CODEWITHSUNDEEP
javaandroidandroid-intent
user3203324
user3203324

Reputation: 31

App cannot pass values between activities

I am working on an app in which the user inputs a number into one activity, and the number shows up on the next activity. This is what I have so far.

First activity: EnterText.java

public class EnterText extends Activity {

    //This is the string that will be passed to the next activity
    public static String mynumber = "com.example.ListviewExplorer.MESSAGE";

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.enter_text, menu);
        return true;
    }

    //This is where onClick, the button will invoke sendMessage
    //sendMessage is supposed to start the next activity
    public void sendMessage(View view){
        Intent intent = new Intent (this, DisplayText.class);
        EditText editText = (EditText) findViewById(R.id.editText1);
        mynumber = editText.getText().toString();
        intent.putExtra("MyNumber",mynumber);
        startActivity(intent);
    }

}

Second activity: DisplayText.java

public class DisplayText extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Bundle extras=getIntent().getExtras();
        String mynumber = extras.getString("MyNumber");
        TextView textview = (TextView)findViewById(R.id.textView1);
            textview.setText(EnterText.mynumber);

        setContentView(R.layout.activity_display_text);
        // Show the Up button in the action bar.
        setupActionBar();
    }
}

The problem is that this app crashes when I press the button on the first activity and it calls sendMessage; the second activity isn't even displayed.

Does anyone know why this is occurring?

LogCat is posted below.

Get to it!

05-29 11:57:59.385: W/dalvikvm(3046): threadid=1: thread exiting with uncaught exception (group=0x42d5d140)
05-29 11:57:59.425: E/AndroidRuntime(3046): FATAL EXCEPTION: main
05-29 11:57:59.425: E/AndroidRuntime(3046): Process: com.example.listviewexplorer, PID: 3046
05-29 11:57:59.425: E/AndroidRuntime(3046): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.listviewexplorer/com.example.listviewexplorer.DisplayText}: java.lang.NullPointerException
05-29 11:57:59.425: E/AndroidRuntime(3046):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at android.os.Handler.dispatchMessage(Handler.java:102)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at android.os.Looper.loop(Looper.java:136)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at android.app.ActivityThread.main(ActivityThread.java:5017)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at java.lang.reflect.Method.invokeNative(Native Method)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at java.lang.reflect.Method.invoke(Method.java:515)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at dalvik.system.NativeStart.main(Native Method)
05-29 11:57:59.425: E/AndroidRuntime(3046): Caused by: java.lang.NullPointerException
05-29 11:57:59.425: E/AndroidRuntime(3046):     at com.example.listviewexplorer.DisplayText.onCreate(DisplayText.java:21)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at android.app.Activity.performCreate(Activity.java:5231)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-29 11:57:59.425: E/AndroidRuntime(3046):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
05-29 11:57:59.425: E/AndroidRuntime(3046):     ... 11 more

Upvotes: 1

Views: 54

Answers (2)

indivisible
indivisible

Reputation: 5012

You need to assign the layout before using it.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // assign layout
    setContentView(R.layout.activity_display_text);
    // then you can use it
    TextView textview = (TextView)findViewById(R.id.textView1);
    textview.setText(EnterText.mynumber);
    ...
}

Since the layout has not been defined it is at that stage null and when you try to access Views inside it you get that NullPointerException thrown.

Upvotes: 3

laalto
laalto

Reputation: 152797

TextView textview = (TextView)findViewById(R.id.textView1);
textview.setText(EnterText.mynumber);

setContentView(R.layout.activity_display_text);

Before setContentView() findViewById() will return null no matter what, and invoking a method on null reference causes the NPE as seen in your stacktrace.

Move the setContentView() above the findViewById(), assuming that textView1 is actually in activity_display_text layout.

This fixes the NPE crash. To actually pass a value, have a look at some of the other answers.

Upvotes: 2

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