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POAndroid update SQLite with GSON response ... how should I parse nested JSON?
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  1. POAndroid update SQLite with GSON response ... how should I parse nested JSON?
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    copied!<p>I have tried to figure this out on my own... starting with two excellent tutorials on GSON parsing from <a href="http://blog.brianbuikema.com/2010/04/android-how-to-deserialize-both-xml-and-json/" rel="nofollow">High-Speed Blog</a> and <a href="http://www.javacodegeeks.com/2011/01/android-json-parsing-gson-tutorial.html" rel="nofollow">Java Code Geeks</a>. Several [answers] (http://stackoverflow.com/questions/3763937/gson-and-deserializing-an-array-of-objects-with-arrays-in-it/6300251#6300251) on stackoverflow are relevant, but I need more help than a screendump. I want to update my SQLite database from the following JSON response:</p> <pre><code> { "Field": "13", "Plants": [ { "PlantID": 123, "PlotID": 321, "Row": 1, "Post": 1, "Position": 1, "PlotName": "Sunnyside", "Breed": "Daisy" }, { "PlantID": 149, "PlotID": 348, "Row": 1, "Post": 20, "Position": 1, "PlotName": "Waterside", "Breed": "Iris" } ] } </code></pre> <p>my root class (jsonPlots) and 'nested' class (Plants) are as follows:</p> <pre><code> public class jsonPlots { @SerializedName("Field") public String mFieldId; public ArrayList&lt;Plants&gt; PlantArray; } public class Plants { @SerializedName("PlantID") public int jPlantID; @SerializedName("PlotID") public int jPlotID; @SerializedName("Row") public int jRow; @SerializedName("Post") public int jPost; @SerializedName("Position") public int jPosition; @SerializedName("PlotName") public String jPlotName; @SerializedName("Breed") public String jBreed; } </code></pre> <p>I have verified that I am getting a valid response using the following snippet:</p> <pre><code> public void getJsonData() { InputStream source = retrieveStream(url); Gson gson = new Gson(); Reader reader = new InputStreamReader(source); jsonPlots response = gson.fromJson(reader, jsonPlots.class); Toast.makeText(this, response.mFieldId, Toast.LENGTH_SHORT).show(); // this works ArrayList&lt;Plants&gt; results = response.PlantArray; if(results.isEmpty()) { /// null pointer exception here Toast.makeText(this, "no data to update", Toast.LENGTH_SHORT).show(); } else { for (Plants result : results) { try { Toast.makeText(this, result.jBreed, Toast.LENGTH_SHORT).show(); // replace with SQLite update Toast.makeText(this, result.jPlotName, Toast.LENGTH_SHORT).show(); } finally { Toast.makeText(this, "failed", Toast.LENGTH_SHORT).show(); } } } } // getJsonData </code></pre> <p>The first Toast (mFieldID) works. It crashes at <strong>if(results.isEmpty())</strong> with a null pointer exception as noted. Is my ArrayList not populating ? I would like a code suggestion on how to sequence through this nested array... so that I can systematically update my SQLite database.</p>
 

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