clear a value from a string android

问题

I have an app that lets you click buttons to add and subtract +5 or -5 and +1 or -1 from a starting value of 20. I have it set up so that when a button is clicked it will put that value into a string and display it so that the user can see a history of what they have pressed. I have a method called reset(); that resets the starting value back to 20, I would like to know how to also clear the string values

add5.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        counter += 5;
        updateDisplay();

        // add the click history for p1
        String tmText = (String) btnPressedTV.getText();
        btnPressedTV.setText(tmText + "\n" + String.valueOf(counter));
    }
});

sub5.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        counter -= 5;
        updateDisplay();

        // add the click history for p1
        String tmText = (String) btnPressedTV.getText();
        btnPressedTV.setText(tmText + "\n" + String.valueOf(counter));
    }
});

    void reset() {
    // TODO Auto-generated method stub
    counter = 20;
    display.setText(String.valueOf(20));
    display.setTextColor(Color.BLACK);
    tmText = ""; 

}

回答1:

Try this..

Use your String tmText in Global like below and as like your integer counter

String tmText;
int counter;

and reset method

public void reset()  
{
    tmText = ""; 
    counter = 20; 
}

回答2:

Make sure that the String should be class variable and not local variable.
To clear a call variable String value try this

class Sample
{
 String str; // class variable (string)
 int counter=20; // class variable (integer)
 :
 :
 :
 reset.setOnClickListener(new View.OnClickListener() {  // button click
    @Override
    public void onClick(View v) {
       str = ""; // you can clear the string value like this
       counter = 20; // you can reset the integer value like this 
    }
 });
 :
 :
 :
 public void resetfunction()  // method
 {
  str = ""; // you can clear the string value like this
  counter = 20; // you can reset the integer value like this
 }
 :
 :
 :
}

回答3:

You can reset ur String by assigning double quotes to it by

str = "";

回答4:

I suggest using implementing OnClickListener in your class. The difference explained here The different OnClickListener implementation ways

Here is some code to explain what I mean:

public class MainActivity extends Activity implements OnClickListener {

    Button add5;
    Button sub5;
    Button reset;

    int counter;
    String tmText;

    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_activity);

    //init the counter var
    counter = 20;


    //get handles to the buttons in your xml declaration
    add5 = (Button) findViewById(R.id.add5);
    sub5 = (Button) findViewById(R.id.sub5);
    reset = (Button) findViewById(R.id.reset);

    //attach the buttons the onclickListener
    add5.setOnClickListener(this);
    sub5.setOnClickListener(this);
    reset.setOnClickListener(this);

    @Override
    public void onClick(View arg0) {
        switch(arg0.getId()) {
        case R.id.add5:
            // +5 code
            break;
        case R.id.sub5:
            // minus 5 code
            break;
        case R.id.reset;
            counter = 20;
            tmText = "";
        }
    }
}

If you are looking to clear the values displayed in a textview:

TextView myTextView = (TextView) findViewById(R.id.myTextView);
myTextView.setText("");

来源：https://stackoverflow.com/questions/20736863/clear-a-value-from-a-string-android