java - 为什么文本未显示在 textView_1 中且运算符不起作用

Question

我正在为Android制作一个计算器。在添加代码以将文本显示到 textView_1 之前，一切都工作正常，但之后文本都不会显示在 textView_1 中，任何操作符都无法工作。

package com.example.anunay.basiccalculator1;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.lang.*;

public class MainActivity extends AppCompatActivity {

    Button button_0, button_1, button_2, button_3, button_4, button_5, button_6, button_7, button_8,
            button_9, button_Deci, button_Equal, button_Add, button_Sub, button_Mul, button_Div,
            button_Back, button_Expo, button_Sqrt, button_Clear;


    TextView textView_1, textView_2;

    float mValue1, mValue2;

 //   double mValue3;

    String mString1, mString2, mString2_Rev, textView_1Value;

    boolean mAddition = false, mSubtraction = false, mMultiplication = false, mDivision = false,
            mEqualPressed = false, mSqrt = false, mExponential = false;

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

        button_0 = (Button) findViewById(R.id.button0);
        button_1 = (Button) findViewById(R.id.button1);
        button_2 = (Button) findViewById(R.id.button2);
        button_3 = (Button) findViewById(R.id.button3);
        button_4 = (Button) findViewById(R.id.button4);
        button_5 = (Button) findViewById(R.id.button5);
        button_6 = (Button) findViewById(R.id.button6);
        button_7 = (Button) findViewById(R.id.button7);
        button_8 = (Button) findViewById(R.id.button8);
        button_9 = (Button) findViewById(R.id.button9);
        button_Deci = (Button) findViewById(R.id.buttonDeci);
        button_Add = (Button) findViewById((R.id.buttonAdd));
        button_Sub = (Button) findViewById(R.id.buttonSub);
        button_Mul = (Button) findViewById(R.id.buttonMul);
        button_Div = (Button) findViewById(R.id.buttonDiv);
        button_Sqrt = (Button) findViewById(R.id.buttonSqrt);
        button_Expo = (Button) findViewById(R.id.buttonExpo);
        button_Back = (Button) findViewById(R.id.buttonBack);
        button_Clear = (Button) findViewById(R.id.buttonClear);
        button_Equal = (Button) findViewById(R.id.buttonEqual);

        textView_2 = (TextView) findViewById(R.id.textView2);



        button_0.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mEqualPressed) {
                    textView_2.setText("0");
                    textView_1.setText(" ");

                }
                else textView_2.setText(textView_2.getText()+"0");
                mEqualPressed = false;
            }
        });

        button_1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mEqualPressed) {
                    textView_2.setText("1");
                    textView_1.setText(" ");

                }
                else textView_2.setText(textView_2.getText()+"1");
                mEqualPressed = false;
            }
        });

        button_2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mEqualPressed) {
                    textView_2.setText("2");
                    textView_1.setText(" ");

                }
                else  textView_2.setText(textView_2.getText()+"2");
                mEqualPressed = false;
            }
        });

        button_3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mEqualPressed) {
                    textView_2.setText("3");
                    textView_1.setText(" ");

                }
                else  textView_2.setText(textView_2.getText()+"3");
                mEqualPressed = false;
            }
        });

        button_4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mEqualPressed) {
                    textView_2.setText("4");
                    textView_1.setText(" ");

                }
                else  textView_2.setText(textView_2.getText()+"4");
                mEqualPressed = false;
            }
        });

        button_5.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mEqualPressed) {
                    textView_2.setText("5");
                    textView_1.setText(" ");

                }
                else  textView_2.setText(textView_2.getText()+"5");
                mEqualPressed = false;
            }
        });

        button_6.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mEqualPressed) {
                    textView_2.setText("6");
                    textView_1.setText(" ");

                }
                else  textView_2.setText(textView_2.getText()+"6");
                mEqualPressed = false;
            }
        });

        button_7.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mEqualPressed) {
                    textView_2.setText("7");
                    textView_1.setText(" ");

                }
                else  textView_2.setText(textView_2.getText()+"7");
                mEqualPressed = false;
            }
        });

        button_8.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mEqualPressed) {
                    textView_2.setText("8");
                    textView_1.setText(" ");

                }
                else  textView_2.setText(textView_2.getText()+"8");
                mEqualPressed = false;
            }
        });

        button_9.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mEqualPressed) {
                    textView_2.setText("9");
                    textView_1.setText(" ");

                }
                else   textView_2.setText(textView_2.getText()+"9");
                mEqualPressed = false;
            }
        });

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

                if(mEqualPressed) {
                    textView_2.setText(".");
                    textView_1.setText(" ");

                }
                else  textView_2.setText(textView_2.getText()+".");
                mEqualPressed = false;
            }
        });

        button_Add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (textView_2.getText()==""){
                    textView_2.setText("");
                }
                else if (textView_2.getText()=="-")
                    textView_2.setText(" ");

                else
                {
                    textView_1.setText(textView_2.getText().toString()+"+");
                mValue1 = Float.parseFloat(textView_2.getText() + "");
                mAddition = true;
                textView_2.setText(null);
                mEqualPressed = false;}
            }
        });

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

                if (textView_2.getText()==""){
                    textView_2.setText("-");
                }
                else if (textView_2.getText()=="-")
                    textView_2.setText("-");
                else{
                 textView_1.setText(textView_2.getText().toString()+"-");
                mValue1 = Float.parseFloat(textView_2.getText() + "");
                mSubtraction = true;
                textView_2.setText(null);
                mEqualPressed = false;}
            }
        });

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

                if (textView_2.getText()==""){
                    textView_2.setText("");
                }
                else if (textView_2.getText()=="-")
                    textView_2.setText(" ");
                else{
                    textView_1.setText(textView_2.getText().toString()+"*");
                mValue1 = Float.parseFloat(textView_2.getText() + "");
                mMultiplication = true;
                textView_2.setText(null);
                mEqualPressed = false;}
            }
        });

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

                if (textView_2.getText()==""){
                    textView_2.setText("");
                }
                else if (textView_2.getText()=="-")
                    textView_2.setText(" ");
                else{
                 textView_1.setText(textView_2.getText().toString()+"/");
                mValue1 = Float.parseFloat(textView_2.getText() + "");
                mDivision = true;
                textView_2.setText(null);
                mEqualPressed = false;}
            }
        });

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

                mEqualPressed = false;
                mSqrt = true;
            }
        });

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

                if (textView_2.getText()==""){
                    textView_2.setText("");
                }
                else{
                  textView_1.setText(textView_2.getText()+"^");
                mValue1 = Float.parseFloat(textView_2.getText() + "");
                mExponential = true;
                textView_2.setText(null);
                mEqualPressed = false;}

            }
        });

        button_Back.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (textView_2.getText().length()<=1)
                    textView_2.setText(" ");
                else
                    textView_2.setText((textView_2.getText()).subSequence(0, (textView_2.getText()).length()-1));


            }
        });

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

                textView_2.setText(" ");
                mEqualPressed = false;

            }
        });

        button_Equal.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mValue2 = Float.parseFloat(textView_2.getText() + "");

                textView_1.setText(textView_1.getText() + textView_2.getText().toString());

                if (mAddition){

                    textView_2.setText(mValue1 + mValue2 +"");
                    mAddition=false;
                }


                if (mSubtraction){
                    textView_2.setText(mValue1 - mValue2+"");
                    mSubtraction=false;
                }

                if (mMultiplication){
                    textView_2.setText(mValue1 * mValue2+"");
                    mMultiplication=false;
                }

                if (mDivision){
                    textView_2.setText(mValue1 / mValue2+"");
                    mDivision=false;
                }

                if (mSqrt){

                    textView_2.setText(Math.sqrt((double)mValue2)+"");
                    mSqrt = false;

                }

                if (mExponential ){

                    textView_2.setText(Math.pow((double) mValue1, (double)mValue2)+"");
                    mExponential = false;
                }

                mEqualPressed = true;
            }
        });


    }
}

Answer 1

您添加了此内容

  textView_2 = (TextView) findViewById(R.id.textView2);

但忘记初始化textView_1的引用。