[英]How to clear the hash map<string,string> values?
I want to clear all the hash map values before the values are assigned to hash map from db.For eg., hashmap<string,string> demo
is my hashmap in that i have added the following values from db.The result response from hashmap is {A=1, B=2, C=3, D=4, E=5}
.After view loads I want to insert this in above hashmap {A=test, B=demo, C=sample, D=empty, E=null}
.For this how can I clear the first values before inserting the second set of values.And also I have tried by using demo.clear()
it is not working.How can I clear the 1st list of values before adding the 2nd one.Suggest some solutions to solve the problem. 我希望清除所有哈希映射值,然后将值从db分配给哈希映射。例如, hashmap<string,string> demo
是我的hashmap,因为我已经从db添加了以下值。来自hashmap的结果响应是{A=1, B=2, C=3, D=4, E=5}
。视图加载后我想在上面的hashmap中插入它{A=test, B=demo, C=sample, D=empty, E=null}
。为此,如何在插入第二组值之前清除第一个值。我也尝试使用demo.clear()
它不起作用。如何清除第一个值列表之前添加第二个。提出一些解决方案来解决问题。
This is the code to retrieve data from db. 这是从db检索数据的代码。
public HashMap<String, String> getdata() {
try {
HashMap<String, String> map = new HashMap<String, String>();
Log.e("getdata", "Started");
String selectQuery = "SELECT * FROM tablename";
SQLiteDatabase database = this.getWritableDatabase();
Cursor cursor = database.rawQuery(selectQuery, null);
if (cursor.moveToFirst()) {
do {
map.put(cursor.getString(cursor.getColumnIndex("colmn1")),
cursor.getString(cursor.getColumnIndex("colmn2")));
} while (cursor.moveToNext());
}
cursor.close();
return map;
} catch (Exception e) {
e.printStackTrace();
Log.e("getdata", "Ended");
}
return null;
}
In this demo only the response coming as I explained above.And then am doing this 在这个演示中,只有我上面解释的响应。然后我正在做这个
if(demo.isEmpty())
{
//code for correct condition
}
else
{
demo.clear();
}
And passing the values to hash map by this way. 并通过这种方式将值传递给哈希映射。
demo = dbhelper.getdata();
And My Logcat exceptions: 和我的Logcat例外:
09-06 12:48:53.656: W/dalvikvm(5071): threadid=1: thread exiting with uncaught exception (group=0x40fb0258)
09-06 12:48:53.660: W/System.err(5071): java.lang.RuntimeException: Unable to start activity ComponentInfo{packagename/packagename.listdata}: java.lang.NullPointerException
09-06 12:48:53.660: W/System.err(5071): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2077)
09-06 12:48:53.660: W/System.err(5071): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2104)
09-06 12:48:53.660: W/System.err(5071): at android.app.ActivityThread.access$600(ActivityThread.java:134)
09-06 12:48:53.660: W/System.err(5071): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1247)
09-06 12:48:53.660: W/System.err(5071): at android.os.Handler.dispatchMessage(Handler.java:99)
09-06 12:48:53.660: W/System.err(5071): at android.os.Looper.loop(Looper.java:154)
09-06 12:48:53.660: W/System.err(5071): at android.app.ActivityThread.main(ActivityThread.java:4624)
09-06 12:48:53.661: W/System.err(5071): at java.lang.reflect.Method.invokeNative(Native Method)
09-06 12:48:53.661: W/System.err(5071): at java.lang.reflect.Method.invoke(Method.java:511)
09-06 12:48:53.661: W/System.err(5071): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:809)
09-06 12:48:53.661: W/System.err(5071): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:576)
09-06 12:48:53.661: W/System.err(5071): at dalvik.system.NativeStart.main(Native Method)
09-06 12:48:53.661: W/System.err(5071): Caused by: java.lang.NullPointerException
09-06 12:48:53.661: W/System.err(5071): at packagename.listdata.onCreate(listdata.java:231)
09-06 12:48:53.661: W/System.err(5071): at android.app.Activity.performCreate(Activity.java:4479)
09-06 12:48:53.661: W/System.err(5071): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1050)
09-06 12:48:53.661: W/System.err(5071): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2041)
hMap.clear()
always worked fine for me. hMap.clear()
总是对我很好。
Still 仍然
hMap.put("A","test");
will automatically override the existing value for key "A". 将自动覆盖键“A”的现有值。
If you still wish to clear values, 如果您仍希望清除值,
You can use 您可以使用
hMap = new HashMap<String,String>();
which will initialize a new hashmap in hMap
. 这将在hMap
初始化一个新的hashmap。
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