尝试在空对象引用上调用虚拟方法“java.lang.CharSequence android.widget.TextView.getText()”

Question

我得到了这个空异常：

java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“java.lang.CharSequence android.widget.TextView.getText()”

我不知道为什么。

protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setTheme(R.style.LoginRegister);
        setContentView(R.layout.activity_report);

final TextView infoid = (TextView) findViewById(R.id.idInfo);

        RadioGroup rg = (RadioGroup)findViewById(R.id.rg);
        final String radiovalue = ((RadioButton)findViewById(rg.getCheckedRadioButtonId())).getText().toString();

...

        Button sendButton = (Button) findViewById(R.id.button2);
        sendButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String text = infoid.getText().toString(); //what is wrong?
                Log.w("message: ", radiovalue);
            }
        });


}

我的 xml

   <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/idInfo"
        android:hint="Add some extra information"
        android:layout_weight="0.09"
        android:layout_marginTop="20dp"
        android:layout_marginBottom="20dp" />

    <Button
        android:text="Report"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/button2" />

有什么想法吗？

Answer 1

1. 确保TextView idInfo 存在于您的activity_report.xml 中

2. 尝试将idInfo 声明为全局。

   ..............
   ....................
   
   TextView infoid;
   
   protected void onCreate(Bundle savedInstanceState) {
   
       super.onCreate(savedInstanceState);   
       setContentView(R.layout.activity_report);
   
       infoid = (TextView) findViewById(R.id.idInfo);
   
       .............
       ...................
   
       Button sendButton = (Button) findViewById(R.id.button2);
       sendButton.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View view) {
               String text = infoid.getText().toString();
               ..........
               .................
           }
       });
   
   }
   

更新：

要选中radioButton 文字：

RadioGroup radioGroup = (RadioGroup)findViewById(R.id.rg);

// get selected radioButton from radioGroup
int selectedId = radioGroup.getCheckedRadioButtonId();

// find the radioButton by returned id
radioButton = (RadioButton) findViewById(selectedId);

// radioButton text
String radiovalue = radioButton.getText();

希望对你有帮助~

Answer 2

if (radioGroup.getCheckedRadioButtonId() <= 0) {
    Toast.makeText(yourclass, "Choose Radio Button Please", Toast.LENGTH_SHORT).show();
}

Answer 3

check this

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Toast;

public class MyAndroidAppActivity extends Activity {

  private RadioGroup radioGroup;
  private RadioButton radioButton;
  private Button btnDisplay;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    addListenerOnButton();

  }

  public void addListenerOnButton() {

    radioGroup = (RadioGroup) findViewById(R.id.radio);
    btnDisplay = (Button) findViewById(R.id.btnDisplay);

    btnDisplay.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {

                // get selected radio button from radioGroup
            int selectedId = radioGroup.getCheckedRadioButtonId();

            // find the radiobutton by returned id
            radioButton = (RadioButton) findViewById(selectedId);

            Toast.makeText(MyAndroidAppActivity.this,
                radioButton.getText(), Toast.LENGTH_SHORT).show();

        }

    });

  }
}