当方向改变时 EditTexts 不起作用？

Question

I am needing to reformat an existing Android app to have a landscape version. It uses a TextWatcher to calculate a tip amount when numbers are entered into 2 EditTexts (bill amount & tip percent). It works by itself, but when I add a second layout, the TextWatcher stops working and doesn't calculate anything. It rotates and looks how I want it to, but doesn't function. My landscape layout has all the same parts as the portrait with the same EditText & TextView IDs. This is what I am using to change the layouts:

package com.example.tiporientation;

import androidx.appcompat.app.AppCompatActivity;

import android.content.res.Configuration;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.util.Log;
import android.widget.EditText;
import android.widget.TextView;
import java.text.NumberFormat;

public class MainActivity extends AppCompatActivity {

    private TipCalculator tipCalc;
    private NumberFormat money = NumberFormat.getCurrencyInstance();
    private EditText billEditText;
    private EditText tipEditText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        tipCalc = new TipCalculator(.17f,100);
        setContentView(R.layout.activity_main);

        billEditText = findViewById(R.id.EDIT_BillAmount);
        tipEditText = findViewById(R.id.EDIT_EnterTip);

        //create inner-class for this... puts it at bottom of MainActivity
        //TextChangeHandler is a "listener"
        //attach it to our EDIT texts, so it is listening to changes in bill $ & tip %
        TextChangeHandler tch = new TextChangeHandler();
        billEditText.addTextChangedListener(tch);
        tipEditText.addTextChangedListener(tch);
        Configuration config = getResources().getConfiguration();
        modifyLayout(config);
    }

    private void modifyLayout(Configuration newConfig) {
        if(newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE)
            setContentView(R.layout.activity_main_landscape); //we create new XML for this layout
        else if(newConfig.orientation == Configuration.ORIENTATION_PORTRAIT)
            setContentView(R.layout.activity_main);
    }

    public void onConfigurationChanged(Configuration newConfig) {
        Log.w("MainActivity", "Inside onConfigurationChanged");
        super.onConfigurationChanged(newConfig);
        modifyLayout(newConfig); //if orientation changes again, send back to modifyLayout
    }

    public void calculate () {
        //convert edit texts to a string ???
        String billString = billEditText.getText().toString();
        String tipString = tipEditText.getText().toString();

        //2 text views from XML
        TextView tipTextView = findViewById(R.id.TXT_TipTotal);
        TextView totalTextView = findViewById(R.id.TXT_TotalAmount);

        try {
            //convert billString to float & tipString to int -- can't do math with strings
            float billAmount = Float.parseFloat(billString);
            int tipPercent = Integer.parseInt(tipString);
            //update the model -- referencing TipCalculator class!
            tipCalc.setBill(billAmount);
            tipCalc.setTip(.01f * tipPercent);
            //ask model to calculate
            float tip = tipCalc.tipAmount();
            float total = tipCalc.totalAmount();
            //update view with formatted tip & total amount
            tipTextView.setText(money.format(tip));
            totalTextView.setText(money.format(total));
        } catch(NumberFormatException nfe) { }
    }

    //create implements... select all 3 they are then stubbed out in the class
    private class TextChangeHandler implements TextWatcher {
        @Override
             public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        }
        @Override
             public void onTextChanged(CharSequence s, int start, int before, int count) {
        }
        @Override
             public void afterTextChanged(Editable s) {
             calculate();
        }
    }
}

Manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.tiporientation">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity"
            android:configChanges="orientation|screenSize">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Answer 1

With the onConfigurationChanged callback your activity is destroyed and re-created. Values in your text fields can be stored in the savedInstanceState and then retrieved in onCreate.

I am not entirely sure, but I think what happens here is:

• Phone rotates
• Phone recreates the activity (your onCreate runs)
• you receive the onConfiguration callback
• there you assign a new contentView(_landscape)
• and with this you destroy the layout just rendered in onCreate and your listeners

Your onCreate has already run, thus your TextWatcher was attached to a layout you just destroyed with your setContentView call from modifyLayout .

I still think you should let android manage this for you, but to solve the problem, I suggest:

• remove the code from onCreate beginning with the first findViewById up to (and including) the .addTextWatcher lines

• remove the other clutter with an additional modifyLayout call from your onCreate

• put this code in a method, say connectWatchers

• call this method from onCreate

• call this method from modifyLayout

It should look like this:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    tipCalc = new TipCalculator(.17f,100);
    setContentView(R.layout.activity_main);
    connectWatchers();
}

private void modifyLayout(Configuration newConfig) {
    if(newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE)
        setContentView(R.layout.activity_main_landscape); //we create new XML for this layout
    else if(newConfig.orientation == Configuration.ORIENTATION_PORTRAIT)
        setContentView(R.layout.activity_main);

    connectWatchers();
}

public void onConfigurationChanged(Configuration newConfig) {
    Log.w("MainActivity", "Inside onConfigurationChanged");
    super.onConfigurationChanged(newConfig);
    modifyLayout(newConfig); //if orientation changes again, send back to modifyLayout
}

private void connectWatchers() {
    billEditText = findViewById(R.id.EDIT_BillAmount);
    tipEditText = findViewById(R.id.EDIT_EnterTip);
    TextChangeHandler tch = new TextChangeHandler();
    billEditText.addTextChangedListener(tch);
    tipEditText.addTextChangedListener(tch);
}