Question

我似乎在应用程序崩溃：

parent.findViewById（R.id.a_1）.setVisibility（View.VISIBLE）;

不确定我做错了什么

代码在

之下

layouttext.java

    public class layouttest extends Activity {
 private Spinner solvefor; 
 private ArrayAdapter<CharSequence> featuresAdapter; 
 private List<CharSequence> featuresList; 

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        featuresList = new ArrayList<CharSequence>(); 
        featuresAdapter = new ArrayAdapter<CharSequence>(this, android.R.layout.simple_spinner_item, featuresList); 
        featuresAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 
        solvefor = ((Spinner) layouttest.this.findViewById(R.id.solvefor)); 
        solvefor.setAdapter(featuresAdapter); 
        featuresAdapter.add("Velocity"); 
        featuresAdapter.add("Time"); 
        featuresAdapter.add("Distance"); 
        solvefor.setOnItemSelectedListener(new MyOnItemSelectedListener());
    }
}

MyOnItemSelectedListener.java 包android.example.layouttest;

import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.Toast;

public class MyOnItemSelectedListener implements OnItemSelectedListener {
 private static final int SPINNER_OPTION_FIRST = 0; 
    private static final int SPINNER_OPTION_SECOND = 1;
 public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
   switch(pos) { 
         case SPINNER_OPTION_FIRST: { 
          Toast.makeText(parent.getContext(), "0", Toast.LENGTH_LONG).show();
          break;
         } 
         case SPINNER_OPTION_SECOND: { 
          Toast.makeText(parent.getContext(), "1", Toast.LENGTH_LONG).show();
          parent.findViewById(R.id.a_1).setVisibility(View.VISIBLE);
          parent.findViewById(R.id.a_2).setVisibility(View.VISIBLE);
          break;
         } 
  }  
 }   
 public void onNothingSelected(AdapterView<?> parent) {      
   // Do nothing.    
   }
}

Answer 1

请记住View#findViewById从您调用它的视图开始搜索并下降到其子级。如果包含您要查找的ID的视图不是视图本身或该视图的后代，则搜索将失败，findViewById将返回null。

正如Falmarri建议的那样，您可能不希望在{1}}上呼叫findViewById。（您可能也不想在parent从那里调用它。）

您希望在视图层次结构中找到view？

的位置

使用setVisibility时出现android崩溃（View.VISIBLE）

1 个答案: