我正在开发一个项目，当按下按钮时，该项目会用文本更新文本视图。例如，您按 0，文本视图上就会显示 0。当设备改变方向时，例如当用户旋转设备时，应用程序崩溃。
当我注释掉
button0.setOnClickListener(new Buttons(request, "0"));我已经验证在纵向和横向布局中都有一个 id 为“零”的按钮。
布局存储在：
res/layout/activity_main.xml
res/layout-land/activity_main.xml
当“.setOnclickListener()”代码行未包含在“MainActivity”中时，两种布局中都没有警告或错误消息，并且（再次）两种布局都起作用。
头等舱。 MainActivity.java:
package com.example.myapp;
import android.content.res.Configuration;
import android.os.Bundle;
import android.text.method.ScrollingMovementMethod;
import android.util.Log;
import android.widget.Button;
import android.widget.TextView;
import androidx.activity.EdgeToEdge;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;
public class MainActivity extends AppCompatActivity {
Button button0;
TextView request;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
EdgeToEdge.enable(this);
setContentView(R.layout.activity_main);
request = findViewById(R.id.request);
// Number Buttons
button0 = findViewById(R.id.zero);
button0.setOnClickListener(new Buttons(request, "0"));
ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
return insets;
});
}
}
第二类。按钮.java:
package com.example.myapp;
import android.view.View;
import android.widget.TextView;
import static androidx.core.content.res.TypedArrayUtils.getText;
public class Buttons implements View.OnClickListener {
TextView tv;
String text;
public Buttons(TextView tv, String input){
this.tv = tv;
this.text = input;
}
public Buttons(TextView tv){
this.tv = tv;
this.text = "";
}
@Override
public void onClick(View view) {
if (tv.getText().toString().equals("Request")){
tv.setText(text);
}
else {
String response = tv.getText().toString() + text;
tv.setText(response);
}
}
}
我尝试将其附加到 MainActivity.java 类：
@Override
protected void onDestroy() {
button0.setOnClickListener(null);
super.onDestroy();}
@Override
public void onConfigurationChanged(@NonNull Configuration newConfig) {
super.onConfigurationChanged(newConfig);
}
这是 Logcat：
FATAL EXCEPTION: main
Process: com.example.texascal, PID: 9311
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.texascal/com.example.texascal.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4164)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4322)
at android.app.ActivityThread.handleRelaunchActivityInner(ActivityThread.java:6499)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:6378)
at android.app.servertransaction.ActivityRelaunchItem.execute(ActivityRelaunchItem.java:76)
at android.app.servertransaction.ActivityTransactionItem.execute(ActivityTransactionItem.java:45)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:139)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:96)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2685)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loopOnce(Looper.java:230)
at android.os.Looper.loop(Looper.java:319)
at android.app.ActivityThread.main(ActivityThread.java:8919)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:578)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1103)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.texascal.MainActivity.onCreate(MainActivity.java:82)
at android.app.Activity.performCreate(Activity.java:8975)
at android.app.Activity.performCreate(Activity.java:8944)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1456)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4146)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4322)
at android.app.ActivityThread.handleRelaunchActivityInner(ActivityThread.java:6499)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:6378)
at android.app.servertransaction.ActivityRelaunchItem.execute(ActivityRelaunchItem.java:76)
at android.app.servertransaction.ActivityTransactionItem.execute(ActivityTransactionItem.java:45)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:139)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:96)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2685)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loopOnce(Looper.java:230)
at android.os.Looper.loop(Looper.java:319)
at android.app.ActivityThread.main(ActivityThread.java:8919)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:578)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1103)
2024-07-23 15:21:58.653 9311-9311 Process com.example.texascal I Sending signal. PID: 9311 SIG: 9
---------------------------- PROCESS ENDED (9311) for package com.example.texascal ----------------------------
我发现了问题。在学习如何使用 logcat 后，我发现我有针对各种设备尺寸的重复布局，以适应或响应不同的 Android 设备外形尺寸。虽然 id 为零的按钮存在于多个不同的布局中，但并非所有布局都存在。解决方案是验证 0 按钮对于每个布局都有一个 id。
<Button
...
android:text="0"
android:id="@+id/zero"/>