当我单击首选项时，AlertDialog 崩溃

Question

我有问题。我创建了一个名为 Brightness 的类，用于通过对话框中的 SeekBar 管理屏幕的亮度。这是课堂。

public class Brightness extends Activity{

    private SeekBar brightbar;
    private int brightness;
    @SuppressWarnings("unused")
    private ContentResolver cResolver;
    private Window window;
    TextView txtPerc;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ShowDialog();

    }


    public void ShowDialog() {

    final AlertDialog.Builder popDialog = new AlertDialog.Builder(this);
    final LayoutInflater inflater = (LayoutInflater) this.getSystemService(LAYOUT_INFLATER_SERVICE);
    final View Viewlayout = inflater.inflate(R.layout.dialog_brightness, (ViewGroup) findViewById(R.id.layout_dialog));  

        popDialog.setTitle("Set brightness");
        popDialog.setView(Viewlayout);

    brightbar = (SeekBar) findViewById(R.id.brightbar);
    txtPerc = (TextView) findViewById(R.id.txtPercentage);
    cResolver = getContentResolver();
    window = getWindow();
    brightbar.setMax(255);
    brightbar.setKeyProgressIncrement(1);

    brightbar = (SeekBar) findViewById(R.id.brightbar);
    txtPerc = (TextView) findViewById(R.id.txtPercentage);
    cResolver = getContentResolver();
    window = getWindow();
    brightbar.setMax(255);
    brightbar.setKeyProgressIncrement(1);

    try
    {
        brightness = Settings.System.getInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS);
        float perc = (brightness /(float)255)*100;
        txtPerc.setText((int)perc +" %");
    }
    catch (SettingNotFoundException e)
    {
        Log.e("Error", "Cannot access system brightness");
        e.printStackTrace();
    }

    brightbar.setProgress(brightness);
    brightbar.setOnSeekBarChangeListener(new OnSeekBarChangeListener()
    {
        public void onStopTrackingTouch(SeekBar seekBar)
        {
            Settings.System.putInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS, brightness);
            LayoutParams layoutpars = window.getAttributes();
            layoutpars.screenBrightness = brightness / (float)255;
            window.setAttributes(layoutpars);
        }

        public void onStartTrackingTouch(SeekBar seekBar)
        {

        }

        public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser)
        {


                brightness = progress;

                float perc = (brightness /(float)255)*100;
                txtPerc.setText((int)perc +" %");
        }
    });     

    popDialog.setNeutralButton("Close",
            new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    dialog.dismiss();
                }

            });

    popDialog.create();
    popDialog.show();

}
}

在另一个类 PreferenceActivity 中，我有一个偏好，即“亮度”。我想点击它会打开首选项对话框，然后我输入这段代码。

Preference brigh;
brigh = (Preference) this.findPreference("brightness_pref");

brigh.setOnPreferenceClickListener( new OnPreferenceClickListener() {
    public boolean onPreferenceClick(Preference preference) {

    Brightness brightness = new Brightness();
        brightness.ShowDialog();

        return true;

    }
});

但是当我运行应用程序并单击首选项时，崩溃了。这是日志猫

11-10 18:23:34.955：E/AndroidRuntime(945)：致命异常：主 11-10 18：23：34.955：E/AndroidRuntime（945）：java.lang.NullPointerException 11-10 18:23:34.955: E/AndroidRuntime(945): 在 android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:146) 11-10 18:23:34.955: E/AndroidRuntime(945): 在 android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:103) 11-10 18:23:34.955: E/AndroidRuntime(945): 在 android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:143) 11-10 18：23：34.955：E/AndroidRuntime（945）：在 android.app.AlertDialog$Builder.(AlertDialog.java:360) 11-10 18：23：34.955：E/AndroidRuntime（945）：在 com.simonedev.androtools.Brightness.ShowDialog(Brightness.java:39) 11-10 18:23:34.955: E/AndroidRuntime(945): 在 com.simonedev.androtools.Impostazioni$1.onPreferenceClick(Settings.java:48) 11-10 18:23:34.955: E/AndroidRuntime(945): 在 android.preference.Preference.performClick(Preference.java:952) 11-10 18：23：34.955：E/AndroidRuntime（945）：在 android.preference.PreferenceScreen.onItemClick(PreferenceScreen.java:215) 11-10 18:23:34.955: E/AndroidRuntime(945): 在 android.widget.AdapterView.performItemClick(AdapterView.java:297) 11-10 18:23:34.955: E/AndroidRuntime(945): 在 android.widget.AbsListView.performItemClick(AbsListView.java:1100) 11-10 18:23:34.955: E/AndroidRuntime(945): 在 android.widget.AbsListView$PerformClick.run(AbsListView.java:2788) 11-10 18:23:34.955: E/AndroidRuntime(945): 在 android.widget.AbsListView$1.run(AbsListView.java:3463) 11-10 18：23：34.955：E/AndroidRuntime（945）：在 android.os.Handler.handleCallback(Handler.java:730) 11-10 18：23：34.955：E/AndroidRuntime（945）：在 android.os.Handler.dispatchMessage(Handler.java:92) 11-10 18：23：34.955：E/AndroidRuntime（945）：在 android.os.Looper.loop(Looper.java:137) 11-10 18:23:34.955: E/AndroidRuntime(945)：在 android.app.ActivityThread.main(ActivityThread.java:5289) 11-10 18：23：34.955：E/AndroidRuntime（945）：在 java.lang.reflect.Method.invokeNative(Native Method) 11-10 18：23：34.955：E/AndroidRuntime（945）：在 java.lang.reflect.Method.invoke(Method.java:525) 11-10 18:23:34.955: E/AndroidRuntime(945)：在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739) 11-10 18:23:34.955: E/AndroidRuntime(945): 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555) 11-10 18：23：34.955：E/AndroidRuntime（945）：在 dalvik.system.NativeStart.main(Native Method)

我不明白如何解决。你能帮帮我吗？

Answer 1

编辑 因为你不是有意图地开始活动。如果您只想显示 AlertDialog，您可以在 PreferenceActivity 中使用。

final AlertDialog.Builder popDialog = new AlertDialog.Builder(getApplicationContext());