Android app unable to start activity componentinfo
I'm a new Android programmer and recently, a lot of my projects have been getting this error:
07-31 23:45:19.592: ERROR/AndroidRuntime(716): java.lang.RuntimeException: Unable to start
activity ComponentInfo{com.amrit.musifind/com.amrit.musifind.Main}:
java.lang.NullPointerException
Can anyone help me solve this problem?
Here's the entire logcat stack trace:
07-31 23:45:18.512: INFO/ActivityManager(63): Starting activity: Intent {
act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000
cmp=com.amrit.musifind/.Main }
07-31 23:45:18.682: INFO/ActivityManager(63): Start proc com.amrit.musifind for activity
com.amrit.musifind/.Main: pid=716 uid=10025 gids={3003}
07-31 23:45:18.962: INFO/jdwp(716): received file descriptor 20 from ADB
07-31 23:45:19.102: DEBUG/ddm-heap(716): Got feature list request
07-31 23:45:19.572: DEBUG/AndroidRuntime(716): Shutting down VM
07-31 23:45:19.572: WARN/dalvikvm(716): threadid=3: thread exiting with uncaught
exception (group=0x4001aa28)
07-31 23:45:19.572: ERROR/AndroidRuntime(716): Uncaught handler: thread main exiting due
to uncaught exception
07-31 23:45:19.592: ERROR/AndroidRuntime(716): java.lang.RuntimeException: Unable to
start activity ComponentInfo{com.amrit.musifind/com.amrit.musifind.Main}:
java.lang.NullPointerException
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2401)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2417)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
android.app.ActivityThread.access$2100(ActivityThread.java:116)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
android.os.Handler.dispatchMessage(Handler.java:99)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
android.os.Looper.loop(Looper.java:123)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
android.app.ActivityThread.main(ActivityThread.java:4203)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
java.lang.reflect.Method.invokeNative(Native Method)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
java.lang.reflect.Method.invoke(Method.java:521)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
dalvik.system.NativeStart.main(Native Method)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): Caused by: java.lang.NullPointerException
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
com.amrit.musifind.Main.onCreate(Main.java:44)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
07-31 23:45:19.592: ERROR/AndroidRuntime(716): ... 11 more
07-31 23:45:19.612: INFO/Process(63): Sending signal. PID: 716 SIG: 3
07-31 23:45:19.612: INFO/dalvikvm(716): threadid=7: reacting to signal 3
07-31 23:45:19.642: INFO/dalvikvm(716): Wrote stack trace to '/data/anr/traces.txt'
07-31 23:45:21.422: INFO/Process(716): Sending signal. PID: 716 SIG: 9
07-31 23:45:21.442: INFO/ActivityManager(63): Process com.amrit.musifind (pid 716) has
died.
07-31 23:45:21.583: WARN/UsageStats(63): Unexpected resume of com.android.launcher while
already resumed in com.amrit.musifind
07-31 23:45:21.712: WARN/InputManagerService(63): Window already focused, ignoring focus
gain of: com.android.internal.view.IInputMethodClient$Stub$Proxy@439559d0
07-31 23:45:23.482: DEBUG/AndroidRuntime(725): >>>>>>>>>>>>>> AndroidRuntime START
<<<<<<<<<<<<<<
07-31 23:45:23.482: DEBUG/AndroidRuntime(725): CheckJNI is ON
07-31 23:45:23.812: DEBUG/AndroidRuntime(725): --- registering native functions ---
07-31 23:45:23.832: INFO/jdwp(725): received file descriptor 20 from ADB
07-31 23:45:24.193: DEBUG/ddm-heap(725): Got feature list request
07-31 23:45:25.052: DEBUG/AndroidRuntime(725): Shutting down VM
07-31 23:45:25.052: DEBUG/dalvikvm(725): DestroyJavaVM waiting for non-daemon threads to
exit
07-31 23:45:25.062: DEBUG/dalvikvm(725): DestroyJavaVM shutting VM down
07-31 23:45:25.062: DEBUG/dalvikvm(725): HeapWorker thread shutting down
07-31 23:45:25.062: DEBUG/dalvikvm(725): HeapWorker thread has shut down
07-31 23:45:25.073: DEBUG/jdwp(725): JDWP shutting down net...
07-31 23:45:25.073: DEBUG/jdwp(725): +++ peer disconnected
07-31 23:45:25.073: INFO/dalvikvm(725): Debugger has detached; object registry had 1
entries
07-31 23:45:25.093: DEBUG/dalvikvm(725): VM cleaning up
07-31 23:45:25.113: DEBUG/dalvikvm(725): LinearAlloc 0x0 used 665652 of 4194304 (15%)
07-31 23:47:22.712: DEBUG/dalvikvm(104): GC freed 9173 objects / 524184 bytes in 149ms
Heres the 1st activity: start.java
package com.amrit.musifind;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import com.amrit.musifind.R;
import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public abstract class start extends Activity implements OnClickListener {
Button buttonGo, buttonReset;
EditText EditTextinput;
String input = "";
String ur = "http://www.tastekid.com/ask/ws?q=";
String l = "&f=musifin2125&k=mjjlnzkyzwuz&format=JSON";
String url = "" ;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
buttonGo = (Button) findViewById(R.id.buttonGo);
buttonReset = (Button) findViewById(R.id.buttonReset);
EditTextinput = (EditText) findViewById(R.id.EditTextinput);
//Button listener
buttonReset.setOnClickListener(this);
buttonGo.setOnClickListener(this);
}
public void onClick (View src){
switch(src.getId()){
case R.id.buttonGo:
input = EditTextinput.getText().toString();
url = ur + input + l ;
Intent Main = new Intent(this, ToClass.class);
Main.putExtra("userurl", url);
startActivity(Main);
break;
case R.id.buttonReset:
EditTextinput.setText("");
break;
}
}
}
The second activity: Main.java
package com.amrit.musifind;
import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import com.amrit.musifind.JSONfunctions;
import com.amrit.musifind.R;
import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.util开发者_JAVA百科.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class Main extends ListActivity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.listplaceholder);
Intent intent = getIntent();
String url = intent.getExtras().getString("userurl");
ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>
();
JSONObject json = JSONfunctions.getJSONfromURL(url);
try{
JSONObject earthquakes = json.getJSONObject("Similar");
JSONArray info = earthquakes.getJSONArray("Results");
for (int i = 0; i < info.length(); i++) {
HashMap<String, String> map = new HashMap<String, String>();
JSONObject e = info.getJSONObject(i);
map.put("id", String.valueOf(i));
map.put("name", "Name:" + e.getString("Name"));
map.put("type", "Type: " + e.getString("Type"));
mylist.add(map);
}
JSONArray results = json.getJSONArray("Results");
for(int i=0;i<results.length();i++){
HashMap<String, String> map = new HashMap<String, String>();
JSONObject e = results.getJSONObject(i);
map.put("id", String.valueOf(i));
map.put("name", "Name:" + e.getString("name"));
map.put("type", "Type: " + e.getString("type"));
mylist.add(map);
}
} catch(JSONException e) {
Log.e("log_tag", "Error parsing data "+e.toString());
}
ListAdapter adapter = new SimpleAdapter(this, mylist , R.layout.main,
new String[] { "name", "type" },
new int[] { R.id.item_title, R.id.item_subtitle });
setListAdapter(adapter);
final ListView lv = getListView();
lv.setTextFilterEnabled(true);
lv.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
@SuppressWarnings("unchecked")
HashMap<String, String> o = (HashMap<String, String>) lv.getItemAtPosition(position);
Toast.makeText(Main.this, "ID '" + o.get("id") + "' was clicked.",
Toast.LENGTH_SHORT).show();
}
});
}
}
Lastly, my manifest file: AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.amrit.musifind"
android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="4" />
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".start" android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.start" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name= ".Main">
<intent-filter>
<action android:name="android.intent.action.Main" />
</intent-filter>
</activity>
</application>
<uses-permission android:name="android.permission.INTERNET" />
</manifest>
Any help is much appreciated, without solving this problem I can't test my app out!
Your null pointer exception seems to be on this line:
String url = intent.getExtras().getString("userurl");
because intent.getExtras() returns null when the intent doesn't have any extras.
You have to realize that this piece of code:
Intent Main = new Intent(this, ToClass.class);
Main.putExtra("userurl", url);
startActivity(Main);
doesn't start the activity you wrote in Main.java, it will attempt to start an activity called ToClass and if that doesn't exist, your app crashes.
Also, there is no such thing as "android.intent.action.start" so the manifest should look more like:
<activity android:name=".start" 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= ".Main">
</activity>
I hope this fixes some of the issues you are encountering but I strongly suggest you check out some "getting started" tutorials for android development and build up from there.
The question is answered already, but I want add more information about the causes.
Android app unable to start activity componentinfo
This error often comes with appropriate logs. You can read logs and can solve this issue easily.
Here is a sample log. In which you can see clearly ClassCastException. So this issue came because TextView cannot be cast to EditText.
Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.EditText
11-04 01:24:10.403: D/AndroidRuntime(1050): Shutting down VM
11-04 01:24:10.403: W/dalvikvm(1050): threadid=1: thread exiting with uncaught exception (group=0x41465700)
11-04 01:24:10.543: E/AndroidRuntime(1050): FATAL EXCEPTION: main
11-04 01:24:10.543: E/AndroidRuntime(1050): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.troysantry.tipcalculator/com.troysantry.tipcalculator.TipCalc}: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.EditText
11-04 01:24:10.543: E/AndroidRuntime(1050): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
11-04 01:24:10.543: E/AndroidRuntime(1050): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
11-04 01:24:10.543: E/AndroidRuntime(1050): at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-04 01:24:10.543: E/AndroidRuntime(1050): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
11-04 01:24:10.543: E/AndroidRuntime(1050): at android.os.Handler.dispatchMessage(Handler.java:99)
11-04 01:24:10.543: E/AndroidRuntime(1050): at android.os.Looper.loop(Looper.java:137)
11-04 01:24:10.543: E/AndroidRuntime(1050): at android.app.ActivityThread.main(ActivityThread.java:5103)
11-04 01:24:10.543: E/AndroidRuntime(1050): at java.lang.reflect.Method.invokeNative(Native Method)
11-04 01:24:10.543: E/AndroidRuntime(1050): at java.lang.reflect.Method.invoke(Method.java:525)
11-04 01:24:10.543: E/AndroidRuntime(1050): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
11-04 01:24:10.543: E/AndroidRuntime(1050): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-04 01:24:10.543: E/AndroidRuntime(1050): at dalvik.system.NativeStart.main(Native Method)
11-04 01:24:10.543: E/AndroidRuntime(1050): Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.EditText
11-04 01:24:10.543: E/AndroidRuntime(1050): at com.troysantry.tipcalculator.TipCalc.onCreate(TipCalc.java:45)
11-04 01:24:10.543: E/AndroidRuntime(1050): at android.app.Activity.performCreate(Activity.java:5133)
11-04 01:24:10.543: E/AndroidRuntime(1050): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-04 01:24:10.543: E/AndroidRuntime(1050): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
11-04 01:24:10.543: E/AndroidRuntime(1050): ... 11 more
11-04 01:29:11.177: I/Process(1050): Sending signal. PID: 1050 SIG: 9
11-04 01:31:32.080: D/AndroidRuntime(1109): Shutting down VM
11-04 01:31:32.080: W/dalvikvm(1109): threadid=1: thread exiting with uncaught exception (group=0x41465700)
11-04 01:31:32.194: E/AndroidRuntime(1109): FATAL EXCEPTION: main
11-04 01:31:32.194: E/AndroidRuntime(1109): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.troysantry.tipcalculator/com.troysantry.tipcalculator.TipCalc}: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.EditText
11-04 01:31:32.194: E/AndroidRuntime(1109): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
11-04 01:31:32.194: E/AndroidRuntime(1109): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
11-04 01:31:32.194: E/AndroidRuntime(1109): at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-04 01:31:32.194: E/AndroidRuntime(1109): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
11-04 01:31:32.194: E/AndroidRuntime(1109): at android.os.Handler.dispatchMessage(Handler.java:99)
11-04 01:31:32.194: E/AndroidRuntime(1109): at android.os.Looper.loop(Looper.java:137)
11-04 01:31:32.194: E/AndroidRuntime(1109): at android.app.ActivityThread.main(ActivityThread.java:5103)
11-04 01:31:32.194: E/AndroidRuntime(1109): at java.lang.reflect.Method.invokeNative(Native Method)
11-04 01:31:32.194: E/AndroidRuntime(1109): at java.lang.reflect.Method.invoke(Method.java:525)
11-04 01:31:32.194: E/AndroidRuntime(1109): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
11-04 01:31:32.194: E/AndroidRuntime(1109): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-04 01:31:32.194: E/AndroidRuntime(1109): at dalvik.system.NativeStart.main(Native Method)
11-04 01:31:32.194: E/AndroidRuntime(1109): Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.EditText
11-04 01:31:32.194: E/AndroidRuntime(1109): at com.troysantry.tipcalculator.TipCalc.onCreate(TipCalc.java:44)
11-04 01:31:32.194: E/AndroidRuntime(1109): at android.app.Activity.performCreate(Activity.java:5133)
11-04 01:31:32.194: E/AndroidRuntime(1109): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-04 01:31:32.194: E/AndroidRuntime(1109): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
11-04 01:31:32.194: E/AndroidRuntime(1109): ... 11 more
11-04 01:36:33.195: I/Process(1109): Sending signal. PID: 1109 SIG: 9
11-04 02:11:09.684: D/AndroidRuntime(1167): Shutting down VM
11-04 02:11:09.684: W/dalvikvm(1167): threadid=1: thread exiting with uncaught exception (group=0x41465700)
11-04 02:11:09.855: E/AndroidRuntime(1167): FATAL EXCEPTION: main
11-04 02:11:09.855: E/AndroidRuntime(1167): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.troysantry.tipcalculator/com.troysantry.tipcalculator.TipCalc}: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.EditText
11-04 02:11:09.855: E/AndroidRuntime(1167): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
11-04 02:11:09.855: E/AndroidRuntime(1167): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
11-04 02:11:09.855: E/AndroidRuntime(1167): at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-04 02:11:09.855: E/AndroidRuntime(1167): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
11-04 02:11:09.855: E/AndroidRuntime(1167): at android.os.Handler.dispatchMessage(Handler.java:99)
11-04 02:11:09.855: E/AndroidRuntime(1167): at android.os.Looper.loop(Looper.java:137)
11-04 02:11:09.855: E/AndroidRuntime(1167): at android.app.ActivityThread.main(ActivityThread.java:5103)
11-04 02:11:09.855: E/AndroidRuntime(1167): at java.lang.reflect.Method.invokeNative(Native Method)
11-04 02:11:09.855: E/AndroidRuntime(1167): at java.lang.reflect.Method.invoke(Method.java:525)
11-04 02:11:09.855: E/AndroidRuntime(1167): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
11-04 02:11:09.855: E/AndroidRuntime(1167): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-04 02:11:09.855: E/AndroidRuntime(1167): at dalvik.system.NativeStart.main(Native Method)
11-04 02:11:09.855: E/AndroidRuntime(1167): Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.EditText
11-04 02:11:09.855: E/AndroidRuntime(1167): at com.troysantry.tipcalculator.TipCalc.onCreate(TipCalc.java:44)
11-04 02:11:09.855: E/AndroidRuntime(1167): at android.app.Activity.performCreate(Activity.java:5133)
11-04 02:11:09.855: E/AndroidRuntime(1167): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-04 02:11:09.855: E/AndroidRuntime(1167): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
11-04 02:11:09.855: E/AndroidRuntime(1167): ... 11 more
Some Common Mistakes.
1.findViewById() of non existing view
Like when you use findViewById(R.id.button) when button id does not exist in layout XML.
2. Wrong cast.
If you wrong cast some class, then you get this error. Like you cast RelativeLayout to LinearLayout or EditText to TextView.
3. Activity not registered in manifest.xml
If you did not register Activity in manifest.xml then this error comes.
4. findViewById() with declaration at top level
Below code is incorrect. This will create error. Because you should do findViewById() after calling setContentView(). Because an View can be there after it is created.
public class MainActivity extends Activity {
ImageView mainImage = (ImageView) findViewById(R.id.imageViewMain); //incorrect way
@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mainImage = (ImageView) findViewById(R.id.imageViewMain); //correct way
//...
}
}
5. Starting abstract Activity class.
When you try to start an Activity which is abstract, you will will get this error. So just remove abstract keyword before activity class name.
6. Using kotlin but kotlin not configured.
If your activity is written in Kotlin and you have not setup kotlin in your app. then you will get error. You can follow simple steps as written in Android Link or Kotlin Link. You can check this answer too.
More information
Read about Downcast and Upcast
Read about findViewById() method of Activity class
Super keyword in Java
How to register activity in manifest
加载中,请稍侯......
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