"Button button1 = (Button)findViewById(R.id.button_1) "在安卓中运行

Question

我是Android的初学者，所以请原谅我的无知。在我学习Android编程时，我遵循了这本书，代码如下:

FirstActivity.java

package com.example.activitytest;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
public class FirstActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.first_layout);
Button button1 = (Button)findViewById(R.id.button_1);
button1.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v){
Toast.makeText(FirstActivity.this, "You clicked Button 1", Toast.LENGTH_SHORT).show();
}
});
}
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.activitytest">
<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/Theme.Activitytest">
<activity
android:name=".FirstActivity"
android:label="This is FirstActivity"
android:exported="true">
<intent-filter>
<action android:name = "android.intent.action.MAIN"/>
<category android:name = "android.intent.category.LAUNCHER"/>
</intent-filter>
</activity>
</application>
</manifest>

first_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/button_1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/button_1"
tools:ignore="MissingConstraints"
tools:layout_editor_absoluteX="0dp"
tools:layout_editor_absoluteY="1dp" />
</androidx.constraintlayout.widget.ConstraintLayout>

android studio报告:

error: cannot find symbol
Button button1 = (Button)findViewById(R.id.button_1);
^
symbol:   class Button
location: class FirstActivity

，然后我搜索stackoverflow来找到要调试的方法。我曾经尝试过这个方法:

View rootView = inflater.inflate(R.layout.fragment_main, container, false);
Button buttonClick = (Button)rootView.findViewById(R.id.button);
buttonClick.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
onButtonClick((Button) view);
}
});

但它仍然不起作用。由于我只是一个初学者，我找不到调试的方法。有人能帮帮我吗?谢谢你。

Answer 1

从你的代码中可以看到在xml中你为按钮指定了id也就是

android:id="@+id/button_1"

但是你试图访问错误的id

Button buttonClick = (Button)rootView.findViewById(R.id.button);

如果您正在活动，则不需要rootView，您可以简单地使用findViewById(R.id.button_1)访问按钮

在你的first_layout.xml

tools:context=".FirstActivity"

将此添加到xml中的constraintLayout

也添加import

import android.widget.Button;

我建议你使用viewBinding在这种情况下它会帮助你很多

Answer 2

add this line

import android.widget.Button;

FirstActivity.java

package com.example.activitytest;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
import android.widget.Button;
public class FirstActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.first_layout);
Button button1 = (Button)findViewById(R.id.button_1);
button1.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v){
Toast.makeText(FirstActivity.this, "You clicked Button 1", Toast.LENGTH_SHORT).show();
}
});
}
}