[英]Android setOnClickListener not working
在android中添加按鈕動作后,Activity.java應用程序不幸關閉。 請幫助解決。 我在這里缺少什么代碼????
public class MainActivity extends ActionBarActivity {
int counter;
Button add, sub;
TextView display;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
counter = 0;
add = (Button) findViewById(R.id.bAdd);
sub = (Button) findViewById(R.id.bSub);
display = (TextView) findViewById(R.id.textDisp);
add.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// Perform action on click
counter++;
}
});
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}
}
看來您是在fragment_main.xml而不是activity_main.xml中建立視圖的。
首次創建新的android項目時,您會擁有以下這些文件,這些文件會自動創建並打開:
然后,當您開始時,您可以在fragment_main.xml
文件中添加視圖(例如:TextView) 。 而您嘗試在Activity
使用此視圖進行一個基本的事件,如下所示:
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); // Using layout activity_main.xml
// You try to set a simple text on the view (TextView) previously added
TextView text = (TextView) findViewById(R.id.textView1);
text.setText("Simple Text"); // And you get an error here!
/*
* You do an fragment transaction to add PlaceholderFragment Fragment
* on screen - this below snippnet is automatically created.
*/
if(savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
}
您無法運行您的應用程序,或者有時您只有白屏,因為您嘗試調用/顯示的視圖布局錯誤。
解決方案: 將onCreateView方法中的所有內容移到Fragment類中。 調用視圖並在相關片段而不是父活動中執行某些操作 。
例如,對於您的情況:
public static class PlaceholderFragment extends Fragment {
int counter;
Button add, sub;
TextView display;
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
counter = 0;
// Don't forget to attach your view to the inflated view as "rootView.findViewById()"
add = (Button) rootView.findViewById(R.id.bAdd);
sub = (Button) rootView.findViewById(R.id.bSub);
display = (TextView) rootView.findViewById(R.id.textDisp);
add.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// Perform action on click
counter++;
}
});
return rootView;
}
}
我得到了解決方案,我也進行了測試
問題不只是將代碼移入
但我在移動代碼后也必須使用以下內容
add = (Button) rootView.findViewById (R.id.bAdd);
sub = (Button) rootView.findViewById(R.id.bSub);
display = (TextView) rootView.findViewById(R.id.tvDisplay);
代替以下
add = (Button) findViewById (R.id.bAdd);
sub = (Button) findViewById(R.id.bSub);
display = (TextView) findViewById(R.id.tvDisplay);
我希望任何機構在這里發表評論以解釋這種行為
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