空指针异常android数组

Question

I am making an app that has 2 java classes: MainActivity and SecondActivity . MainActivity initiates the SecondActivity by using an onClick method.

The SecondActivity has 2 arrays stored in the strings.xml file. The SecondActivity class wants to store all the array variables from strings.xml to itself, in order to use it for some methods. I think i am doing it the wrong way, as i tried storing the arrays directly in the SecondActivity and it worked but when i am storing the arrays in strings.xml it gives a NullPointerException .

Here is the SecondActivity code:

package com.android.ict.seneca.androidpocketguide;

import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class SecondActivity extends Activity {

    private final String CLASS_NAME = "SecondActivity";

    String [] Vocabularies = getResources().getStringArray(R.array.Vocabularies_array);
    String [] meanings = getResources().getStringArray(R.array.meanings_array);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(
                this,
                android.R.layout.simple_dropdown_item_1line, Vocabularies);

        //ArrayAdapter<String> adapter2 = new ArrayAdapter<String>(this,android.R.layout.simple_dropdown_item_1line, meanings);

        AutoCompleteTextView textView =
                (AutoCompleteTextView) findViewById(R.id.vocabularies);

        textView.setThreshold(2); // minimum number of characters to be typed

        textView.setAdapter(adapter); // connect the list of suggestions to the View object

    }

    public void onStart(){
        super.onStart();
        Log.d( CLASS_NAME, "onStart invoked!" );
    }

    public void onPause(){
        super.onPause();
        Log.d( CLASS_NAME, "onPause invoked!!" );
    }

    public void onResume(){
        super.onResume();
        Log.d( CLASS_NAME, "onResume invoked!!" );
    }

    public void onStop(){
        super.onStop();
        Log.d( CLASS_NAME, "onStop invoked!!!" );
    }

    public void onDestroy(){
        super.onDestroy();
        Log.d( CLASS_NAME, "onDestroy INVOKED!!!" );
    }

    public void onRestart(){
        super.onRestart();
        Log.d( CLASS_NAME, "onRestart invoked!!" );
    }

    // event handler for the button
    public void onClick(View view) {


        Intent data = new Intent();

        EditText usr =
                (EditText) findViewById(R.id.vocabularies); // get user input

        // set the data part (an URI reference) of an intent
        data.setData(Uri.parse(usr.getText().toString()));
        String s = data.getData().toString();

        int flag = 0;

        for(int i=0; i<Vocabularies.length;i++)
        {
            if(s.equals(Vocabularies[i]))
            {
                flag = i;
            }
        }

        Toast.makeText(this, "YOU'VE ENTERED: " + s, Toast.LENGTH_LONG ).show();

        String m = meanings[flag];
        String disp = "Vocabulary: " + s + "\n" + "Meaning: " + m;

        TextView textViewObj1 = (TextView) findViewById(R.id.meaning);
        textViewObj1.setText(disp);

        //finish();   //--- close the activity AND RETURN CONTROL TO THE REQUESTING ACTIVITY


        //EditText txt_username = (EditText) findViewById(R.id.txt_username);
    } // end onClick
}

Here is the MainActivity code:

package com.android.ict.seneca.androidpocketguide;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private final String CLASS_NAME = "FirstActiviy";
    private int request_Code = 1;


    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d( CLASS_NAME, "onCreate invoked!" );
    }

    public void onStart(){
        super.onStart();
        Log.d( CLASS_NAME, "onStart invoked!" );
    }

    public void onPause(){
        super.onPause();
        Log.d( CLASS_NAME, "onPause invoked!!" );
    }

    public void onResume(){
        super.onResume();
        Log.d( CLASS_NAME, "onResume invoked!!" );
    }

    public void onStop(){
        super.onStop();
        Log.d( CLASS_NAME, "onStop invoked!!!" );
    }

    public void onDestroy(){
        super.onDestroy();
        Log.d( CLASS_NAME, "onDestroy INVOKED!!!" );
    }

    public void onRestart(){
        super.onRestart();
        Log.d( CLASS_NAME, "onRestart invoked!!" );
    }


    // event handler for the button (activity 2)
    public void onClick(View view) {

        startActivityForResult( new Intent(
                        "com.android.ict.seneca.androidpocketguide.second"), // declared  by an intent filter
                request_Code);   // (requesting) activity ID

        Log.d( CLASS_NAME, "after startActivityForResult" );
//intent.setData(Uri.parse("com.seneca.lab2b.abbas"));
        //startActivity(intent);
    }

    /*
    public void onActivityResult( int requestCode,   // used to match the REQUESTING activity ID
                                  int resultCode,    // result code set by the sender (i.e. the TARGET activity)
                                  Intent data )      // an intent passed by the sender (i.e. the TARGET activity)
    {
        if (requestCode == request_Code) {
            if (resultCode == RESULT_OK) {


                //TextToSpeech(data.getData().toString());

                Intent intent = getIntent();

                String s = data.getData().toString();

                TextView textViewObj1 = (TextView) findViewById(R.id.line);
                textViewObj1.setText(s);


                Toast.makeText(
                        this,
                        "MESSAGE RECEIVED: " + s,  // retrieve data from the intent
                        // API Question: What is the  return type of getData()?
                        Toast.LENGTH_LONG ).show();
            }
        }
        Log.d( CLASS_NAME, "onActivityResult: what is next?" );
    }


    // event handler for a button (activity 3)
    public void onClick3(View view) {

        Intent dataIntent = new Intent( this, ThirdActivity.class );//"com.seneca.lab2b.third"); // explicit intent

        // the putExtra( ) method
        dataIntent.putExtra( "greeting", "Good morning  Android!" );
        dataIntent.putExtra( "number", 123 );

        // create a Bundle object
        Bundle bundle = new Bundle();
        bundle.putString( "My name", "Abbas Zoeb" );
        bundle.putInt( "Student ID", 56789  );

        // putExtras( ): store the bundle in the intent
        dataIntent.putExtras( bundle );

        // launch the third activity
        startActivity( dataIntent );

        //startActivity( new Intent( this, ThirdActivity.class ) );

    }
    */

}

Here is the error log:

09-21 23:43:19.907 26183-26183/com.android.ict.seneca.androidpocketguide E/AndroidRuntime: FATAL EXCEPTION: main Process: com.android.ict.seneca.androidpocketguide, PID: 26183 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.android.ict.seneca.androidpocketguide/com.android.ict.seneca.androidpocketguide.SecondActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) at android.app.ActivityThread.-wrap11(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5417) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference at android.content.ContextWrapper.getResources(ContextWrapper.java:87) at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81) at com.android.ict.seneca.androidpocketguide.SecondActivity.(SecondActivity.java:22) at java.lang.Class.newInstance(Native Method) at android.app.Instrumentation.newActivity(Instrumentation.java:1067) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) at android.app.ActivityThread.-wrap11(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) at android.os.Handler.dispatchM essage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5417) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Here is the string.xml file:

<resources>
    <string name="app_name">Android Pocket Guide</string>
    <string-array name="Vocabularies_array">
        <item>activity</item>
        <item>AVD</item>
        <item>ART</item>
        <item>Dalvik</item>
        <item>intent</item>
        <item>intent filter</item>
        <item>explicit intent</item>
        <item>implicit intent</item>
        <item>LogCat</item>
        <item>bundle</item>
        <item>Gradle</item>
        <item>Android Device Monitor</item>
        <item>SDK manager</item>
        <item>minSdkVersion</item>
    </string-array>

    <string-array name="meanings_array">
        <item>An activity represents a single screen with a user interface just like window or frame of Java</item>
        <item>An Android Virtual Device (AVD) is an emulator configuration that lets you model an actual device by defining hardware and software options to be emulated by the Android Emulator.</item>
        <item>Android Runtime (ART) is an application runtime environment used by the Android operating system.</item>
        <item>Dalvik is a part of the software stack that makes up the Android platform.</item>
        <item>Intent can be defined as a simple message objects which is used to communicate from 1 activity to another.</item>
        <item>Specifies the types of intents that an activity, service, or broadcast receiver can respond to</item>
        <item>An explicit intent is one that you use to launch a specific app component, such as a particular activity or service in your app</item>
        <item>Implicit intents do not name a specific component, but instead declare a general action to perform, which allows a component from another app to handle it.</item>
        <item>Logcat is a command-line tool that dumps a log of system messages, including stack traces when the device throws an error and messages that you have written from your app with the Log class.</item>
        <item>A Bundle is a set of key/value pairs, where it implements an interface called Parcelable.</item>
        <item>Gradle is a custom build tool used to build android packages (apk files) by managing dependencies and providing custom build logic.</item>
        <item>Android Device Monitor is a standalone tool that provides a UI for several Android application debugging and analysis tools.</item>
        <item>A software development kit that enables developers to create applications for the Android platform.</item>
        <item>An integer designating the minimum API Level required for the application to run.</item>
    </string-array>


</resources>

Answer 1

Try this way

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        Vocabularies = getResources().getStringArray(R.array.Vocabularies_array);
        meanings = getResources().getStringArray(R.array.meanings_array);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(
                this,
                android.R.layout.simple_dropdown_item_1line, Vocabularies);

        //ArrayAdapter<String> adapter2 = new ArrayAdapter<String>(this,android.R.layout.simple_dropdown_item_1line, meanings);

        AutoCompleteTextView textView =
                (AutoCompleteTextView) findViewById(R.id.vocabularies);

        textView.setThreshold(2); // minimum number of characters to be typed

        textView.setAdapter(adapter); // connect the list of suggestions to the View object

    }

Answer 2

Try declaring your arrays in the global context, then assigning them some value during one of the activity's lifecycle stages (ie onCreate(), onResume(), etc.).

The issue you're having is with getResources() . I would create a global variable of type Context . Then, what I would do in onCreate() is this:

context = this;
vocabularies = context.getResources().getStringArray(R.array.Vocabularies_array);
meanings = context.getResources().getStringArray(R.array.meanings_array);

Hope that helps!

Answer 3

These variable initializations...

String [] Vocabularies = getResources().getStringArray(R.array.Vocabularies_array);
String [] meanings = getResources().getStringArray(R.array.meanings_array);

...probably need to go in a constructor, or even more likely in onCreate(...) , specifically after

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_second);

Answer 4

Initialization of the variables in some method like oncreate/onPostcreated eg

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Vocabularies = getResources().getStringArray(R.array.Vocabularies_array);
    meanings = getResources().getStringArray(R.array.meanings_array);

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(
            this,
            android.R.layout.simple_dropdown_item_1line, Vocabularies);

    //ArrayAdapter<String> adapter2 = new ArrayAdapter<String>(this,android.R.layout.simple_dropdown_item_1line, meanings);

    AutoCompleteTextView textView =
            (AutoCompleteTextView) findViewById(R.id.vocabularies);

    textView.setThreshold(2); // minimum number of characters to be typed

    textView.setAdapter(adapter); // connect the list of suggestions to the View object

}