Android PopupWindow用法（一）

Section1

代码如下

public class MainActivity extends AppCompatActivity {    private LinearLayout ll_main;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        ll_main = (LinearLayout) findViewById(R.id.ll_main);        PopupWindow popupWindow = new PopupWindow(this);        popupWindow.setContentView(View.inflate(this,R.layout.layout_popup,null));        findViewById(android.R.id.content);        popupWindow.showAsDropDown(ll_main);    }}

  Caused by: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?

Section2  报错了，修改代码如下

private LinearLayout ll_main;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    ll_main = (LinearLayout) findViewById(R.id.ll_main);}@Overridepublic void onWindowFocusChanged(boolean hasFocus) {    super.onWindowFocusChanged(hasFocus);    PopupWindow popupWindow = new PopupWindow(this);    popupWindow.setContentView(View.inflate(this,R.layout.layout_popup,null));    findViewById(android.R.id.content);    popupWindow.showAsDropDown(ll_main);}

这次是不报错了，但是popupwindow还是没有出来。

Section3

难道是因为inflate的时候没有指定parent?

public class MainActivity extends AppCompatActivity {    private LinearLayout ll_main;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        ll_main = (LinearLayout) findViewById(R.id.ll_main);    }    @Override    public void onWindowFocusChanged(boolean hasFocus) {        super.onWindowFocusChanged(hasFocus);        PopupWindow popupWindow = new PopupWindow(this);        popupWindow.setContentView(View.inflate(this, R.layout.layout_popup, ll_main));        findViewById(android.R.id.content);        popupWindow.showAsDropDown(ll_main);    }}

 java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
                                         

更不对，因为这个view并不是ll_main的child，ll_main作为parent显然是错误的

Section4

到底是什么原因，其实原因很简单，因为popWindow new 的时候需要指定宽高，

我们继续修改代码

public class MainActivity extends AppCompatActivity {    private LinearLayout ll_main;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        ll_main = (LinearLayout) findViewById(R.id.ll_main);    }    @Override    public void onWindowFocusChanged(boolean hasFocus) {        super.onWindowFocusChanged(hasFocus);        PopupWindow popupWindow = new PopupWindow(100,100);        popupWindow.setContentView(View.inflate(this,R.layout.layout_popup,null));        findViewById(android.R.id.content);        popupWindow.showAsDropDown(ll_main);    }}

这次终于出来了。