Question

我正在尝试创建一个应用。测试时，每当我尝试按下按钮时，手机上的应用程序都会显示，＃34;不幸的是，[应用程序名称]已经停止。＆＃34;

在logcat上，会显示一条消息：

E/AndroidRuntime: FATAL EXCEPTION: main
 Process: com.example.inspiron.firstapplication, PID: 6746
 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.inspiron.firstapplication/com.example.inspiron.firstapplication.Text}: java.lang.NullPointerException
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2321)
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2507)
     at android.app.ActivityThread.access$900(ActivityThread.java:172)
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308)
     at android.os.Handler.dispatchMessage(Handler.java:102)
     at android.os.Looper.loop(Looper.java:146)
     at android.app.ActivityThread.main(ActivityThread.java:5692)
     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:1291)
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
     at dalvik.system.NativeStart.main(Native Method)
  Caused by: java.lang.NullPointerException
     at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:68)
     at android.support.v7.app.AppCompatDelegateImplV7.<init>(AppCompatDelegateImplV7.java:146)
     at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:28)
     at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:41)
     at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:190)
     at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:172)
     at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:512)
     at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:184)
     at com.example.inspiron.firstapplication.Text.<init>(Text.java:17)
     at java.lang.Class.newInstanceImpl(Native Method)
     at java.lang.Class.newInstance(Class.java:1208)
     at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2312)
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2507) 
     at android.app.ActivityThread.access$900(ActivityThread.java:172) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:146) 
     at android.app.ActivityThread.main(ActivityThread.java:5692) 
     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:1291) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107) 
     at dalvik.system.NativeStart.main(Native Method)

我的XML看起来像这样：

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="English:"
    android:id="@+id/LanguageTranslatedFrom"
    android:layout_alignParentTop="true"
    android:layout_alignParentStart="true"
    android:textSize="20dp" />

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/TextBar"
    android:layout_below="@+id/LanguageTranslatedFrom"
    android:layout_toEndOf="@+id/LanguageTranslatedFrom"
    android:hint="PUT IN what you want to translate..." />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Spanish:"
    android:id="@+id/LanguageTranslatedTo"
    android:layout_centerVertical="true"
    android:layout_alignParentStart="true"
    android:textSize="20dp" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="OK"
    android:id="@+id/ConfirmationButton"
    android:layout_below="@+id/TextBar"
    android:layout_alignParentEnd="true"
    android:background="#61ff00" />

<ImageButton
    android:layout_width="50dp"
    android:layout_height="100dp"
    android:id="@+id/TextIcon"
    android:src="@drawable/keyboard"
    android:layout_centerVertical="true"
    android:layout_toEndOf="@+id/LanguageTranslatedTo"
    android:layout_alignParentEnd="true" />

<ImageButton
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/ViaVoiceButton"
    android:layout_below="@+id/LanguageTranslatedTo"
    android:layout_alignParentStart="true"
    android:src="@drawable/microphone"
    android:layout_toStartOf="@+id/Result" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="What the output is..."
    android:id="@+id/Result"
    android:layout_below="@+id/TextIcon"
    android:layout_toEndOf="@+id/LanguageTranslatedTo"
    android:textSize="18dp" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Retry"
    android:id="@+id/Retryit"
    android:layout_below="@+id/ConfirmationButton"
    android:layout_alignParentEnd="true"
    android:background="#61ff00" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="BACK"
    android:id="@+id/button"
    android:layout_alignParentBottom="true"
    android:layout_toStartOf="@+id/Result"
    android:background="#ff0000" />

<Spinner
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/LanguagePicker"
    android:layout_above="@+id/TextBar"
    android:layout_toEndOf="@+id/Result" />

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_above="@+id/LanguageTranslatedTo"
    android:layout_centerHorizontal="true">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="New Text"
        android:id="@+id/textView2"
        android:layout_gravity="left|top" />
</FrameLayout>

最后，我的java看起来像这样：

import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import android.view.LayoutInflater;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;

public class Text extends AppCompatActivity {
    final Context context = this;
    Button button = (Button) findViewById(R.id.ConfirmationButton);


protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.text_wall);
    Spinner spinner = (Spinner) findViewById(R.id.LanguagePicker);



    ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
            R.array.language, android.R.layout.simple_spinner_item);

    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

    spinner.setAdapter(adapter);
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            LayoutInflater li = LayoutInflater.from(context);
            View promptsView = li.inflate(R.layout.alertdialog, null);

            AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(
                    context);


            alertDialogBuilder.setView(promptsView);
            alertDialogBuilder
                    .setCancelable(false)
                    .setPositiveButton("OK",
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog,int id) {

                                    Spinner spinner = (Spinner) findViewById(R.id.LanguagePicker);
                                    String text = spinner.getSelectedItem().toString();
                                }
                            })
                    .setNegativeButton("Cancel",
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog, int id) {
                                    dialog.cancel();
                                }
                            });
            AlertDialog alertDialog = alertDialogBuilder.create();
            alertDialog.show();
        }
    });
}

}

Answer 1

在onCreate方法中移动按钮初始化。您无法在此方法之前执行此操作，因为视图未呈现且项目尚未就绪。像下面这样更改java代码：

import android.view.LayoutInflater;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;

public class Text extends AppCompatActivity {
    Context context;
    Button button;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.text_wall);
    Spinner spinner = (Spinner) findViewById(R.id.LanguagePicker);
    button = (Button) findViewById(R.id.ConfirmationButton);
    context = this; // why this? why using context when u have this?


    ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
            R.array.language, android.R.layout.simple_spinner_item);

    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

    spinner.setAdapter(adapter);
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            LayoutInflater li = LayoutInflater.from(context);
            View promptsView = li.inflate(R.layout.alertdialog, null);

            AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(
                    context);


            alertDialogBuilder.setView(promptsView);
            alertDialogBuilder
                    .setCancelable(false)
                    .setPositiveButton("OK",
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog,int id) {

                                    Spinner spinner = (Spinner) findViewById(R.id.LanguagePicker);
                                    String text = spinner.getSelectedItem().toString();
                                }
                            })
                    .setNegativeButton("Cancel",
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog, int id) {
                                    dialog.cancel();
                                }
                            });
            AlertDialog alertDialog = alertDialogBuilder.create();
            alertDialog.show();
        }
    });
}

}

在成瘾中检查您的活动是否存在于清单中。如果没有发布完整的清单请

Android Studio：FATAL EXCEPTION

1 个答案: