You have some small mistakes in the code, but do not worry, I'll try to explain them as best as possible:
It turns out that if you want the button to add and save when you press the button, you are doing it wrong, because for a button to be linked to the action, it can be done in several ways:
NOTE: if you already know the ways to link an action with a button, go to the section of SharedPreferences , just under the explanation of the buttons.
LINK A METHOD TO A BUTTON
This way you have to create a method in your code Java and from the properties of the button in the section XML of Desing , you would have to look for a property called onClick and assign there the method that you have created. You do not need to pass any View to this method as you do in the a() method
IMPLEMENT THE ONCLICKLISTENER METHOD
To do this, you have two ways:
-
In your declaration of the main class you add the following and implement the necessary codes:
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
Button b1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
b1 = (Button) findViewById(R.id.b1);
// Así se enlaza el botón a el método
b1.setOnClickListener(this);
}
@Override
public void onClick(View v) {
// Método necesario de implementar
// Para saber que botón se pulsa en caso de tener más de uno
switch (v.getId()){
case R.id.b1:
// Añadir aquí el código que quieras que funcione cuando se presione el botón
break;
}
}
}
-
The other way, is to implement it directly to your button in the onCreate() method:
public class MainActivity extends AppCompatActivity{
Button b1;
TextView tv3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
b1 = (Button) findViewById(R.id.btGuardar);
// Implementación de la ación del botón
b1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//Acciones que quieras que realice el botón
}
});
}
}
Once you know this, I'll explain the SharedPreferences and understand why you fail:
SHAREDPREFERENCES
-
To get a value of SharedPreferences this code is used:
SharedPreferences preferences = getSharedPreferences ("Balance", Context.MODE_PRIVATE);
textview.setText (preferences.getString ("Value", "5"));
The first line declares the file of SharedPreferences that will be accessed. In this case it will be called Saldo . When this line is executed, on your Android device a file called Saldo will be created, which you will access whenever you declare the first line, no matter what Activity (screen) you are.
In the second line you are saying to add a value to TextView that is stored with the code name Valor and that in case the key Valor does not exist, it will be created and its initial value will be 5 .
You in your app, you have set "" , so you will NEVER get anything or add anything and you will execute the action, but the value is still "" , that is, nothing.
-
If you want to save, the following code is executed, as you have in your code:
SharedPreferences preferences = getSharedPreferences("Saldo", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.putString("Valor", String.valueOf(tv3.getText()));
editor.apply();
Try using apply() to save the data instead of commit() .
Now you know the reason for your error and I leave you an example code that I have made:
MainActivity.java
public class MainActivity extends AppCompatActivity implements View.OnClickListener{
Button b1;
TextView tv3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
b1 = (Button) findViewById(R.id.btGuardar);
tv3 = (TextView) findViewById(R.id.tvNumero);
SharedPreferences preferences = getSharedPreferences("Saldo", Context.MODE_PRIVATE);
tv3.setText(preferences.getString("Valor", "5"));
b1.setOnClickListener(this);
}
public void onClick(View v) {
switch (v.getId()){
case R.id.btGuardar:
int x = 200;
String valor1 = (String) tv3.getText();
int num1 = Integer.parseInt(valor1);
int sumar = num1 + x;
String resultado = String.valueOf(sumar);
tv3.setText(resultado);
SharedPreferences preferences = getSharedPreferences("Saldo", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.putString("Valor", String.valueOf(tv3.getText()));
editor.apply();
break;
}
}
}
activity_main.xml :
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.victoriavicent.myapplication.MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="@string/_5"
android:id="@+id/tvNumero"
android:layout_alignParentTop="true"
android:layout_alignParentStart="true"
android:layout_above="@+id/btGuardar"
android:layout_alignParentEnd="true"
android:gravity="center"
android:textSize="50sp"
android:textColor="@android:color/black" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/guardar"
android:id="@+id/btGuardar"
android:layout_alignParentBottom="true"
android:layout_alignParentStart="true"
android:layout_alignParentEnd="true" />
</RelativeLayout>
I hope you have made everything clear, but even so, if you need anything or do not just understand something that I just explained, write me a comment and I'll solve the question.
Good luck with your app!