Android 使用公共静态字段在活动之间共享数据
我正在尝试实现一个应用程序，它允许使用3种不同的共同例程活动搜索二叉树。这些活动可以选择以任何顺序运行，并且每个活动都应该能够访问有关最近访问的节点的共享数据，以便它们可以继续搜索树 用文字解释这一点有点复杂，所以我想我应该在这里粘贴部分代码。以下是我的一项共同日常活动的代码（其他两项基本相同）： 主要活动的代码：Android 使用公共静态字段在活动之间共享数据,android,static,nullpointerexception,shared,public,Android,Static,Nullpointerexception,Shared,Public,我正在尝试实现一个应用程序，它允许使用3种不同的共同例程活动搜索二叉树。这些活动可以选择以任何顺序运行，并且每个活动都应该能够访问有关最近访问的节点的共享数据，以便它们可以继续搜索树 用文字解释这一点有点复杂，所以我想我应该在这里粘贴部分代码。以下是我的一项共同日常活动的代码（其他两项基本相同）： 主要活动的代码： public class SearchSharedTreeActivity extends Activity implements OnClickListener { pri
public class SearchSharedTreeActivity extends Activity implements OnClickListener {
private EditText target = null;
private EditText corout1 = null;
private EditText corout2 = null;
private EditText corout3 = null;
private Button target_btn = null;
private Button corout1_btn = null;
private Button corout2_btn = null;
private Button corout3_btn = null;
private static final int COROUT_ONE_REQCODE = 1;
private static final int COROUT_TWO_REQCODE = 2;
private static final int COROUT_THREE_REQCODE = 3;
public static BinaryTree tree = null;
public static Vector nodeList = null;
public static BinaryTree.Node current = null;
public static Comparable item = null;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tree = new BinaryTree();
Comparable[] values = {20, 10, 30, 5, 17, 25, 40, 11, 35, 55};
tree.insert(values);
target = (EditText) findViewById(R.id.target_input);
corout1 = (EditText) findViewById(R.id.co1_output);
corout2 = (EditText) findViewById(R.id.co2_output);
corout3 = (EditText) findViewById(R.id.co3_output);
target_btn = (Button) findViewById(R.id.target_btn);
corout1_btn = (Button) findViewById(R.id.co1_btn);
corout2_btn = (Button) findViewById(R.id.co2_btn);
corout3_btn = (Button) findViewById(R.id.co3_btn);
target_btn.setOnClickListener(this);
corout1_btn.setOnClickListener(this);
corout2_btn.setOnClickListener(this);
corout3_btn.setOnClickListener(this);
}
public void onClick(View view){
Button btn = (Button) view;
int id = btn.getId();
if (id == R.id.target_btn){
item = target.getText().toString();
try{
Integer.parseInt((String) item);
target.setText("Target is " + item);
}catch (Exception e){
target.setText("");
corout1.setText("");
corout2.setText("");
corout3.setText("");
}
}
else if (id == R.id.co1_btn){
Intent i1 = new Intent(this, CoRoutineOne.class);
startActivityForResult(i1, COROUT_ONE_REQCODE);
}
else if (id == R.id.co2_btn){
Intent i2 = new Intent(this, CoRoutineTwo.class);
startActivityForResult(i2, COROUT_TWO_REQCODE);
}
else if (id == R.id.co3_btn){
Intent i3 = new Intent(this, CoRoutineThree.class);
startActivityForResult(i3, COROUT_THREE_REQCODE);
}
}
public void onActivityResult(int requestCode, int resultCode, Intent data){
if (requestCode == COROUT_ONE_REQCODE){
if (resultCode == Activity.RESULT_OK){
if (item.equals(current.value))
corout1.setText("Found " + current.value);
else if (current == null)
corout1.setText("Not found");
else
corout1.setText("Reached " + current.value);
}
else
corout1.setText("Problem finding target");
}
else if (requestCode == COROUT_TWO_REQCODE){
if (resultCode == Activity.RESULT_OK){
if (item.equals(current.value))
corout2.setText("Found " + current.value);
else if (current == null)
corout2.setText("Not found");
else
corout2.setText("Reached " + current.value);
}
else
corout2.setText("Problem finding target");
}
else if (requestCode == COROUT_THREE_REQCODE){
if (resultCode == Activity.RESULT_OK){
if (item.equals(current.value))
corout3.setText("Found " + current.value);
else if (current == null)
corout3.setText("Not found");
else
corout3.setText("Reached " + current.value);
}
else
corout3.setText("Problem finding target");
}
}
}
树节点列表当前项公共静态NullPointerExceptionRESULT\u取消
请帮我指出问题所在。谢谢你的建议。也许我是瞎子。。。但是我没有看到节点列表
（或其他静态
字段）设置为除null
之外的任何其他字段。这些是在哪里定义的？我只在协作例程活动中的列表中添加一个新节点，当它们开始搜索树并访问第一个节点时。树
是在主活动的onCreate
方法中定义的，而项
是在用户单击目标按钮时设置的（因此在onClick
方法中定义）。但是如果SearchSharedTreeActivity.nodeList
为null
，则不能。向其添加。您必须首先将其声明为新向量（…）
。
public class SearchSharedTreeActivity extends Activity implements OnClickListener {
private EditText target = null;
private EditText corout1 = null;
private EditText corout2 = null;
private EditText corout3 = null;
private Button target_btn = null;
private Button corout1_btn = null;
private Button corout2_btn = null;
private Button corout3_btn = null;
private static final int COROUT_ONE_REQCODE = 1;
private static final int COROUT_TWO_REQCODE = 2;
private static final int COROUT_THREE_REQCODE = 3;
public static BinaryTree tree = null;
public static Vector nodeList = null;
public static BinaryTree.Node current = null;
public static Comparable item = null;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tree = new BinaryTree();
Comparable[] values = {20, 10, 30, 5, 17, 25, 40, 11, 35, 55};
tree.insert(values);
target = (EditText) findViewById(R.id.target_input);
corout1 = (EditText) findViewById(R.id.co1_output);
corout2 = (EditText) findViewById(R.id.co2_output);
corout3 = (EditText) findViewById(R.id.co3_output);
target_btn = (Button) findViewById(R.id.target_btn);
corout1_btn = (Button) findViewById(R.id.co1_btn);
corout2_btn = (Button) findViewById(R.id.co2_btn);
corout3_btn = (Button) findViewById(R.id.co3_btn);
target_btn.setOnClickListener(this);
corout1_btn.setOnClickListener(this);
corout2_btn.setOnClickListener(this);
corout3_btn.setOnClickListener(this);
}
public void onClick(View view){
Button btn = (Button) view;
int id = btn.getId();
if (id == R.id.target_btn){
item = target.getText().toString();
try{
Integer.parseInt((String) item);
target.setText("Target is " + item);
}catch (Exception e){
target.setText("");
corout1.setText("");
corout2.setText("");
corout3.setText("");
}
}
else if (id == R.id.co1_btn){
Intent i1 = new Intent(this, CoRoutineOne.class);
startActivityForResult(i1, COROUT_ONE_REQCODE);
}
else if (id == R.id.co2_btn){
Intent i2 = new Intent(this, CoRoutineTwo.class);
startActivityForResult(i2, COROUT_TWO_REQCODE);
}
else if (id == R.id.co3_btn){
Intent i3 = new Intent(this, CoRoutineThree.class);
startActivityForResult(i3, COROUT_THREE_REQCODE);
}
}
public void onActivityResult(int requestCode, int resultCode, Intent data){
if (requestCode == COROUT_ONE_REQCODE){
if (resultCode == Activity.RESULT_OK){
if (item.equals(current.value))
corout1.setText("Found " + current.value);
else if (current == null)
corout1.setText("Not found");
else
corout1.setText("Reached " + current.value);
}
else
corout1.setText("Problem finding target");
}
else if (requestCode == COROUT_TWO_REQCODE){
if (resultCode == Activity.RESULT_OK){
if (item.equals(current.value))
corout2.setText("Found " + current.value);
else if (current == null)
corout2.setText("Not found");
else
corout2.setText("Reached " + current.value);
}
else
corout2.setText("Problem finding target");
}
else if (requestCode == COROUT_THREE_REQCODE){
if (resultCode == Activity.RESULT_OK){
if (item.equals(current.value))
corout3.setText("Found " + current.value);
else if (current == null)
corout3.setText("Not found");
else
corout3.setText("Reached " + current.value);
}
else
corout3.setText("Problem finding target");
}
}
}