Android---重新認識view--Visiable\Invisiable\Gone屬性

------ 對於一切模糊的事情，我總要親自試一試，找到最清晰的答案，並記錄下來

------ View的3個屬性Visiable\Invisiable\Gone官方說明

 case R.id.btn_show:
                /*this view is visible.*/
                mListView.setVisibility(View.VISIBLE);
                break;
            case R.id.btn_dismiss_gone:
                 /*this view is invisible, and it dosen't take any space*/
                mListView.setVisibility(View.GONE);
                break;
            case R.id.btn_dismiss_invisiable:
                /*this view is invisible, and it still takes up space*/
                mListView.setVisibility(View.INVISIBLE);
                break;

---- layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#3000"
    android:gravity="center"
    android:orientation="vertical">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/btn_show"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="show" />

        <Button
            android:id="@+id/btn_dismiss_gone"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="dismiss_gone" />

        <Button
            android:id="@+id/btn_dismiss_invisiable"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="dismiss_invisiable" />
    </LinearLayout>

    <com.helin.loadinglayout.LoadingLayout
        android:id="@+id/loading_layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <ListView
            android:id="@+id/list_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:dividerHeight="2dp"></ListView>

    </com.helin.loadinglayout.LoadingLayout>

</LinearLayout>

------- code

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_material_progressbar);
        initView();
        initData();
        initListenter();
    }

    private void initView() {
        mListView = (ListView) findViewById(R.id.list_view);
        btnDismiss = (Button) findViewById(R.id.btn_dismiss_gone);
        btnShow = (Button) findViewById(R.id.btn_show);
        btnInvisable = (Button) findViewById(R.id.btn_dismiss_invisiable);
    }


    private void initData() {
        ArrayAdapter<String> stringArrayAdapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1);
        setStrings(stringArrayAdapter);
        mListView.setAdapter(stringArrayAdapter);
    }

    private void initListenter() {
        btnShow.setOnClickListener(this);
        btnDismiss.setOnClickListener(this);
        btnInvisable.setOnClickListener(this);
    }

    @NonNull
    private void setStrings(ArrayAdapter<String> arrayAdapter) {
        for (int i = 0; i < 30; i++) {
            arrayAdapter.add("item" + i);
        }
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn_show:
                /*this view is visible.*/
                mListView.setVisibility(View.VISIBLE);
                break;
            case R.id.btn_dismiss_gone:
                 /*this view is invisible, and it dosen't take any space*/
                mListView.setVisibility(View.GONE);
                break;
            case R.id.btn_dismiss_invisiable:
                /*this view is invisible, and it still takes up space*/
                mListView.setVisibility(View.INVISIBLE);
                break;
            default:
                break;
        }
    }

---- - gif

-------- 結論

View設置爲InVisiable\Gone，其實例依然存在，其引用並不會發生NullPoniterException