Android Studio - 當 TextView 位於自定義 xml 文件時嘗試使用代碼更改它的屬性時，應用程序崩潰

Question

基本上，我試圖通過編碼更改 TextView 屬性，當我嘗試使用 MainActivity.java 應用程序中的代碼更改文本字體、顏色或任何內容時，此 TextView 位於我創建的名為 popup.xml 的自定義 xml 中將因錯誤而崩潰： java.lang.RuntimeException: Unable to start activity和java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference

來自 TextView 的錯誤：

     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
        at com.dragoonshimizu.realtest.MainActivity.onCreate(MainActivity.java:31)
        at android.app.Activity.performCreate(Unknown Source:16)
        at android.app.Activity.performCreate(Unknown Source:1)
        at android.app.Instrumentation.callActivityOnCreate(Unknown Source:3)
        at android.app.ActivityThread.performLaunchActivity(Unknown Source:368)

MainActivity.java（由 Mike M 代碼更新）：

package com.example.test;

import android.os.Bundle;
import android.os.CountDownTimer;
import android.support.v7.app.AppCompatActivity;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.PopupWindow;
import android.widget.RelativeLayout;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private PopupWindow popupWindow;
    private LayoutInflater layoutInflater;
    private RelativeLayout relativelayout;

    private TextView textYouLose;
    private TextView countTimeText;

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

        relativelayout = (RelativeLayout) findViewById(R.id.relative);
        textYouLose = (TextView) findViewById(R.id.textYouLose);

        View popupView = getLayoutInflater().inflate(R.layout.popup, null);
        textYouLose = popupView.findViewById(R.id.textYouLose);
        popupView.findViewById(R.id.popupLayout);
        textYouLose.setText("ABC");
        PopupWindow popup = new PopupWindow(popupView);
        popup.setContentView(popupView);


        startCounting();
    }


        public void startCounting() {
            countTimeText = (TextView) findViewById(R.id.countTimeText);
            new CountDownTimer(5000, 1000) {

                public void onTick(long millisUntilFinished) {
                    countTimeText.setText("Time Left: " + millisUntilFinished / 1000);
                }

                // On Finish PopupWindow
                public void onFinish() {
                    // textYouLose.setText("Error Here!");
                    countTimeText.setText("TimeUp!");
                    layoutInflater = (LayoutInflater) getApplicationContext().getSystemService(LAYOUT_INFLATER_SERVICE);
                    ViewGroup container = (ViewGroup) layoutInflater.inflate(R.layout.popup, null);
                    // Adding true will make it closable if clicked outside window
                    popupWindow = new PopupWindow(container, 1080, 1920, true);
                    popupWindow.showAtLocation(relativelayout, Gravity.NO_GRAVITY, 500, 500);

                    container.setOnTouchListener(new View.OnTouchListener() {
                        @Override
                        public boolean onTouch(View view, MotionEvent motionEvent) {
                            popupWindow.dismiss();
                            return true;
                        }
                    });
                }
            }.start();

        }

    }

popup.xml :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#E16A6A"
    android:id="@+id/popupLayout"
    android:orientation="vertical">

    <TextView
        android:id="@+id/textYouLose"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:layoutDirection="rtl"
        android:text="You lose!"
        android:textAlignment="center"
        android:textSize="40dp" />
</RelativeLayout>

目前，該應用程序不會因更新的代碼而崩潰，但也不會將文本更改為我將其設置為“ABC”的內容。

Answer 1

膨脹的視圖activity_main.xml不包含任何Textview與@+id/textYouLose 。

只需在您的activity_main.xml復制/粘貼您的 texview 代碼：

<TextView
        android:id="@+id/textYouLose"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:layoutDirection="rtl"
        android:text="You lose!"
        android:textAlignment="center"
        android:textSize="40dp" />