Question

我尝试编写一个应用示例，以检查来自String 1的用户输入（EditText）并将其与字符串（在这种情况下为translation 1）进行比较。

在回答和提出建议之后，我已经更新了Java代码，据我所知我应该可以正常工作，但我不能。（请参见调试器编辑）

谢谢！

XML：

<?xml version="1.0" encoding="utf-8"?>

<android.support.constraint.ConstraintLayout 

xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<!-- Page Title -->
<TextView
    android:id="@+id/PageTitle"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:text="@string/test_title"
    android:textAlignment="center"
    android:textSize="24sp"
    android:textStyle="bold"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.5"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<!-- Input 1 -->
<EditText
    android:id="@+id/input1"
    android:layout_width="140dp"
    android:layout_height="40dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:inputType="text"
    android:text=""
    android:hint="@string/hint_input"
    app:layout_constraintEnd_toStartOf="@+id/translation1"
    app:layout_constraintHorizontal_bias="0.5"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/PageTitle"
    android:imeOptions="actionNext"/>

<!-- Translation 1 -->
<TextView
    android:id="@+id/translation1"
    android:layout_width="140dp"
    android:layout_height="40dp"
    android:layout_marginEnd="8dp"
    android:layout_marginTop="8dp"
    android:gravity="center"
    android:text="@string/test"
    android:textAlignment="center"
    android:textSize="18sp"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.5"
    app:layout_constraintStart_toEndOf="@+id/input1"
    app:layout_constraintTop_toBottomOf="@+id/PageTitle"
    android:background="@drawable/translation_borders"/>

<!--Check button-->
<Button
    android:id="@+id/button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:onClick="Check"
    android:text="@string/check_btn"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="@+id/translation1"
    app:layout_constraintStart_toStartOf="@+id/input1"
    app:layout_constraintTop_toBottomOf="@+id/PageTitle" />

</android.support.constraint.ConstraintLayout>

编辑：更新代码。

Java：

package com.bnf.Overhooring;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

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

    String right = getString(R.string.right);
    String wrong = getString(R.string.wrong);

    EditText input1 = (EditText) findViewById(R.id.input1);
    String string1 = input1.getText().toString();
    String translation1 = "a";

    public void Check(View view) {
        if (string1.equals(translation1)) input1.setText(right);
        else input1.setText(wrong);
    }
}

编辑：发布调试器结果

更新代码后，我已经运行了调试器，发现我的应用在启动时一直关闭。调试器中的错误：

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.bnf.overhooring, PID: 471
              java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.bnf.overhooring/com.bnf.overhooring.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2849)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045)
                  at android.app.ActivityThread.-wrap14(ActivityThread.java)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:154)
                  at android.app.ActivityThread.main(ActivityThread.java:6776)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1496)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1386)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
                  at android.content.ContextWrapper.getResources(ContextWrapper.java:86)
                  at android.view.ContextThemeWrapper.getResourcesInternal(ContextThemeWrapper.java:127)
                  at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:121)
                  at android.support.v7.app.AppCompatActivity.getResources(AppCompatActivity.java:542)
                  at android.content.Context.getString(Context.java:476)
                  at com.bnf.overhooring.MainActivity.<init>(MainActivity.java:16)
                  at java.lang.Class.newInstance(Native Method)
                  at android.app.Instrumentation.newActivity(Instrumentation.java:1086)
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2839)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045) 
                  at android.app.ActivityThread.-wrap14(ActivityThread.java) 
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642) 
                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                  at android.os.Looper.loop(Looper.java:154) 
                  at android.app.ActivityThread.main(ActivityThread.java:6776) 
                  at java.lang.reflect.Method.invoke(Native Method) 
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1496) 
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1386)

Answer 1

如果要在移动屏幕上进行视觉确认，则可以让TextView或EditText进行显示。您可以使用EditText input1将文本设置为setText()。

例如：input1.setText("Text");

TextView translation = (TextView) findViewById(R.id.translation1); 
translation.setText(input1.getText().toString());

您可以使用以下方法设置OnClickListener：

Button btn = findViewById(R.id.button);
btn.setOnClickListener(new OnClickListener() {
    public void onClick(View v) {
        //Your code goes here
   } 
});

这将从edittext中获取值进行比较，并基于textview中的值设置文本

public class MainActivity extends AppCompatActivity {

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

      EditText input1 = (EditText) findViewById(R.id.input1);

      String String1 = input1.getText().toString();

      String translation1 = "a";

      Button btn = findViewById(R.id.button);

      btn.setOnClickListener(new OnClickListener() {
      public void onClick(View v) {

          if(String1.equals(translation1)) {
              //System.out.print("This right!");
              translation.setText("This right!");
          } else {
              //System.out.print("This is wrong!");
              translation.setText("This wrong!"); 
          }
       } 
   }
}

Answer 2

我要指出的一些错误：

请勿为{ }使用单独的块if-else
请勿将System.out.println()用于Android开发，请尝试使用Log.i()或任何其他Log语句。
从视觉显示开始，尝试使用EditText.setText()或TextView.setText()函数在您的情况下显示视觉输出。
要遵循上述观点，您首先需要通过View初始化相应的TextView（例如EditText或findViewById()以使用setText()或{{ 1}}。

编辑：由于您的代码应在活动从版式膨胀时运行，因此请将代码放在getText()中的setContentView()之后

我建议您通过official developer guide进行推荐。

Android：带有string.equals的if / else语句，返回视觉确认

2 个答案: