Android ImageButton OnClick 給出空指針異常

Question

我從一個菜單選項中調用一個彈出對話框，上面寫着登錄：然后將 Twitter 和 Google 徽標顯示為 2 個圖像按鈕。

AlertDialog.Builder alertadd = new AlertDialog.Builder(
            SummaryActivity.this);
    LayoutInflater factory = LayoutInflater.from(SummaryActivity.this);
    final View view = factory.inflate(R.layout.social_network_selection, null);
    alertadd.setView(view);

它膨脹包含 2 個圖像按鈕的視圖。

當我添加代碼時

    googleButton2 = (ImageButton)findViewById(R.id.googleButton);
    twitterButton2 = (ImageButton)findViewById(R.id.twitterButton);

一切正常，但是當我添加

googleButton2.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {

           Toast.makeText(MyAndroidAppActivity.this,
            "googleButton2 is clicked!", Toast.LENGTH_SHORT).show();

        }

    });

它因空指針而崩潰。 不是當我點擊按鈕時，而是第二次我調用包含 ImageButtons 的 AlertDialog

如何將偵聽器添加到 AlertDialog 膨脹視圖上的圖像按鈕？

邏輯貓

java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
        at android.support.v7.internal.view.SupportMenuInflater$InflatedOnMenuItemClickListener.onMenuItemClick(SupportMenuInflater.java:259)
        at android.support.v7.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:149)
        at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:958)
        at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:948)
        at android.support.v7.internal.view.menu.MenuPopupHelper.onItemClick(MenuPopupHelper.java:191)

Answer 1

問題出在這些行中，

googleButton2 = (ImageButton)findViewById(R.id.googleButton);
twitterButton2 = (ImageButton)findViewById(R.id.twitterButton);

findViewById(int) 方法在上下文布局中找不到 id 因此它返回空值

解決方案

您應該必須使用 findViewById 方法來查找由布局上下文膨脹的視圖。

這是您的任務所需的解決方案，

 AlertDialog.Builder alertadd = new AlertDialog.Builder(
                SummaryActivity.this);
    LayoutInflater factory = LayoutInflater.from(SummaryActivity.this);
    final View view = factory.inflate(R.layout.social_network_selection, null);
    alertadd.setView(view);
    googleButton2 = (ImageButton) view.findViewById(R.id.googleButton);
    twitterButton2 = (ImageButton) view.findViewById(R.id.twitterButton);

    googleButton2.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {

               Toast.makeText(MyAndroidAppActivity.this,
                "googleButton2 is clicked!", Toast.LENGTH_SHORT).show();

            }

        });

Answer 2

使用 View 視圖的名稱調用 imagebutton，您的 onClick 使用 getBaseContext()

 AlertDialog.Builder alertadd = new AlertDialog.Builder(
                SummaryActivity.this);
        LayoutInflater factory = LayoutInflater.from(SummaryActivity.this);
        final View view = factory.inflate(R.layout.social_network_selection, null);
    ImageButton googleButton2 = (ImageButton)view.findViewById(R.id.googleButton);
        ImageButton twitterButton2 = (ImageButton)view.findViewById(R.id.twitterButton);

    googleButton2.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {

               Toast.makeText(getBaseContext(),
                "googleButton2 is clicked!", Toast.LENGTH_SHORT).show();

            }

        });
        alertadd.setView(view);