我将遵循本教程来探索Firebase并使用三个java类
- 主活动
- RegisterActivity
- ProfileActivity
和三个布局视图。
- activity_main.xml
- activity_register.xml
- profilepage.xml
[Youtube教程]1我得到
java.lang.RuntimeException：无法启动活动ComponentInfo｛com.example.firebaselearning/com.example.fireaselearning.RegisterActivity｝：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法"void android.widget.Button.setOnClickListener(android.view.view$OnClickListen(">
完全错误
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.firebaselearning, PID: 8008
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.firebaselearning/com.example.firebaselearning.RegisterActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.firebaselearning.RegisterActivity.onCreate(RegisterActivity.java:60)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
以下是代码(不包括gradle，因为我不认为它是错误的来源(
MainActivity.java
public class MainActivity extends AppCompatActivity {
//views
Button mRegisterBtn, mLogInBtn;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//initialise view
mRegisterBtn = findViewById(R.id.registerbutton);
mLogInBtn = findViewById(R.id.login);
//handle register button click
mRegisterBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//start register activity
startActivity(new Intent(MainActivity.this, RegisterActivity.class));
}
});
}
}
RegisterActivity.java
public class RegisterActivity extends AppCompatActivity {
//views
EditText mEmailET, mPassword;
Button mRegistrationBTN;
//progressbar to display progress which registering
ProgressDialog progressDialog;
//declare instance of fireAuth
private FirebaseAuth mAuth;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_register);
//actionbar and its title
ActionBar actionBar = getSupportActionBar();
actionBar.setTitle("Create Account");
//enable back button
actionBar.setDisplayHomeAsUpEnabled(true);
actionBar.setDisplayShowHomeEnabled(true);
//init
mEmailET = findViewById(R.id.editTextTextEmailAddress);
mPassword = findViewById(R.id.editTextTextPassword);
mRegistrationBTN = findViewById(R.id.registerbutton);
//initialising firebaseAuth instance
mAuth = FirebaseAuth.getInstance();
progressDialog = new ProgressDialog(this);
progressDialog.setMessage("Registering user ...");
//handle register btn click
mRegistrationBTN.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//input email, password
String email = mEmailET.getText().toString().trim();
String password = mPassword.getText().toString().trim();
//validate
if(Patterns.EMAIL_ADDRESS.matcher(email).matches()){
//show error and focus to edittext
mEmailET.setError("Invalid Email");
mEmailET.setFocusable(true);
}else if (password.length()<6){
//set error and focus to password
mPassword.setError("Password length must be at least 6 characters");
mPassword.setFocusable(true);
}else{
//register the user
registerUser(email,password);
}
}
});
}
private void registerUser(String email, String password){
//email and password is valid ,shows progress dialog and start registering user
progressDialog.show();
mAuth.createUserWithEmailAndPassword(email,password)
.addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
@Override
public void onComplete(@NonNull Task<AuthResult> task) {
if (task.isSuccessful()) {
// Sign in success, dismiss dialog and start register activity
progressDialog.dismiss();
FirebaseUser user = mAuth.getCurrentUser();
assert user != null;
Toast.makeText(RegisterActivity.this,"Registered..."+user.getEmail(), Toast.LENGTH_SHORT).show();
startActivity(new Intent(RegisterActivity.this, ProfileActivity.class));
finish();
} else {
// If sign in fails, display a message to the user.
progressDialog.dismiss();
Toast.makeText(RegisterActivity.this, "Authentication failed.", Toast.LENGTH_SHORT).show();
}
}
}) .addOnFailureListener(new OnFailureListener() {
@Override
public void onFailure(@NonNull Exception e) {
//error, dismiss progrss dialog and get and show error message
progressDialog.dismiss();
Toast.makeText(RegisterActivity.this,""+e.getMessage(),Toast.LENGTH_SHORT).show();
}
});
}
@Override
public boolean onSupportNavigateUp() {
onBackPressed(); //go previous activity on clicking back
return super.onSupportNavigateUp();
}
}
我已经验证了我的xml文件的名称是相同的。
由于从activity_main.xml布局(MainActivity的视图(和RegisterActivity(activity_register.xml 的视图中有另一个注册按钮(引用注册按钮而出现错误
很抱歉浪费你的时间。activity_main中的register按钮因此没有在register.java 中初始化