Android错误：无法启动活动

Question

Here is the code I use to bring up the activity:

startActivity(new Intent(getApplicationContext(), Giveaway.class)); 

Here is the Activity that I am bringing up:

public class Giveaway extends Activity implements OnClickListener{

static SharedPreferences settings;
SharedPreferences.Editor prefEditor;

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

    settings = getSharedPreferences("firsttime", 0);

    LinearLayout facebook = (LinearLayout)findViewById(R.id.facebooklayout);
    Button later = (Button)findViewById(R.id.later);
    Button dontshowagain = (Button)findViewById(R.id.dontshowagain);

    facebook.setOnClickListener(this);
    later.setOnClickListener(this);
    dontshowagain.setOnClickListener(this);

}

public void onClick(View v) {
    switch (v.getId()) {
    case R.id.facebooklayout:
        Uri localuri = Uri.parse("http://www.facebook.com/pages/Bright-Design/366832480049386");
        startActivity(new Intent("android.intent.action.VIEW", localuri));
        break;
    case R.id.later:
        finish();
        break;
    case R.id.dontshowagain:
        finish();
        prefEditor = settings.edit();
        prefEditor.putBoolean("showgiveaway", false);
        prefEditor.commit();
        break;
    }
}

I have declared the Activity in my manifest folder:

<activity
        android:name=".Giveaway"
        android:label="@string/app_name"
        android:theme="@android:style/Theme.Dialog"
        android:screenOrientation="portrait"/>

But I keep getting a java.lang.RuntimeException: Unable to start activity java.lang.NullPointerException error. Here is my logcat:

    07-24 12:43:59.082: E/AndroidRuntime(7039): FATAL EXCEPTION: main
07-24 12:43:59.082: E/AndroidRuntime(7039): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.brightdesign.blackops2/com.brightdesign.blackops2.Giveaway}: java.lang.NullPointerException
07-24 12:43:59.082: E/AndroidRuntime(7039):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at android.os.Looper.loop(Looper.java:123)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at android.app.ActivityThread.main(ActivityThread.java:4627)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at java.lang.reflect.Method.invokeNative(Native Method)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at java.lang.reflect.Method.invoke(Method.java:521)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at dalvik.system.NativeStart.main(Native Method)
07-24 12:43:59.082: E/AndroidRuntime(7039): Caused by: java.lang.NullPointerException
07-24 12:43:59.082: E/AndroidRuntime(7039):     at com.brightdesign.blackops2.Giveaway.onCreate(Giveaway.java:29)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
07-24 12:43:59.082: E/AndroidRuntime(7039):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)

Answer 1

You need to post your layout code, but what is most likely happening is that one of these three lines is returning a null value:

LinearLayout facebook = (LinearLayout)findViewById(R.id.facebooklayout);
Button later = (Button)findViewById(R.id.later);
Button dontshowagain = (Button)findViewById(R.id.dontshowagain);

In the debugger step through those lines and if one is null, there is your problem because as soon as you try to set the on click listener it is going to fail.

Answer 2

Caused by: java.lang.NullPointerException
     at com.brightdesign.blackops2.Giveaway.onCreate(Giveaway.java:29)

Tells us that there is a NullPointerException in Giveaway.onCreate(), specifically Giveaway.java line 29. Odds are facebook , later , and/or dontshowagain is really null. Do you have all three of these defined in giveaway.xml?

Answer 3

Try this...

1.

Intent i = new Intent(Your_Activity.this, Another_Activity.class);
startActivity(i);

2. This below lines points to the class and the lines which are null.

Class: com.brightdesign.blackops2/com.brightdesign.blackops2.Giveaway}: java.lang.NullPointerException

Lines: Please check the below four lines, i think you are getting null value here.

Uri localuri = Uri.parse("http://www.facebook.com/pages/Bright-Design/366832480049386");



 LinearLayout facebook = (LinearLayout)findViewById(R.id.facebooklayout);
    Button later = (Button)findViewById(R.id.later);
    Button dontshowagain = (Button)findViewById(R.id.dontshowagain);