警报对话框不起作用，强制在启动时关闭

Question

My AlertDialog doesn't work, the app closes on launch.

Button btn_disclaimer = (Button) findViewById(R.id.btn_disclaimer);
    btn_disclaimer.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(MyActivity.this);
            alertDialogBuilder.setTitle("DISCLAIMER");
            alertDialogBuilder
                    .setMessage("TEST123")
                    .setNegativeButton("Okay", new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog, int id) {
                                    dialog.cancel();

                                }
                            });

            AlertDialog alertDialog = alertDialogBuilder.create();
            alertDialog.show();


        }
    });

What is wrong with it? I imported these guys:

import android.app.AlertDialog;
import android.content.DialogInterface;

I'm new to Android, just creating some simple apps.

java.lang.RuntimeException: Unable to start activity ComponentInfo{gd.mkp.jd.de.gymnasiumdamme/gd.mkp.jd.de.gymnasiumdamme.MyActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2216)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
            at android.app.ActivityThread.access$800(ActivityThread.java:145)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5140)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:611)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at gd.mkp.jd.de.gymnasiumdamme.MyActivity.onCreate(MyActivity.java:279)
            at android.app.Activity.performCreate(Activity.java:5231)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2170)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
            at android.app.ActivityThread.access$800(ActivityThread.java:145)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5140)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:611)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

To me it looks like your btn_disclaim object is null. Reasons:

1) You use the wrong id when doing the findViewById(R.id.btn_disclaimer). Make sure the button you're trying to reference actually has this id.

2) The button XML layout you are trying to reference is not actually in the XML layout you are loading with this Activity. The id exists, and so you can compile the app, but the view in which it exists is not the one you are loading using setContentView(R.layout.whatever_your_activity_layout_is). Make sure you are loading the correct layout, or make sure your button layout is actually defined in the layout you are load for this Activity.