我得到空指针异常.这个错误似乎很常见，但我在网站上找到的所有答案都特定于其他代码中的问题，不幸的是我无法在我的代码中涉及.
Im getting null pointer exception. This error seems a pretty usual one, but all the answers I found on the site were specific to a problem in others code which unfortunately I cant relate to in my code.
我是 android 编程的新手.请帮助找出这个程序中的问题.这是代码.
I'm a novice to android programming. Please help figure out the problem in this program. Here's the code.
关于我想要做什么的一点点背景.我刚刚收到来自谷歌金融网络服务的 http 响应 &在 UI 中设置对 textView 组件的 http 响应
Little bit of background on what Im trying to do. I'm just getting the http response from the google finance web service & set the http response to the textView component in the UI
package com.android.myexchange;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
public class MyExchangeActivity extends Activity {
private Spinner spinner1, spinner2;
private Button btnSubmit;
private EditText textbox;
private TextView result;
private TextView test;
private static final String TAG = "MyApp";
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
spinner1 = (Spinner) findViewById(R.id.SpinnerA);
spinner2 = (Spinner) findViewById(R.id.SpinnerB);
btnSubmit = (Button) findViewById(R.id.btnSubmit);
textbox = (EditText) findViewById(R.id.textbox);
result = (TextView) findViewById(R.id.resulttext);
textbox.setText("Enter amount");
String testStr=HTTPRequestPoster.sendGetRequest("http://www.google.com/finance/converter", "a=1&from=USD&to=INR");
Log.i(TAG, "TEST");
result.setText(testStr);
addListenerOnButton();
}
private void addListenerOnButton() {
btnSubmit.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
Toast.makeText(MyExchangeActivity.this,
"OnClickListener : " +
"
Spinner 1 : "+ String.valueOf(spinner1.getSelectedItem()) +
"
Spinner 2 : "+ String.valueOf(spinner2.getSelectedItem()),
Toast.LENGTH_SHORT).show();
}
});
}
}
这是清单 xml:
<uses-sdk android:minSdkVersion="14" />
<uses-permission android:name="android.permission.INTERNET"/>
<application
android:icon="@drawable/ic_launcher"
android:label="@string/app_name" >
<activity
android:label="@string/app_name"
android:name=".MyExchangeActivity" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
这是日志:
12-19 21:47:42.403: W/System.err(647): android.os.NetworkOnMainThreadException
12-19 21:47:42.403: W/System.err(647): at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1084)
12-19 21:47:42.413: W/System.err(647): at java.net.InetAddress.lookupHostByName(InetAddress.java:391)
12-19 21:47:42.413: W/System.err(647): at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242)
12-19 21:47:42.413: W/System.err(647): at java.net.InetAddress.getAllByName(InetAddress.java:220)
12-19 21:47:42.413: W/System.err(647): at libcore.net.http.HttpConnection.<init>(HttpConnection.java:71)
12-19 21:47:42.413: W/System.err(647): at libcore.net.http.HttpConnection.<init>(HttpConnection.java:50)
12-19 21:47:42.423: W/System.err(647): at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:351)
12-19 21:47:42.423: W/System.err(647): at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:86)
12-19 21:47:42.423: W/System.err(647): at libcore.net.http.HttpConnection.connect(HttpConnection.java:128)
12-19 21:47:42.423: W/System.err(647): at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:308)
12-19 21:47:42.433: W/System.err(647): at libcore.net.http.HttpEngine.connect(HttpEngine.java:303)
12-19 21:47:42.433: W/System.err(647): at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:282)
12-19 21:47:42.433: W/System.err(647): at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:232)
12-19 21:47:42.433: W/System.err(647): at libcore.net.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:273)
12-19 21:47:42.433: W/System.err(647): at libcore.net.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:168)
12-19 21:47:42.433: W/System.err(647): at com.android.myexchange.HTTPRequestPoster.sendGetRequest(HTTPRequestPoster.java:43)
12-19 21:47:42.443: W/System.err(647): at com.android.myexchange.MyExchangeActivity.onCreate(MyExchangeActivity.java:37)
12-19 21:47:42.443: W/System.err(647): at android.app.Activity.performCreate(Activity.java:4465)
12-19 21:47:42.443: W/System.err(647): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
12-19 21:47:42.453: W/System.err(647): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
12-19 21:47:42.463: W/System.err(647): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
12-19 21:47:42.473: W/System.err(647): at android.app.ActivityThread.access$600(ActivityThread.java:122)
12-19 21:47:42.473: W/System.err(647): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
12-19 21:47:42.473: W/System.err(647): at android.os.Handler.dispatchMessage(Handler.java:99)
12-19 21:47:42.504: W/System.err(647): at android.os.Looper.loop(Looper.java:137)
12-19 21:47:42.504: W/System.err(647): at android.app.ActivityThread.main(ActivityThread.java:4340)
12-19 21:47:42.504: W/System.err(647): at java.lang.reflect.Method.invokeNative(Native Method)
12-19 21:47:42.513: W/System.err(647): at java.lang.reflect.Method.invoke(Method.java:511)
12-19 21:47:42.513: W/System.err(647): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
12-19 21:47:42.513: W/System.err(647): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
12-19 21:47:42.513: W/System.err(647): at dalvik.system.NativeStart.main(Native Method)
12-19 21:47:42.513: I/MyApp(647): TEST
12-19 21:47:42.523: D/AndroidRuntime(647): Shutting down VM
12-19 21:47:42.523: W/dalvikvm(647): threadid=1: thread exiting with uncaught exception (group=0x409951f8)
12-19 21:47:42.543: E/AndroidRuntime(647): FATAL EXCEPTION: main
12-19 21:47:42.543: E/AndroidRuntime(647): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.myexchange/com.android.myexchange.MyExchangeActivity}: java.lang.NullPointerException
12-19 21:47:42.543: E/AndroidRuntime(647): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
12-19 21:47:42.543: E/AndroidRuntime(647): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
12-19 21:47:42.543: E/AndroidRuntime(647): at android.app.ActivityThread.access$600(ActivityThread.java:122)
12-19 21:47:42.543: E/AndroidRuntime(647): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
12-19 21:47:42.543: E/AndroidRuntime(647): at android.os.Handler.dispatchMessage(Handler.java:99)
12-19 21:47:42.543: E/AndroidRuntime(647): at android.os.Looper.loop(Looper.java:137)
12-19 21:47:42.543: E/AndroidRuntime(647): at android.app.ActivityThread.main(ActivityThread.java:4340)
12-19 21:47:42.543: E/AndroidRuntime(647): at java.lang.reflect.Method.invokeNative(Native Method)
12-19 21:47:42.543: E/AndroidRuntime(647): at java.lang.reflect.Method.invoke(Method.java:511)
12-19 21:47:42.543: E/AndroidRuntime(647): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
12-19 21:47:42.543: E/AndroidRuntime(647): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
12-19 21:47:42.543: E/AndroidRuntime(647): at dalvik.system.NativeStart.main(Native Method)
12-19 21:47:42.543: E/AndroidRuntime(647): Caused by: java.lang.NullPointerException
12-19 21:47:42.543: E/AndroidRuntime(647): at com.android.myexchange.MyExchangeActivity.onCreate(MyExchangeActivity.java:39)
12-19 21:47:42.543: E/AndroidRuntime(647): at android.app.Activity.performCreate(Activity.java:4465)
12-19 21:47:42.543: E/AndroidRuntime(647): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
12-19 21:47:42.543: E/AndroidRuntime(647): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
12-19 21:47:42.543: E/AndroidRuntime(647): ... 11 more
这是布局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:background="@drawable/plain_white_paper"
android:orientation="vertical" >
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Spinner
android:id="@+id/SpinnerA"
android:layout_width="150dp"
android:layout_height="43dp"
android:layout_margin="10dp"
android:background="#8e99a4"
android:dropDownWidth="150dp"
android:entries="@array/currency"
android:textColor="@android:color/black" />
<EditText
android:id="@+id/textbox"
android:layout_width="135dp"
android:layout_height="38dp"
android:background="#8e99a4"
android:cursorVisible="true"
android:gravity="center_horizontal"
android:inputType="number"
android:text="@string/hello" >
<requestFocus />
</EditText>
</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Spinner
android:id="@+id/SpinnerB"
android:layout_width="150dp"
android:layout_height="50dp"
android:layout_margin="10dp"
android:background="#8e99a4"
android:dropDownWidth="150dp"
android:entries="@array/currency" />
<TextView
android:id="@+id/resulttext"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:layout_weight="0.68"
android:background="#8e99a4"
android:padding="25px"
android:text="@string/hello" />
</LinearLayout>
<Button
android:id="@+id/btnSubmit"
android:layout_width="128dp"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_margin="10dp"
android:text="Submit"
android:textColor="#181f25" />
<TextView
android:id="@+id/textView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="0.93"
android:text="TextView" />
</LinearLayout>
异常发生在我尝试将 http 响应文本 setText 到 TextView UI 组件的日志条目之后.据我所知，发生异常是因为 result.setText(testStr) 有一个我不明白的问题.HTTPRequestPost.java 类工作得很好.我已经测试过了它以字符串格式返回 httpresponse.如果您需要，我可以发布 HTTPRequestPost.java 的代码.
The exception occurs right after the log entry where I try to setText the http response text to TextView UI component. As far as I know the exception is occurring because result.setText(testStr) is having a porblem which I dont understand. The class HTTPRequestPost.java works perfectly fine. Ive tested it & it returns the httpresponse in string format. I can post code of HTTPRequestPost.java if you need it.
如您所述，HTTPRequestPoster.sendGetRequest() 返回 null.这是因为您需要 Internet 访问权限.将以下行添加到清单文件:
As you mentioned, The HTTPRequestPoster.sendGetRequest() returns null.
It is because you need Internet access permission. Add the below line to manifest file:
<uses-permission android:name="android.permission.INTERNET" />
您为 sendGetRequest() 提供的参数非常好.
只是您的 APK 需要获得访问 Internet 的权限.
The arguments you have given for sendGetRequest() are perfectly fine.
Its just that your APK needs permission to access Internet.
编辑:
在 StrictMode 中，它会阻止来自 UI 线程的网络访问.因此，您需要为网络活动创建一个单独的线程(或 AsyncTask).见以下代码:
EDIT :
In StrictMode, it blocks network access from UI thread. So you need to create a seperate thread (or AsyncTask) for network activity.
See code below:
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
.....
new Thread(new Runnable() {
@Override
public void run() {
String testStr=HTTPRequestPoster.sendGetRequest("http://www.google.com/finance/converter", "a=1&from=USD&to=INR");
Log.i(TAG, "TEST");
result.setText(testStr);
}
}).run();
/* String testStr=HTTPRequestPoster.sendGetRequest("http://www.google.com/finance/converter", "a=1&from=USD&to=INR");
Log.i(TAG, "TEST");
result.setText(testStr); */
addListenerOnButton();
}
这篇关于E/AndroidRuntime(3306): java.lang.RuntimeException: 无法启动活动 ComponentInfo{c的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持跟版网！