Android-启动新活动时出现空指针异常错误

Question

The following code accepts an intent from a listview that contains a listview. This activity captures the title of the listview selected, and then launches this activity, passing a string intent of the title. Before this activity loads, it crashes and logcat reports a 'Null Pointer Exception'. The items in the string array are as follows:

[0][.] = Id, starting at 0
[1][.] = name, the name as shown on the listview
[2][.] = description

ect

This is the view activity

 public class view extends HomeActivity {

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

        Bundle b = getIntent().getExtras();
        String value = b.getString("index");


        TextView title = (TextView) findViewById(R.id.textView1);
        TextView description = (TextView) findViewById(R.id.textView2);
        ImageView iv = (ImageView) findViewById(R.id.imageView1);
        RatingBar rb = (RatingBar) findViewById(R.id.ratingBar1);

        int tempPosition = 0;
        int intvalue = 0;

        //Find the id of the item[0], given the name[1]
        while(value!=Challenges.chalarray[tempPosition][1]){
            if (Challenges.chalarray[tempPosition][1].contains(value)){
                String s = Challenges.chalarray[tempPosition][0];
                intvalue = Integer.parseInt(s);
            }
            tempPosition = tempPosition + 1;
        }


        title.setText(Challenges.chalarray[intvalue][1]);
        description.setText(Challenges.chalarray[intvalue][2]);
        String temp = Challenges.chalarray[intvalue][4];
        String s1 = Challenges.chalarray[intvalue][3];
        float f1 = Float.parseFloat(s1);
        int resourceId = getResources().getIdentifier (temp, "drawable", "com.tim.listviewapp");
        iv.setImageResource(resourceId);
        rb.setRating(f1);

I'm 99% sure the sending side is correct, so I have not posted it. I am happy to post it if you guys think theres something wrong with it. Thank you HEAPS!

EDIT: Logcat:

    01-02 03:18:48.789: D/AndroidRuntime(1194): Shutting down VM
01-02 03:18:48.789: W/dalvikvm(1194): threadid=1: thread exiting with uncaught exception (group=0xb4b00b90)
01-02 03:18:48.849: E/AndroidRuntime(1194): FATAL EXCEPTION: main
01-02 03:18:48.849: E/AndroidRuntime(1194): Process: com.tim.listviewapp, PID: 1194
01-02 03:18:48.849: E/AndroidRuntime(1194): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.tim.listviewapp/com.tim.listviewapp.View}: java.lang.NullPointerException
01-02 03:18:48.849: E/AndroidRuntime(1194):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at android.app.ActivityThread.access$700(ActivityThread.java:135)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at android.os.Handler.dispatchMessage(Handler.java:102)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at android.os.Looper.loop(Looper.java:137)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at android.app.ActivityThread.main(ActivityThread.java:4998)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at java.lang.reflect.Method.invokeNative(Native Method)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at java.lang.reflect.Method.invoke(Method.java:515)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at dalvik.system.NativeStart.main(Native Method)
01-02 03:18:48.849: E/AndroidRuntime(1194): Caused by: java.lang.NullPointerException
01-02 03:18:48.849: E/AndroidRuntime(1194):     at com.tim.listviewapp.View.onCreate(View.java:35)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at android.app.Activity.performCreate(Activity.java:5243)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-02 03:18:48.849: E/AndroidRuntime(1194):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
01-02 03:18:48.849: E/AndroidRuntime(1194):     ... 11 more

EDIT AGAIN: (For Babibu)

01-02 03:51:15.760: W/dalvikvm(883): threadid=1: thread exiting with uncaught exception (group=0xb4a1db90)
01-02 03:51:15.820: E/AndroidRuntime(883): FATAL EXCEPTION: main
01-02 03:51:15.820: E/AndroidRuntime(883): Process: com.tim.listviewapp, PID: 883
01-02 03:51:15.820: E/AndroidRuntime(883): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.tim.listviewapp/com.tim.listviewapp.View}: java.lang.NullPointerException
01-02 03:51:15.820: E/AndroidRuntime(883):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
01-02 03:51:15.820: E/AndroidRuntime(883):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
01-02 03:51:15.820: E/AndroidRuntime(883):  at android.app.ActivityThread.access$700(ActivityThread.java:135)
01-02 03:51:15.820: E/AndroidRuntime(883):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
01-02 03:51:15.820: E/AndroidRuntime(883):  at android.os.Handler.dispatchMessage(Handler.java:102)
01-02 03:51:15.820: E/AndroidRuntime(883):  at android.os.Looper.loop(Looper.java:137)
01-02 03:51:15.820: E/AndroidRuntime(883):  at android.app.ActivityThread.main(ActivityThread.java:4998)
01-02 03:51:15.820: E/AndroidRuntime(883):  at java.lang.reflect.Method.invokeNative(Native Method)
01-02 03:51:15.820: E/AndroidRuntime(883):  at java.lang.reflect.Method.invoke(Method.java:515)
01-02 03:51:15.820: E/AndroidRuntime(883):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
01-02 03:51:15.820: E/AndroidRuntime(883):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
01-02 03:51:15.820: E/AndroidRuntime(883):  at dalvik.system.NativeStart.main(Native Method)
01-02 03:51:15.820: E/AndroidRuntime(883): Caused by: java.lang.NullPointerException
01-02 03:51:15.820: E/AndroidRuntime(883):  at com.tim.listviewapp.View.onCreate(View.java:44)
01-02 03:51:15.820: E/AndroidRuntime(883):  at android.app.Activity.performCreate(Activity.java:5243)
01-02 03:51:15.820: E/AndroidRuntime(883):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-02 03:51:15.820: E/AndroidRuntime(883):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
01-02 03:51:15.820: E/AndroidRuntime(883):  ... 11 more
01-02 03:51:19.270: I/Process(883): Sending signal. PID: 883 SIG: 9

Answer 1

您忘记初始化，请检查您的代码

Answer 2

Unfortanatly the log cat is not helping us.

Try running this code:

public class view extends Activity {

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

        Bundle b = getIntent().getExtras();
        String value = b.getString("index");


        TextView title = (TextView) findViewById(R.id.textView1);
        TextView description = (TextView) findViewById(R.id.textView2);
        ImageView iv = (ImageView) findViewById(R.id.imageView1);
        RatingBar rb = (RatingBar) findViewById(R.id.ratingBar1);

        isNull(title);
        isNull(description);
        isNull(iv);
        isNull(rb);

        int tempPosition = 0;
        int intvalue = 0;

        isNull(Challenges.chalarray);
        isNull(Challenges.chalarray[0]);
        isNull(Challenges.chalarray[1]);

        //Find the id of the item[0], given the name[1]
        while(value!=Challenges.chalarray[tempPosition][1]){
            if (Challenges.chalarray[tempPosition][1].contains(value)){
                String s = Challenges.chalarray[tempPosition][0];
                intvalue = Integer.parseInt(s);
            }
            tempPosition = tempPosition + 1;
        }

        isNull(Challenges.chalarray[0]);
        isNull(Challenges.chalarray[1]);
        isNull(Challenges.chalarray[2]);
        isNull(Challenges.chalarray[3]);
        isNull(Challenges.chalarray[4]);

        title.setText(Challenges.chalarray[intvalue][1]);
        description.setText(Challenges.chalarray[intvalue][2]);
        String temp = Challenges.chalarray[intvalue][4];
        String s1 = Challenges.chalarray[intvalue][3];
        float f1 = Float.parseFloat(s1);
        int resourceId = getResources().getIdentifier (temp, "drawable", "com.tim.listviewapp");
        iv.setImageResource(resourceId);
        rb.setRating(f1);
    }

    private void isNull(Object title) {
        if(title == null){
            Log.d("MyTag", "this is your error:");
            new Throwable("Exception log").printStackTrace();

        }

    }
}

I added a testNull method here to help us find the problem. How ever a much better solution would be if you could just debug it.

Answer 3

Your Challenges.chalarray is not initialised, so the first time you're trying to access it you get null. Change the initialisation to:

public class Challenges {
    public static String[][] chalarray = {
        { "0", "Challenge1", "Sample Description", "5", "base" },
        { "1", "Challenge2?", "Sample Description", "4", "base"},
        //etc
    };
}

Also, I'd change the while loop to run through all the elements in chalarray and to break from the loop when correct id is found:

while(tempPosition < Challenges.chalarray.length) {
    if (Challenges.chalarray[tempPosition][1].contains(value)) {
        String s = Challenges.chalarray[tempPosition][0];
        intvalue = Integer.parseInt(s);
        break;
    }
    tempPosition = tempPosition + 1;
}

Just keep in mind that if the id is not found, intvalue will be 0 from initialization, so in the following lines make sure you handle that, in other words, do you want to display the details of the element 0:

title.setText(Challenges.chalarray[intvalue][1]);
description.setText(Challenges.chalarray[intvalue][2]);
String temp = Challenges.chalarray[intvalue][4];
String s1 = Challenges.chalarray[intvalue][3];