我正在使用android工作室我曾尝试在单击按钮时创建AlertDialog但是当我尝试运行时，应用程序崩溃。请告诉我清楚的解决方案。
Ps：按钮位于卡片视图内。
主要java：
public class MainActivity extends AppCompatActivity {
private RecyclerView recyclerView;
private ItemAdapter itemAdapter;
private Button b1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
b1 = (Button) findViewById(R.id.button1);
b1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AlertDialog.Builder a_builder = new AlertDialog.Builder(MainActivity.this);
a_builder.setCancelable(false);
a_builder.setMessage("do you want to call!!!");
a_builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
Intent callIntent = new Intent(Intent.ACTION_CALL);
callIntent.setData(Uri.parse("tel:0000000000"));
if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CALL_PHONE) != PackageManager.PERMISSION_GRANTED) {
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return;
}
startActivity(callIntent);
}
});
a_builder.setNegativeButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
AlertDialog alert = a_builder.create();
alert.setTitle("Alert !");
alert.show();
}
});
final Toolbar toolbar = (Toolbar)findViewById(R.id.MyToolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
CollapsingToolbarLayout collapsingToolbarLayout = (CollapsingToolbarLayout)findViewById(R.id.collapse_toolbar);
collapsingToolbarLayout.setTitle("Service/DPNG");
ArrayList<Celebrity> itemList = new ArrayList<>();
fillDummyData(itemList);
recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
itemAdapter = new ItemAdapter(itemList);
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
recyclerView.setLayoutManager(mLayoutManager);
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.setAdapter(itemAdapter);
}
private void fillDummyData(ArrayList<Celebrity> celebList) {
Celebrity celeb1 = new Celebrity();
celeb1.setName("Johny.D");
celeb1.setFamousMovie("Pirates ");
celeb1.setProfilePhotoLocation("@drawable/contact1");
celebList.add(celeb1);
Celebrity celeb2 = new Celebrity();
celeb2.setName("Arnold");
celeb2.setFamousMovie("The Terminator");
celeb2.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTI3MDc4NzUyMV5BMl5BanBnXkFtZTcwMTQyMTc5MQ@@._V1._SY209_CR13,0,140,209_.jpg");
celebList.add(celeb2);
Celebrity celeb3 = new Celebrity();
celeb3.setName("Emma.W");
celeb3.setFamousMovie("Harry Potter ");
celeb3.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTQ3ODE2NTMxMV5BMl5BanBnXkFtZTgwOTIzOTQzMjE@._V1._SY209_CR14,0,140,209_.jpg");
celebList.add(celeb3);
Celebrity celeb4 = new Celebrity();
celeb4.setName("Daniel");
celeb4.setFamousMovie("Harry Potter ");
celeb4.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTg4NTExODc3Nl5BMl5BanBnXkFtZTgwODUyMDEzMDE@._V1._SY209_CR8,0,140,209_.jpg");
celebList.add(celeb4);
Celebrity celeb5 = new Celebrity();
celeb5.setName("Leonardo");
celeb5.setFamousMovie("Inception");
celeb5.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMjI0MTg3MzI0M15BMl5BanBnXkFtZTcwMzQyODU2Mw@@._V1._SY209_CR7,0,140,209_.jpg");
celebList.add(celeb5);
Celebrity celeb6 = new Celebrity();
celeb6.setName("TomCr");
celeb6.setFamousMovie("Top Gun");
celeb6.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTk1MjM3NTU5M15BMl5BanBnXkFtZTcwMTMyMjAyMg@@._V1._SY209_CR9,0,140,209_.jpg");
celebList.add(celeb6);
Celebrity celeb7 = new Celebrity();
celeb7.setName("Charles.C");
celeb7.setFamousMovie("Modern Times");
celeb7.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BNDcwMDc0ODAzOF5BMl5BanBnXkFtZTgwNTY2OTI1MDE@._V1._SX140_CR0,0,140,209_.jpg");
celebList.add(celeb7);
Celebrity celeb8 = new Celebrity();
celeb8.setName("Morgan.F");
celeb8.setFamousMovie("The Shawshank ");
celeb8.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTc0MDMyMzI2OF5BMl5BanBnXkFtZTcwMzM2OTk1MQ@@._V1._SX140_CR0,0,140,209_.jpg");
celebList.add(celeb8);
Celebrity celeb9 = new Celebrity();
celeb9.setName("Tom.Ha");
celeb9.setFamousMovie("The Da Vinci Code");
celeb9.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTQ2MjMwNDA3Nl5BMl5BanBnXkFtZTcwMTA2NDY3NQ@@._V1._SY209_CR2,0,140,209_.jpg");
celebList.add(celeb9);
Celebrity celeb10 = new Celebrity();
celeb10.setName("Hugh ");
celeb10.setFamousMovie("The Prestige");
celeb10.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BNDExMzIzNjk3Nl5BMl5BanBnXkFtZTcwOTE4NDU5OA@@._V1._SX140_CR0,0,140,209_.jpg");
celebList.add(celeb10);
Celebrity celeb11 = new Celebrity();
celeb11.setName("Matt ");
celeb11.setFamousMovie("The Bourne Identity");
celeb11.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTM0NzYzNDgxMl5BMl5BanBnXkFtZTcwMDg2MTMyMw@@._V1._SY209_CR8,0,140,209_.jpg");
celebList.add(celeb11);
Celebrity celeb12 = new Celebrity();
celeb12.setName("Sylvester ");
celeb12.setFamousMovie("Rocky");
celeb12.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTQwMTk3NDU2OV5BMl5BanBnXkFtZTcwNTA3MTI0Mw@@._V1._SY209_CR5,0,140,209_.jpg");
celebList.add(celeb12);
Celebrity celeb13 = new Celebrity();
celeb13.setName("Will ");
celeb13.setFamousMovie("Men in Black");
celeb13.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BNTczMzk1MjU1MV5BMl5BanBnXkFtZTcwNDk2MzAyMg@@._V1._SY209_CR2,0,140,209_.jpg");
celebList.add(celeb13);
Celebrity celeb14 = new Celebrity();
celeb14.setName("Steven ");
celeb14.setFamousMovie("Saving Private ");
celeb14.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTY1NjAzNzE1MV5BMl5BanBnXkFtZTYwNTk0ODc0._V1._SX140_CR0,0,140,209_.jpg");
celebList.add(celeb14);
Celebrity celeb15 = new Celebrity();
celeb15.setName("Al ");
celeb15.setFamousMovie("The Godfather");
celeb15.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTQzMzg1ODAyNl5BMl5BanBnXkFtZTYwMjAxODQ1._V1._SX140_CR0,0,140,209_.jpg");
celebList.add(celeb15);
Celebrity celeb16 = new Celebrity();
celeb16.setName("Robert");
celeb16.setFamousMovie("The Avengers");
celeb16.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BNzg1MTUyNDYxOF5BMl5BanBnXkFtZTgwNTQ4MTE2MjE@._V1._SX140_CR0,0,140,209_.jpg");
celebList.add(celeb16);
Celebrity celeb17 = new Celebrity();
celeb17.setName("Nat");
celeb17.setFamousMovie("V for Vendetta");
celeb17.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTQ3ODE3Mjg1NV5BMl5BanBnXkFtZTcwNzA4ODcxNA@@._V1._SY209_CR8,0,140,209_.jpg");
celebList.add(celeb17);
Celebrity celeb18 = new Celebrity();
celeb18.setName("Dwayne");
celeb18.setFamousMovie("WWE Raw");
celeb18.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTkyNDQ3NzAxM15BMl5BanBnXkFtZTgwODIwMTQ0NTE@._V1._SX140_CR0,0,140,209_.jpg");
celebList.add(celeb18);
Celebrity celeb19 = new Celebrity();
celeb19.setName("Jackie ");
celeb19.setFamousMovie("Jackie Chan ");
celeb19.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTk4MDM0MDUzM15BMl5BanBnXkFtZTcwOTI4MzU1Mw@@._V1._SY209_CR5,0,140,209_.jpg");
celebList.add(celeb19);
Celebrity celeb20 = new Celebrity();
celeb20.setName("Scarlet");
celeb20.setFamousMovie("Lost in ");
celeb20.setProfilePhotoLocation("http://ia.media-imdb.com/images/M/MV5BMTM3OTUwMDYwNl5BMl5BanBnXkFtZTcwNTUyNzc3Nw@@._V1._SY209_CR16,0,140,209_.jpg");
celebList.add(celeb20);
}
}
logcat：
09-14 21:18:04.476 26368-26368/com.example.apollo.bbpp E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.apollo.bbpp/com.example.apollo.bbpp.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2099)
at android.app.ActivityThread.access$600(ActivityThread.java:138)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4929)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:798)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:565)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.apollo.bbpp.MainActivity.onCreate(MainActivity.java:48)
at android.app.Activity.performCreate(Activity.java:5254)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1082)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2038)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2099)
at android.app.ActivityThread.access$600(ActivityThread.java:138)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4929)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:798)
答案 0 :(得分：0)
public void onClick(View v) {
AlertDialog.Builder a_builder = new AlertDialog.Builder(MainActivity.this);
a_builder.setCancelable(false);
a_builder.setTitle("Alert !");
a_builder.setMessage("do you want to call!!!");
a_builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
//handle the permission at start.
if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CALL_PHONE) != PackageManager.PERMISSION_GRANTED) {
//permission not granted, ask for permission
return;
}
Intent callIntent = new Intent(Intent.ACTION_CALL);
callIntent.setData(Uri.parse("tel:0000000000"));
startActivity(callIntent);
}
});
a_builder.setNegativeButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
AlertDialog alert = a_builder.create();
alert.show();
}
});