CODEWITHSUNDEEP
androidandroid-layout
Martynas
Martynas

Reputation: 627

Buttons on other layout gives null exception

i have a question about layouts. When i try to describe buttons with onClickListener i get a Null exception. With buttons everything is ok, but they are on other layout, which is not created when this setup runs. Is this a problem and how to fix it?

    mMainViewButton = (Button) findViewById(R.id.btmainview);
    mMainViewButton.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {
            setContentView(R.layout.main);
        }
    });

    mKaireViewButton = (Button) findViewById(R.id.button_kaire);
    mKaireViewButton.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {
            setContentView(R.layout.test_page);
        }
    });

LogCat:

06-17 08:42:12.120: E/AndroidRuntime(2581): FATAL EXCEPTION: main
06-17 08:42:12.120: E/AndroidRuntime(2581): Process: com.example.android.BluetoothChat, PID: 2581
06-17 08:42:12.120: E/AndroidRuntime(2581): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.BluetoothChat/com.example.android.BluetoothChat.BluetoothChat}: java.lang.NullPointerException
06-17 08:42:12.120: E/AndroidRuntime(2581):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at android.app.ActivityThread.access$700(ActivityThread.java:135)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at android.os.Looper.loop(Looper.java:137)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at android.app.ActivityThread.main(ActivityThread.java:4998)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at java.lang.reflect.Method.invokeNative(Native Method)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at java.lang.reflect.Method.invoke(Method.java:515)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:811)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:627)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at dalvik.system.NativeStart.main(Native Method)
06-17 08:42:12.120: E/AndroidRuntime(2581): Caused by: java.lang.NullPointerException
06-17 08:42:12.120: E/AndroidRuntime(2581):     at com.example.android.BluetoothChat.BluetoothChat.setupChat(BluetoothChat.java:188)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at com.example.android.BluetoothChat.BluetoothChat.onStart(BluetoothChat.java:135)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at android.app.Activity.performStart(Activity.java:5253)
06-17 08:42:12.120: E/AndroidRuntime(2581):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2149)
06-17 08:42:12.120: E/AndroidRuntime(2581):     ... 11 more

Upvotes: 0

Views: 49

Answers (1)

Rod_Algonquin
Rod_Algonquin

Reputation: 26198

You cant use/reference a View that is located from another layout thus giving you NPE.

Also you need to have a layout before you reference a Button. setContentView(R.layout.main); must be declared before you call a Button reference.

setContentView(R.layout.layout_of_ur_buttons);
mMainViewButton = (Button) findViewById(R.id.btmainview);
mMainViewButton.setOnClickListener(new OnClickListener() {
    public void onClick(View v) {
        setContentView(R.layout.main);
    }
});

mKaireViewButton = (Button) findViewById(R.id.button_kaire);
mKaireViewButton.setOnClickListener(new OnClickListener() {
    public void onClick(View v) {
        setContentView(R.layout.test_page);
    }
});

As you could see that I specified the layout first before referencing a Button and that layout must contain your Buttons to avoid NPE.

Upvotes: 2

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