[英]Java android RuntimeException Unable to instantiate activity ComponentInfo
[英]Unable to instantiate activity ComponentInfo, android using java
UPDATE
像個白痴一樣,我沒有注意logCat。 問題出在我瀏覽的頁面上,而不是意圖本身,我在setContentView代碼有機會在onContentLoad()中運行之前聲明了一些代碼。
感謝您的所有幫助!
我知道以前曾問過這個問題,但是我關注了無數關於該主題的帖子。 但似乎找不到正確的答案。 我正在嘗試從MainActivity頁面導航至ViewFeeds頁面; 但它引發了以上錯誤。
有趣的是,我已經有了在頁面之間導航的代碼,並且可以正常工作。 但是,當我為另一個類復制此代碼時,它將引發以上錯誤。
MainActivity代碼(我正在瀏覽的代碼):
public void btnFeedsClick(View v)
{
Button button = (Button) findViewById(R.id.button3);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, ViewFeeds.class);
MainActivity.this.startActivity(intent);
}
});
}
ViewFeeds類(我正在導航的類):
package com.example.rssapplication;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import android.app.ActionBar;
import android.app.Activity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
public class ViewFeeds extends Activity{
//The array which holds all of the data...
ArrayList<String> items = new ArrayList<String>();
ListView lv = (ListView) findViewById(R.id.listView1);
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.viewfeeds);
ActionBar actionBar = getActionBar();
actionBar.hide();
items = new ArrayList<String>();
String ret = "";
try {
InputStream inputStream = openFileInput("Teams.txt");
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
String receiveString = "";
StringBuilder stringBuilder = new StringBuilder();
// Toast.makeText(MainActivity.this, receiveString, Toast.LENGTH_LONG).show();
try {
while ( (receiveString = bufferedReader.readLine()) != null ) {
items.add(receiveString);
stringBuilder.append(receiveString + "\r\n");
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
inputStream.close();
//ret holds each line of text from the file...
ret = stringBuilder.toString();
TextView txt = (TextView) findViewById(R.id.textView6);
txt.setText(ret);
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(
this,
android.R.layout.simple_list_item_1,
items);
lv.setAdapter(arrayAdapter);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
android Manifest(我在聲明引用的部分上方添加了注釋):
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.rssapplication"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="19" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"></uses-permission>
<uses-permission android:name="android.permission.READ_PHONE_STATE"></uses-permission>
<uses-permission android:name="android.permission.DOWNLOAD_WITHOUT_NOTIFICATION" />
<application
android:allowBackup="true"
android:icon="@drawable/sportsoccericon"
android:label="@string/app_name"
android:theme="@style/AppTheme"
android:screenOrientation="portrait"
>
<activity
android:name="com.example.rssapplication.MainActivity"
android:label="@string/app_name"
>
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name="com.example.rssapplication.SelectTeams" android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MainActivity" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<!-- This is where I am creating the intent to navigate from main, to viewfeeds -->
<activity android:name="com.example.rssapplication.ViewFeeds" android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MainActivity" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity android:name="com.example.rssapplication.ShowArticle" android:label="@string/app_name"
android:parentActivityName="com.example.rssapplication.MyAdapter"
>
<!-- <meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.example.rssapplication.MyAdapter" />-->
<!-- <intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter> -->
</activity>
</application>
</manifest>
這是他的日志:
08-07 16:27:02.512: E/AndroidRuntime(2321): FATAL EXCEPTION: main
08-07 16:27:02.512: E/AndroidRuntime(2321): Process: com.example.rssapplication, PID: 2321
08-07 16:27:02.512: E/AndroidRuntime(2321): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.rssapplication/com.example.rssapplication.ViewFeeds}: java.lang.NullPointerException
08-07 16:27:02.512: E/AndroidRuntime(2321): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2231)
08-07 16:27:02.512: E/AndroidRuntime(2321): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2363)
08-07 16:27:02.512: E/AndroidRuntime(2321): at android.app.ActivityThread.access$900(ActivityThread.java:161)
08-07 16:27:02.512: E/AndroidRuntime(2321): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1265)
08-07 16:27:02.512: E/AndroidRuntime(2321): at android.os.Handler.dispatchMessage(Handler.java:102)
08-07 16:27:02.512: E/AndroidRuntime(2321): at android.os.Looper.loop(Looper.java:157)
08-07 16:27:02.512: E/AndroidRuntime(2321): at android.app.ActivityThread.main(ActivityThread.java:5356)
08-07 16:27:02.512: E/AndroidRuntime(2321): at java.lang.reflect.Method.invokeNative(Native Method)
08-07 16:27:02.512: E/AndroidRuntime(2321): at java.lang.reflect.Method.invoke(Method.java:515)
08-07 16:27:02.512: E/AndroidRuntime(2321): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
08-07 16:27:02.512: E/AndroidRuntime(2321): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
08-07 16:27:02.512: E/AndroidRuntime(2321): at dalvik.system.NativeStart.main(Native Method)
08-07 16:27:02.512: E/AndroidRuntime(2321): Caused by: java.lang.NullPointerException
08-07 16:27:02.512: E/AndroidRuntime(2321): at android.app.Activity.findViewById(Activity.java:1965)
08-07 16:27:02.512: E/AndroidRuntime(2321): at com.example.rssapplication.ViewFeeds.<init>(ViewFeeds.java:20)
08-07 16:27:02.512: E/AndroidRuntime(2321): at java.lang.Class.newInstanceImpl(Native Method)
08-07 16:27:02.512: E/AndroidRuntime(2321): at java.lang.Class.newInstance(Class.java:1208)
08-07 16:27:02.512: E/AndroidRuntime(2321): at android.app.Instrumentation.newActivity(Instrumentation.java:1079)
08-07 16:27:02.512: E/AndroidRuntime(2321): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2222)
08-07 16:27:02.512: E/AndroidRuntime(2321): ... 11 more
任何幫助將不勝感激!
謝謝,
卡勒姆
問題是這樣的:
ListView lv = (ListView) findViewById(R.id.listView1);
您太早調用findViewById()
了! 您始終必須注意活動生命周期 ! 只有在使用setContentView()
設置布局后才能調用findViewById()
setContentView()
。
您應該在onCreate()
查找如下Views
:
public class ViewFeeds extends Activity {
private ArrayList<String> items = new ArrayList<String>();
private ListView lv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.viewfeeds);
lv = (ListView) findViewById(R.id.listView1);
...
}
...
}
第一個問題在setContentView(R.layout.ur_layout)
之后的onCreate(...)
內部聲明
ListView lv = (ListView) findViewById(R.id.listView1);
您應使用應用程序的android:minSdkVersion="8"
作為第二個問題
ActionBar actionBar = getSupportActionBar();
而不是Activity
您必須擴展appcompat v7 support library
ActionbarActivity的 ActionBarActivity
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