我在简单的 android 应用程序中做错了什么？

Question

I am trying to make a app that has a switch a button and a text and if you turn the switch on and press the button; the number displayed on the text will be added by 1. But if the switch is turned off the number will be subtracted by 1. but when i run my app and press the button, the app crashes...

i do not have much experience at programming and i do not know what im doing wrong. and i have only tried this code.

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    final TextView text = (TextView)findViewById(R.id.textView);
    final Button button = (Button)findViewById(R.id.button);
    Switch mySwitch = (Switch)findViewById(R.id.mySwitch);

    mySwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                if (isChecked== true){

                    button.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {

                            String text_string = text.getText().toString();
                            int text_int = Integer.parseInt(text_string);
                            text_int++;
                            text.setText(text_int);

                        }
                    });


                }

                if (isChecked == false) {

                    button.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {

                            String text_string = text.getText().toString();
                            int text_int = Integer.parseInt(text_string);
                            text_int++;
                            text.setText(text_int);

                        }
                    });

                }
        }
    });
}

}

so this should behave as i described earlier but it doesn't.

Answer 1

You don't need a listener for the Switch , but only 1 listener for the Button :

final TextView text = (TextView)findViewById(R.id.textView);
final Button button = (Button)findViewById(R.id.button);
final Switch mySwitch = (Switch)findViewById(R.id.mySwitch);

button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        String text_string = text.getText().toString();
        int text_int = 0;
        try {
            text_int = Integer.parseInt(text_string);
        } catch (NumberFormatException e) {
            e.printStackTrace();
        }
        if (mySwitch.isChecked())
            text_int++;
        else
            text_int--;
        text.setText("" + text_int);
    }
});

Every time you click the Button , in its listener the value in the TextView is increased or decreased depending on whether the Switch is checked or not.

Answer 2

You're nesting listeners but that logic doesn't work sequentially. You should declare your listeners separately. I suggest you create a boolean that holds the state of the switch and one button listener. Within the listener check if switch is enabled then run your calculations and do the same if the switch is disabled.

    button.setOnClickListener(new View.OnClickListener() {
       @Override
       public void onClick(View v) {
       if(mySwitch.isChecked(){
           String text_string = text.getText().toString();
           int text_int = Integer.parseInt(text_string);
           text_int++;
           text.setText(String.valueOf(text_int));
        } else {
           String text_string = text.getText().toString();
           int text_int = Integer.parseInt(text_string);
           text_int++;
           text.setText(String.valueOf(text_int));
        }
      }
   });

Answer 3

Your app crashes because you are trying to set an int to a textview.setText() and when you pass an int to this method it expects it to be a resource id and which could not be found in your case that's why it will throw ResourceNotFoundException and crashes.

You should set text as following:

text.setText(String.valueOf(text_int));