面临主要活动困难

Question

我在尝试运行我的应用程序时遇到了一些错误这里是 logcat  java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.chatapp/com.example.chatapp.MainActivity}: java.lang.InstantiationException: java.lang.Class<com.example.chatapp.MainActivity> has no zero argument constructor    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2843)    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.InstantiationException: java.lang.Class<com.example.chatapp.MainActivity> has no zero argument constructor这是我的 mainAcivity `public class MainActivity extends AppCompatActivity {Button login, register;FirebaseUser firebaseUser;@Overrideprotected void onStart() {    super.onStart();    firebaseUser = FirebaseAuth.getInstance().getCurrentUser();    //check if user in null    if (firebaseUser != null){        Intent intent = new Intent(MainActivity.this, Main2Activity.class);        new MainActivity(intent);        finish();    }}`但我也认为这是一个错误 public MainActivity(Intent intent) {}

Answer 1

活动不需要实例化，因此只需要调用以下内容即可启动：

//check if user in null

if (firebaseUser != null){

    Intent intent = new Intent(MainActivity.this, Main2Activity.class);

    startActivity(intent);

    finish();

}

基本上你只需要删除这一行：

new MainActivity(intent);

并开始活动：

startActivity(intent);