Android---重新认识view--Visiable\Invisiable\Gone属性

------ 对于一切模糊的事情，我总要亲自试一试，找到最清晰的答案，并记录下来

------ View的3个属性Visiable\Invisiable\Gone官方说明

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



-------- 结论

View设置为InVisiable\Gone，其实例依然存在，其引用并不会发生NullPoniterException