嗨，我对Android dev很新，但是我搜索了这些论坛，没有发现任何结论。我试图使用ASyncTask在文本视图中显示来自站点的HTML。这是我在下面使用的代码。
package com.uad1001.theredux;
//imports
public class Htmlfromurl extends Activity {
Button btnSend;
EditText PhoneNo;
TextView t = new TextView(this);
String html;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_htmlfromurl);
t =(TextView)findViewById(R.id.IPDisplay);
// will implement later
//PhoneNo = (EditText) findViewById(R.id.phone);
//btnSend = (Button) findViewById(R.id.send);
String IPurl = "http://myexternalip.com/raw"; //URL I want to scrape
new event().execute(IPurl);
}
public class event extends AsyncTask<String, Void, String>{
@Override
protected String doInBackground(String...url) {
// TODO Auto-generated method stub
String urls = url[0];
try
{
Thread.sleep(4000);
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(urls);
ResponseHandler<String> resHandler = new BasicResponseHandler();
String page = httpClient.execute(httpGet, resHandler);
return page;
}
catch (ClientProtocolException e)
{
e.printStackTrace();
return "Error";
}
catch (IOException e)
{
e.printStackTrace();
return "Error";
}
catch (InterruptedException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
return "Error";
}
}
@Override
protected void onPostExecute(String page){
t.setText(page);
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.htmlfromurl, menu);
return true;
}
}
程序立即崩溃。 logcat显示： （也在http://pastebin.com/3sTENx2q）
08-05 19:38:54.082: W/dalvikvm(11472): threadid=1: thread exiting with uncaught exception (group=0x410942a0)
08-05 19:38:54.092: E/AndroidRuntime(11472): FATAL EXCEPTION: main
08-05 19:38:54.092: E/AndroidRuntime(11472): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.uad1001.theredux/com.uad1001.theredux.Htmlfromurl}: java.lang.NullPointerException
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2016)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2117)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.app.ActivityThread.access$700(ActivityThread.java:134)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1218)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.os.Handler.dispatchMessage(Handler.java:99)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.os.Looper.loop(Looper.java:137)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.app.ActivityThread.main(ActivityThread.java:4867)
08-05 19:38:54.092: E/AndroidRuntime(11472): at java.lang.reflect.Method.invokeNative(Native Method)
08-05 19:38:54.092: E/AndroidRuntime(11472): at java.lang.reflect.Method.invoke(Method.java:511)
08-05 19:38:54.092: E/AndroidRuntime(11472): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
08-05 19:38:54.092: E/AndroidRuntime(11472): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
08-05 19:38:54.092: E/AndroidRuntime(11472): at dalvik.system.NativeStart.main(Native Method)
08-05 19:38:54.092: E/AndroidRuntime(11472): Caused by: java.lang.NullPointerException
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.content.ContextWrapper.getResources(ContextWrapper.java:81)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.view.View.<init>(View.java:3296)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.view.View.<init>(View.java:3364)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.widget.TextView.<init>(TextView.java:584)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.widget.TextView.<init>(TextView.java:579)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.widget.TextView.<init>(TextView.java:575)
08-05 19:38:54.092: E/AndroidRuntime(11472): at com.uad1001.theredux.Htmlfromurl.<init>(Htmlfromurl.java:23)
08-05 19:38:54.092: E/AndroidRuntime(11472): at java.lang.Class.newInstanceImpl(Native Method)
08-05 19:38:54.092: E/AndroidRuntime(11472): at java.lang.Class.newInstance(Class.java:1319)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.app.Instrumentation.newActivity(Instrumentation.java:1068)
08-05 19:38:54.092: E/AndroidRuntime(11472): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2007)
08-05 19:38:54.092: E/AndroidRuntime(11472): ... 11 more
任何帮助都将不胜感激。
答案 0 :(得分：1)
我认为您的错误是由TextView t = new TextView(this);造成的。我不认为你想要像那样实例化它。相反，只需将其作为TextView t;保留在您的实例变量中，然后通过在onCreate方法中按ID查找它来实例化它。那应该可以解决问题。 TextView构造函数应该使用Context，它更像是一个抽象对象，因此使用构造函数实例化它通常是最好的。
答案 1 :(得分：1)
您可以使用droidQuery来处理大部分咕噜咕噜的工作：
public void includeHTML(TextView t, String url) {
$.ajax(new AjaxOptions().url("http://myexternalip.com/raw")
.type("get")
.dataType("html")
.context(this)
.success(new Function() {
@Override
public void invoke($ droidQuery, Object... params) {
$.with(t).html((String) params[0]);
}
})
.error(new Function() {
@Override
public void invoke($ droidQuery, Object... params) {
AjaxError error = (AjaxError) params[0];
Log.e("$", "Error " + error.status + ": " + error.error);
}
}));
}
然后你打电话：
includeHTML(t, url);
如果您想延迟4秒，可以使用：
$.setTimeout(new Function() {
@Override
public void invoke($ droidQuery, Object... params) {
runOnUiThread(new Runnable() {
includeHTML(t, url);
});
}
}, 4000);