在交换机案例中获取Toasts的空对象引用错误

无论我做什么,我都会遇到错误,比如null object reference当我尝试在开关盒内调用吐司时.switch方法所在的类扩展了FragmentActivity

我试图扩展Fragment/v4.和没有succses的活动.我也尝试将getContext, getBaseContext, getAppliction();, getApplication().getBaseContext etcas上下文传递给toast而没有succses

如果我在我的MainActivity中创建一个公共Toast对象并像这样使用它MainActivity.copyToast.show();可以工作,但这个解决方案看起来并不好看.

我希望将它保存在一行中: Toast.makeText(this.getApplicationContext(), "Copied to clipboard.", Toast.LENGTH_SHORT).show();

全班:

public class CustomTextSelectionMenu extends Fragment implements android.view.ActionMode.Callback {



@Override
public boolean onCreateActionMode(android.view.ActionMode mode, Menu menu) {
    MenuInflater inflater = mode.getMenuInflater();
    inflater.inflate(R.menu.menu_main, menu);
    menu.removeItem(android.R.id.selectAll);
    menu.removeItem(android.R.id.paste);



    return true;
}

@Override
public boolean onPrepareActionMode(android.view.ActionMode mode, Menu menu) {
    return false;
}

@Override
public boolean onActionItemClicked(android.view.ActionMode mode, MenuItem item) {

    int selectionStart = editText.getSelectionStart();
    int selectionEnd = editText.getSelectionEnd();

    if (selectionEnd > selectionStart) {
        Spannable str = editText.getText();
        boolean exists = false;
        StyleSpan[] styleSpans;

        switch (item.getItemId()) {


            //--------------------COPY----------------------------
            case android.R.id.copy:
                CharSequence charSequence =   editText.getText().subSequence(selectionStart, selectionEnd);
                ClipData clip = ClipData.newPlainText("simple text", charSequence);
                MainActivity.clipboard.setPrimaryClip(clip);



                Toast.makeText(getActivity().getApplicationContext(),  "Copied to clipboard.", Toast.LENGTH_SHORT).show();
                //MainActivity.copyToast.show();
                break;

            //--------------------BOLD----------------------------
            case R.id.bold:

                styleSpans = str.getSpans(selectionStart, selectionEnd, StyleSpan.class);

                // If the selected text-part already has BOLD style on it, then
                // we need to disable it
                for (int i = 0; i < styleSpans.length; i++) {
                    if (styleSpans[i].getStyle() == android.graphics.Typeface.BOLD) {
                        str.removeSpan(styleSpans[i]);
                        exists = true;
                    }
                }

                // Else we set BOLD style on it
                if (!exists) {
                    str.setSpan(new StyleSpan(android.graphics.Typeface.BOLD), selectionStart, selectionEnd,
                            Spannable.SPAN_EXCLUSIVE_INCLUSIVE);
                }

                editText.setSelection(selectionStart, selectionEnd);



                break;     

        }
    }
    return true;

}


@Override
public void onDestroyActionMode(android.view.ActionMode mode) {


}

}

堆栈跟踪:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:110)
at org.m.muddzboy.QuoteCreator.CustomTextSelectionMenu.onActionItemClicked(CustomTextSelectionMenu.java:182)
at android.widget.Editor$SelectionActionModeCallback.onActionItemClicked(Editor.java:3228)

第182行指出:

Toast.makeText(this.getApplicationContext(), "Copied to clipboard.", Toast.LENGTH_SHORT).show();

吐司方法可能会导致许多问题,我们必须解决它,这就是为什么我回答这个问题.

第一个上下文称为null,并在您的情况下崩溃您的应用程序.

如何解决它:在create方法上保持对上下文的引用

private Context mContext;

 @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
     mContext = getActivity()
}

第二次显示吐司时可能会破坏片段如何确保它不会崩溃

public void showToast(String msg) {
        if (YOR_FRAGMENT.this.isVisible() && msg != null & mContext != null)
            Toast.makeText(mContext, msg, Toast.LENGTH_LONG).show();
    }

这将使你远离吐司崩溃

希望这个帮助