android - RadioButton - 检查单选按钮是否在单选组内被选中 - Android

Question

我在检查是否在我的 radiogroup 中选择了一个 radiobutton 时遇到问题，我尝试了很多方法，例如 if(rg .getCheckedRadioButtonId() == -1) 但仍然无法处理我的代码。

在我的 logcat String selectedansText = selectedans.getText().toString();在这一行中，我的 logcat 指出了问题，有人可以帮助我吗？

我也试过 .isChecked 但它不起作用。

bt.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {

         RadioButton selectedans = (RadioButton) findViewById(rg.getCheckedRadioButtonId());
         String selectedansText = selectedans.getText().toString();

         if (rg.getCheckedRadioButtonId()== -1){
             Toast.makeText(grade_four_post_test.this, 
                           "choose answer", 
                           Toast.LENGTH_LONG).show();
         } else { //do something }

PS: bt 声明正确

01-28 22:27:07.390 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at android.view.View.performClick(View.java:4463)
01-28 22:27:07.391 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at android.view.View$PerformClick.run(View.java:18770)
01-28 22:27:07.391 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at android.os.Handler.handleCallback(Handler.java:808)
01-28 22:27:07.391 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:103)
01-28 22:27:07.392 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at android.os.Looper.loop(Looper.java:193)
01-28 22:27:07.392 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:5292)
01-28 22:27:07.392 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at java.lang.reflect.Method.invokeNative(Native Method)
01-28 22:27:07.393 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at java.lang.reflect.Method.invoke(Method.java:515)
01-28 22:27:07.393 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:828)
01-28 22:27:07.393 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:644)
01-28 22:27:07.394 27612-27612/com.example.computer.mathkiddofinal:second W/System.err:     at dalvik.system.NativeStart.main(Native Method)
01-28 22:27:07.394 27612-27612/com.example.computer.mathkiddofinal:second W/dalvikvm: threadid=1: calling UncaughtExceptionHandler
01-28 22:27:07.396 27612-27612/com.example.computer.mathkiddofinal:second E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                            Process: com.example.computer.mathkiddofinal:second, PID: 27612
                                                                                            java.lang.NullPointerException
                                                                                                at com.example.computer.mathkiddofinal.grade_level.post_test.grade_four_post_test$1.onClick(grade_four_post_test.java:117)
                                                                                                at android.view.View.performClick(View.java:4463)
                                                                                                at android.view.View$PerformClick.run(View.java:18770)
                                                                                                at android.os.Handler.handleCallback(Handler.java:808)
                                                                                                at android.os.Handler.dispatchMessage(Handler.java:103)
                                                                                                at android.os.Looper.loop(Looper.java:193)
                                                                                                at android.app.ActivityThread.main(ActivityThread.java:5292)
                                                                                                at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                                at java.lang.reflect.Method.invoke(Method.java:515)
                                                                                                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:828)
                                                                                                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:644)
                                                                                                at dalvik.system.NativeStart.main(Native Method)
01-28 22:27:07.400 696-9034/system_process V/Provider/Settings:  from settings cache , name = dropbox:data_app_crash , value = null
01-28 22:27:07.401 696-9034/system_process D/dalvikvm: create interp thread : stack size=128KB
01-28 22:27:07.401 696-9034/system_process D/dalvikvm: create new thread
01-28 22:27:07.401 696-9034/system_process D/dalvikvm: new thread created
01-28 22:27:07.401 696-9034/system_process D/dalvikvm: update thread list
01-28 22:27:07.402 696-28496/system_process D/dalvikvm: threadid=79: interp stack at 0x63b53000
01-28 22:27:07.402 696-28496/system_process D/dalvikvm: threadid=79: created from interp
01-28 22:27:07.402 696-9034/system_process D/dalvikvm: start new thread
01-28 22:27:07.402 696-9034/system_process V/Provider/Settings:  from settings cache , name = send_action_app_error , value = 1
01-28 22:27:07.402 696-28496/system_process D/dalvikvm: threadid=79: notify debugger
01-28 22:27:07.403 696-9034/system_process W/ActivityManager:   Force finishing activity com.example.computer.mathkiddofinal/.grade_level.post_test.grade_four_post_test

Answer 1

您将为此获得 NullPointerException:

  RadioButton selectedans = (RadioButton) findViewById(rg.getCheckedRadioButtonId());
         String selectedansText = selectedans.getText().toString();//NullPointer

因为如果没有选择 RadioButton，findViewById 将不起作用，所以你的 RadioButton 没有被初始化。你应该这样做:

 int radioButtonId = rg.getCheckedRadioButtonId();

if(radioButtonId!=-1){

   //do Your stuff
    RadioButton selectedans = (RadioButton) findViewById(radioButtonId);
    String selectedansText = selectedans.getText().toString();

}else{
 Toast.makeText(grade_four_post_test.this, 
                           "choose answer", 
                           Toast.LENGTH_LONG).show();
}