第二个活动上的 Android Studio 我的按钮不起作用

Question

I think it a very easy Question. I am new to Android Studio and I could not find an answer.

I have an activity that switches per Button to another activity. However, on my second activity, my simple Button just to change the Textview which doesn't work.

Layout

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".StartActivity">

    <TextView
        android:id="@+id/twText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="127dp"
        android:layout_marginLeft="127dp"
        android:layout_marginTop="88dp"
        android:layout_marginEnd="127dp"
        android:layout_marginRight="127dp"
        android:layout_marginBottom="624dp"
        android:text="Ihr Passwort war Richtig!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />


    <Button
        android:id="@+id/btnChecke"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="134dp"
        android:layout_marginLeft="134dp"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="189dp"
        android:layout_marginRight="189dp"
        android:layout_marginBottom="371dp"
        android:text="Check"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        />

</androidx.constraintlayout.widget.ConstraintLayout>

onCreate method in my second activity

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_start);

    tw = findViewById(R.id.twText);
    btnCheck = findViewById(R.id.btnChecke);

    btnCheck.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            tw.setText("work");
        }
    });
}

And this is how I am starting the second activity ( onCreate method from my first activity).

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_start);

    tw = findViewById(R.id.twText);
    Button btnCheck = findViewById(R.id.btnChecke);

    btnCheck.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            setContentView("Work"R.layout.activity_main);
        }
    });
}

I have checked the variable names in the layout and looks like everything is fine.

Thank you in advance.

Answer 1

This answer is based on the problem which I found before the latest edit from the OP. Here is the version of the edit where I found the problem.

First of all, something is very wrong about the onClickListener of your button. You are setting the content view again, instead of starting your second activity. It looks like, you are just setting the content view of your StartActivity which actually does not launch the MainActivity that you are trying to start.

In order to start a new activity, you need to add the following in your button onClickListener .

btnCheck.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        // setContentView(R.layout.activity_main); // This is not the way for starting another activity 

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

Once your MainActivity has started, you should be able to change the text with no problem.

Answer 2

Bundle bundle = getIntent().getExtras()
if(bundle.getString("changeTextView")
TextView .... = (TextView) ....setText();

Hi. If I good understand, you should use Intent with "putExtra()". Exmple: intent.putExtras("changeTextView"); After that in your onCreate() method you can put: