记事本APP崩溃。。。（新手）

青鸟丶 2017-07-20 11:19:45

用的android studio
就是两个Activity之间的跳转，
点击新建记事就崩溃了
错误信息:E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.administrator.jishiben, PID: 5078
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.administrator.jishiben/com.example.administrator.jishiben.Main2Activity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

活动1部分代码：



public class MainActivity extends Activity implements  OnItemClickListener, OnItemLongClickListener {

        private Context mContext;

        private ListView listview;

        private SimpleAdapter simp_adapter;

        private List<Map<String, Object>> dataList;

        private Button addNote;

        private TextView tv_content;

        private NotesDB DB;

        private SQLiteDatabase dbread;



        @Override

        protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);

            setContentView(R.layout.activity_main);

            tv_content = (TextView) findViewById(R.id.tv_content);

            listview = (ListView) findViewById(R.id.listview);

            dataList = new ArrayList<Map<String, Object>>();



            addNote = (Button) findViewById(R.id.btn_editnote);

            mContext = this;

            addNote.setOnClickListener(new OnClickListener() {



                @Override

                public void onClick(View arg0) {

                    Main2Activity.ENTER_STATE = 0;

                    Intent intent = new Intent(mContext, Main2Activity.class);

                    Bundle bundle = new Bundle();

                    bundle.putString("info", "");

                    intent.putExtras(bundle);

                    startActivityForResult(intent, 1);

                }

            });

            DB = new NotesDB(this);

            dbread = DB.getReadableDatabase();

            // 清空数据库中表的内容

            //dbread.execSQL("delete from note");

            RefreshNotesList();

            listview.setOnItemClickListener(this);

            listview.setOnItemLongClickListener(this);



        }

    public void RefreshNotesList() {



        int size = dataList.size();

        if (size > 0) {

            dataList.removeAll(dataList);

            simp_adapter.notifyDataSetChanged();

            listview.setAdapter(simp_adapter);

        }

        simp_adapter = new SimpleAdapter(this, getData(), R.layout.jishi,

                new String[] { "tv_content", "tv_date" }, new int[] {

                R.id.tv_content, R.id.tv_date });

        listview.setAdapter(simp_adapter);

    }



    private List<Map<String, Object>> getData() {



        Cursor cursor = dbread.query("note", null, "content!=\"\"", null, null,

                null, null);



        while (cursor.moveToNext()) {

            String name = cursor.getString(cursor.getColumnIndex("content"));

            String date = cursor.getString(cursor.getColumnIndex("date"));

            Map<String, Object> map = new HashMap<String, Object>();

            map.put("tv_content", name);

            map.put("tv_date", date);

            dataList.add(map);

        }

        cursor.close();

        return dataList;



    }



    public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {

        Main2Activity.ENTER_STATE = 1;

        // Log.d("arg2", arg2 + "");

        // TextView

        // content=(TextView)listview.getChildAt(arg2).findViewById(R.id.tv_content);

        // String content1=content.toString();

        String content = listview.getItemAtPosition(arg2) + "";

        String content1 = content.substring(content.indexOf("=") + 1,

                content.indexOf(","));

        Log.d("CONTENT", content1);

        Cursor c = dbread.query("note", null,

                "content=" + "'" + content1 + "'", null, null, null, null);

        while (c.moveToNext()) {

            String No = c.getString(c.getColumnIndex("_id"));

            Log.d("TEXT", No);

            // Intent intent = new Intent(mContext, noteEdit.class);

            // intent.putExtra("data", text);

            // setResult(4, intent);

            // // intent.putExtra("data",text);

            // startActivityForResult(intent, 3);

            Intent myIntent = new Intent();

            Bundle bundle = new Bundle();

            bundle.putString("info", content1);

            Main2Activity.id = Integer.parseInt(No);

            myIntent.putExtras(bundle);

            myIntent.setClass(MainActivity.this,Main2Activity.class);

            startActivityForResult(myIntent, 1);

        }

    }

    protected void onActivityResult(int requestCode, int resultCode, Intent data) {

        // TODO Auto-generated method stub

        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == 1 && resultCode == 2) {

            RefreshNotesList();

        }

    }

}

活动2代码：

package com.example.administrator.jishiben;



import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import java.text.SimpleDateFormat;

import java.util.Date;



import android.app.Activity;

import android.content.Context;

import android.content.Intent;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteStatement;

import android.os.Bundle;

import android.util.Log;

import android.view.View;

import android.view.View.OnClickListener;

import android.view.Window;

import android.view.WindowManager;

import android.view.inputmethod.InputMethodManager;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;



public class Main2Activity extends Activity {

    private TextView tv_date;

    private EditText et_content;

    private Button btn_ok;

    private Button btn_cancel;

    private NotesDB DB;

    private SQLiteDatabase dbread;

    public static int ENTER_STATE = 0;

    public static String last_content;

    public static int id;



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        // TODO Auto-generated method stub

        super.onCreate(savedInstanceState);

        // 设置无标题

        requestWindowFeature(Window.FEATURE_NO_TITLE);

        setContentView(R.layout.activity_main2);



        tv_date = (TextView) findViewById(R.id.tv_date);

        Date date = new Date();

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm");

        String dateString = sdf.format(date);

        tv_date.setText(dateString);



        et_content = (EditText) findViewById(R.id.et_content);

        // 设置软键盘自动弹出

        getWindow().setSoftInputMode(

                WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_VISIBLE);



        DB = new NotesDB(this);

        dbread = DB.getReadableDatabase();



        Bundle myBundle = this.getIntent().getExtras();

        last_content = myBundle.getString("info");

        Log.d("LAST_CONTENT", last_content);

        et_content.setText(last_content);

        // 确认按钮的点击事件

        btn_ok = (Button) findViewById(R.id.btn_ok);

        btn_ok.setOnClickListener(new OnClickListener() {

            public void onClick(View arg0) {

                // 获取日志内容

                String content = et_content.getText().toString();

                Log.d("LOG1", content);

                // 获取写日志时间

                Date date = new Date();

                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

                String dateNum = sdf.format(date);

                String sql;

                String sql_count = "SELECT COUNT(*) FROM note";

                SQLiteStatement statement = dbread.compileStatement(sql_count);

                long count = statement.simpleQueryForLong();

                Log.d("COUNT", count + "");

                Log.d("ENTER_STATE", ENTER_STATE + "");

                // 添加一个新的日志

                if (ENTER_STATE == 0) {

                    if (!content.equals("")) {

                        sql = "insert into " + NotesDB.TABLE_NAME_NOTES

                                + " values(" + count + "," + "'" + content

                                + "'" + "," + "'" + dateNum + "')";

                        Log.d("LOG", sql);

                        dbread.execSQL(sql);

                    }

                }

                // 查看并修改一个已有的日志

                else {

                    Log.d("执行命令", "执行了该函数");

                    String updatesql = "update note set content='"

                            + content + "' where _id=" + id;

                    dbread.execSQL(updatesql);

                    // et_content.setText(last_content);

                }

                Intent data = new Intent();

                setResult(2, data);

                finish();

            }

        });

        btn_cancel = (Button) findViewById(R.id.btn_cancel);

        btn_cancel.setOnClickListener(new OnClickListener() {

            public void onClick(View arg0) {

                finish();

            }

        });

    }



    @Override

    protected void onActivityResult(int requestCode, int resultCode, Intent data) {

        // TODO Auto-generated method stub

        super.onActivityResult(requestCode, resultCode, data);

        // if (requestCode == 3 && resultCode == 4) {

        // last_content=data.getStringExtra("data");

        // Log.d("LAST_STRAING", last_content+"gvg");

        // }

    }

}