(345): at java.lang.reflect.Method.invoke(Method.java:507)
03-15 16:26:50.984: E/AndroidRuntime(345): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-15 16:26:50.984: E/AndroidRuntime(345): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-15 16:26:50.984: E/AndroidRuntime(345): at dalvik.system.NativeStart.main(Native Method)
03-15 16:26:50.984: E/AndroidRuntime(345): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.oftheday/com.example.oftheday.Joke}: java.lang.NullPointerException
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.ActivityThread.startActivityNow(ActivityThread.java:1487)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:654)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.widget.TabHost.setCurrentTab(TabHost.java:326)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.widget.TabHost.addTab(TabHost.java:216)
03-15 16:26:50.984: E/AndroidRuntime(345): at com.example.oftheday.Main.onCreate(Main.java:27)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
03-15 16:26:50.984: E/AndroidRuntime(345): ... 11 more
03-15 16:26:50.984: E/AndroidRuntime(345): Caused by: java.lang.NullPointerException
03-15 16:26:50.984: E/AndroidRuntime(345): at java.io.Reader.<init>(Reader.java:65)
03-15 16:26:50.984: E/AndroidRuntime(345): at java.io.InputStreamReader.<init>(InputStreamReader.java:122)
03-15 16:26:50.984: E/AndroidRuntime(345): at java.io.InputStreamReader.<init>(InputStreamReader.java:59)
03-15 16:26:50.984: E/AndroidRuntime(345): at com.example.oftheday.Joke.DownloadText(Joke.java:62)
03-15 16:26:50.984: E/AndroidRuntime(345): at com.example.oftheday.Joke.onCreate(Joke.java:19)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
03-15 16:26:50.984: E/AndroidRuntime(345): ... 20 more
03-15 16:26:50.994: W/ActivityManager(61): Force finishing activity com.example.oftheday/.Main
从我能理解的是它指向main.java的第27行但是该行是 tabHost.addTab（SPEC）;我看不出任何问题。
感谢帮助：D
编辑1 - Joke.java
package com.example.oftheday;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class Joke extends Activity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
String str = DownloadText("test.com/text.txt"); // line 19
TextView jokeview = new TextView(this);
jokeview.setText(str);
TextView textview = new TextView(this);
textview.setText("" + str);
setContentView(R.layout.joke);
}
private InputStream OpenHttpConnection(String urlString) throws IOException {
InputStream in = null;
int response = -1;
URL url = new URL(urlString);
URLConnection conn = url.openConnection();
if (!(conn instanceof HttpURLConnection))
throw new IOException("Not an HTTP connection");
try {
HttpURLConnection httpConn = (HttpURLConnection) conn;
httpConn.setAllowUserInteraction(false);
httpConn.setInstanceFollowRedirects(true);
httpConn.setRequestMethod("GET");
httpConn.connect();
response = httpConn.getResponseCode();
if (response == HttpURLConnection.HTTP_OK) {
in = httpConn.getInputStream();
}
} catch (Exception ex) {
throw new IOException("Error connecting");
}
return in;
}
private String DownloadText(String URL) {
int BUFFER_SIZE = 2000;
InputStream in = null;
try {
in = OpenHttpConnection(URL);
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
return "";
}
InputStreamReader isr = new InputStreamReader(in); // line 62
int charRead;
String str = "";
char[] inputBuffer = new char[BUFFER_SIZE];
try {
while ((charRead = isr.read(inputBuffer)) > 0) {
// ---convert the chars to a String---
String readString = String
.copyValueOf(inputBuffer, 0, charRead);
str += readString;
inputBuffer = new char[BUFFER_SIZE];
}
in.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
return "";
}
return str;
}
}
Joke.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/jotd"
android:gravity="center"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center" />
</LinearLayout>
答案 0 :(得分：0)
异常一直级联到main.java，但异常的原因在堆栈跟踪中较低：
03-15 16:26:50.984: E/AndroidRuntime(345): Caused by: java.lang.NullPointerException
03-15 16:26:50.984: E/AndroidRuntime(345): at java.io.Reader.<init>(Reader.java:65)
03-15 16:26:50.984: E/AndroidRuntime(345): at java.io.InputStreamReader.<init>(InputStreamReader.java:122)
03-15 16:26:50.984: E/AndroidRuntime(345): at java.io.InputStreamReader.<init>(InputStreamReader.java:59)
03-15 16:26:50.984: E/AndroidRuntime(345): at com.example.oftheday.Joke.DownloadText(Joke.java:62)
03-15 16:26:50.984: E/AndroidRuntime(345): at com.example.oftheday.Joke.onCreate(Joke.java:19)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
03-15 16:26:50.984: E/AndroidRuntime(345): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
03-15 16:26:50.984: E/AndroidRuntime(345): ... 20 more
所以问题是在com.example.oftheday.Joke.DownloadText内你能发布该类的代码吗？您还可以在Eclipse上设置断点。了解如何操作here。
<强>更新
好的，首先看一下naming conventions。有些位难以阅读。
其次，我认为问题是你试图打开不存在的“test.com/text.txt”，因此，在OpenHttpConnection()内，条件response == HttpURLConnection.HTTP_OK永远不会成立，因此返回的InputStream保持为空（为您提供NullPointerException）
希望它有所帮助。